Input: tsc2007 - read "ti,poll-period" as u32grafted

The "ti,poll-period" property is documented as a normal uint32 cell.
The driver used a u64 helper, which makes the helper type disagree with
the schema even though the stored value is still small.

Read "ti,poll-period" with the u32 helper matching the documented DT
cell size.

Assisted-by: Codex:gpt-5-5
Signed-off-by: Rob Herring (Arm) <robh@kernel.org>
Link: https://patch.msgid.link/20260831194352.1185860-1-robh@kernel.org
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

1 files changed, 7612 insertions, 0 deletions

diff --git a/rust/zerocopy/src/lib.rs b/rust/zerocopy/src/lib.rs
new file mode 100644
index 000000000..3302d6760
--- /dev/null
+++ b/rust/zerocopy/src/lib.rs
@@ -0,0 +1,7612 @@
+// SPDX-License-Identifier: (BSD-2-Clause OR Apache-2.0) OR MIT
+
+// Copyright 2018 The Fuchsia Authors
+//
+// Licensed under the 2-Clause BSD License <LICENSE-BSD or
+// https://opensource.org/license/bsd-2-clause>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+// After updating the following doc comment, make sure to run the following
+// command to update `README.md` based on its contents:
+//
+//   cargo -q run --manifest-path tools/Cargo.toml -p generate-readme > README.md
+
+//! ***<span style="font-size: 140%">Fast, safe, <span
+//! style="color:red;">compile error</span>. Pick two.</span>***
+//!
+//! Zerocopy makes zero-cost memory manipulation effortless. We write `unsafe`
+//! so you don't have to.
+//!
+//! *For an overview of what's changed from zerocopy 0.7, check out our [release
+//! notes][release-notes], which include a step-by-step upgrading guide.*
+//!
+//! *Have questions? Need more out of zerocopy? Submit a [customer request
+//! issue][customer-request-issue] or ask the maintainers on
+//! [GitHub][github-q-a] or [Discord][discord]!*
+//!
+//! [customer-request-issue]: https://github.com/google/zerocopy/issues/new/choose
+//! [release-notes]: https://github.com/google/zerocopy/discussions/1680
+//! [github-q-a]: https://github.com/google/zerocopy/discussions/categories/q-a
+//! [discord]: https://discord.gg/MAvWH2R6zk
+//!
+//! # Overview
+//!
+//! ##### Conversion Traits
+//!
+//! Zerocopy provides four derivable traits for zero-cost conversions:
+//! - [`TryFromBytes`] indicates that a type may safely be converted from
+//!   certain byte sequences (conditional on runtime checks)
+//! - [`FromZeros`] indicates that a sequence of zero bytes represents a valid
+//!   instance of a type
+//! - [`FromBytes`] indicates that a type may safely be converted from an
+//!   arbitrary byte sequence
+//! - [`IntoBytes`] indicates that a type may safely be converted *to* a byte
+//!   sequence
+//!
+//! These traits support sized types, slices, and [slice DSTs][slice-dsts].
+//!
+//! [slice-dsts]: KnownLayout#dynamically-sized-types
+//!
+//! ##### Marker Traits
+//!
+//! Zerocopy provides three derivable marker traits that do not provide any
+//! functionality themselves, but are required to call certain methods provided
+//! by the conversion traits:
+//! - [`KnownLayout`] indicates that zerocopy can reason about certain layout
+//!   qualities of a type
+//! - [`Immutable`] indicates that a type is free from interior mutability,
+//!   except by ownership or an exclusive (`&mut`) borrow
+//! - [`Unaligned`] indicates that a type's alignment requirement is 1
+//!
+//! You should generally derive these marker traits whenever possible.
+//!
+//! ##### Conversion Macros
+//!
+//! Zerocopy provides six macros for safe casting between types:
+//!
+//! - ([`try_`][try_transmute])[`transmute`] (conditionally) converts a value of
+//!   one type to a value of another type of the same size
+//! - ([`try_`][try_transmute_mut])[`transmute_mut`] (conditionally) converts a
+//!   mutable reference of one type to a mutable reference of another type of
+//!   the same size
+//! - ([`try_`][try_transmute_ref])[`transmute_ref`] (conditionally) converts a
+//!   mutable or immutable reference of one type to an immutable reference of
+//!   another type of the same size
+//!
+//! These macros perform *compile-time* size and alignment checks, meaning that
+//! unconditional casts have zero cost at runtime. Conditional casts do not need
+//! to validate size or alignment runtime, but do need to validate contents.
+//!
+//! These macros cannot be used in generic contexts. For generic conversions,
+//! use the methods defined by the [conversion traits](#conversion-traits).
+//!
+//! ##### Byteorder-Aware Numerics
+//!
+//! Zerocopy provides byte-order aware integer types that support these
+//! conversions; see the [`byteorder`] module. These types are especially useful
+//! for network parsing.
+//!
+//! # Cargo Features
+//!
+//! - **`alloc`**
+//!   By default, `zerocopy` is `no_std`. When the `alloc` feature is enabled,
+//!   the `alloc` crate is added as a dependency, and some allocation-related
+//!   functionality is added.
+//!
+//! - **`std`**
+//!   By default, `zerocopy` is `no_std`. When the `std` feature is enabled, the
+//!   `std` crate is added as a dependency (ie, `no_std` is disabled), and
+//!   support for some `std` types is added. `std` implies `alloc`.
+//!
+//! - **`derive`**
+//!   Provides derives for the core marker traits via the `zerocopy-derive`
+//!   crate. These derives are re-exported from `zerocopy`, so it is not
+//!   necessary to depend on `zerocopy-derive` directly.
+//!
+//!   However, you may experience better compile times if you instead directly
+//!   depend on both `zerocopy` and `zerocopy-derive` in your `Cargo.toml`,
+//!   since doing so will allow Rust to compile these crates in parallel. To do
+//!   so, do *not* enable the `derive` feature, and list both dependencies in
+//!   your `Cargo.toml` with the same leading non-zero version number; e.g:
+//!
+//!   ```toml
+//!   [dependencies]
+//!   zerocopy = "0.X"
+//!   zerocopy-derive = "0.X"
+//!   ```
+//!
+//!   To avoid the risk of [duplicate import errors][duplicate-import-errors] if
+//!   one of your dependencies enables zerocopy's `derive` feature, import
+//!   derives as `use zerocopy_derive::*` rather than by name (e.g., `use
+//!   zerocopy_derive::FromBytes`).
+//!
+//! - **`simd`**
+//!   When the `simd` feature is enabled, `FromZeros`, `FromBytes`, and
+//!   `IntoBytes` impls are emitted for all stable SIMD types which exist on the
+//!   target platform. Note that the layout of SIMD types is not yet stabilized,
+//!   so these impls may be removed in the future if layout changes make them
+//!   invalid. For more information, see the Unsafe Code Guidelines Reference
+//!   page on the [layout of packed SIMD vectors][simd-layout].
+//!
+//! - **`simd-nightly`**
+//!   Enables the `simd` feature and adds support for SIMD types which are only
+//!   available on nightly. Since these types are unstable, support for any type
+//!   may be removed at any point in the future.
+//!
+//! - **`float-nightly`**
+//!   Adds support for the unstable `f16` and `f128` types. These types are
+//!   not yet fully implemented and may not be supported on all platforms.
+//!
+//! [duplicate-import-errors]: https://github.com/google/zerocopy/issues/1587
+//! [simd-layout]: https://rust-lang.github.io/unsafe-code-guidelines/layout/packed-simd-vectors.html
+//!
+//! # Build Tuning
+//!
+//! ## `--cfg zerocopy_inline_always`
+//!
+//! Upgrades `#[inline]` to `#[inline(always)]` on many of zerocopy's public
+//! functions and methods. This provides a narrowly-scoped alternative that
+//! *may* improve the optimization of hot paths using zerocopy without the broad
+//! compile-time penalties of configuring `codegen-units=1`.
+//!
+//! # Security Ethos
+//!
+//! Zerocopy is expressly designed for use in security-critical contexts. We
+//! strive to ensure that that zerocopy code is sound under Rust's current
+//! memory model, and *any future memory model*. We ensure this by:
+//! - **...not 'guessing' about Rust's semantics.**
+//!   We annotate `unsafe` code with a precise rationale for its soundness that
+//!   cites a relevant section of Rust's official documentation. When Rust's
+//!   documented semantics are unclear, we work with the Rust Operational
+//!   Semantics Team to clarify Rust's documentation.
+//! - **...rigorously testing our implementation.**
+//!   We run tests using [Miri], ensuring that zerocopy is sound across a wide
+//!   array of supported target platforms of varying endianness and pointer
+//!   width, and across both current and experimental memory models of Rust.
+//! - **...formally proving the correctness of our implementation.**
+//!   We apply formal verification tools like [Kani][kani] to prove zerocopy's
+//!   correctness.
+//!
+//! For more information, see our full [soundness policy].
+//!
+//! [Miri]: https://github.com/rust-lang/miri
+//! [Kani]: https://github.com/model-checking/kani
+//! [soundness policy]: https://github.com/google/zerocopy/blob/main/POLICIES.md#soundness
+//!
+//! # Relationship to Project Safe Transmute
+//!
+//! [Project Safe Transmute] is an official initiative of the Rust Project to
+//! develop language-level support for safer transmutation. The Project consults
+//! with crates like zerocopy to identify aspects of safer transmutation that
+//! would benefit from compiler support, and has developed an [experimental,
+//! compiler-supported analysis][mcp-transmutability] which determines whether,
+//! for a given type, any value of that type may be soundly transmuted into
+//! another type. Once this functionality is sufficiently mature, zerocopy
+//! intends to replace its internal transmutability analysis (implemented by our
+//! custom derives) with the compiler-supported one. This change will likely be
+//! an implementation detail that is invisible to zerocopy's users.
+//!
+//! Project Safe Transmute will not replace the need for most of zerocopy's
+//! higher-level abstractions. The experimental compiler analysis is a tool for
+//! checking the soundness of `unsafe` code, not a tool to avoid writing
+//! `unsafe` code altogether. For the foreseeable future, crates like zerocopy
+//! will still be required in order to provide higher-level abstractions on top
+//! of the building block provided by Project Safe Transmute.
+//!
+//! [Project Safe Transmute]: https://rust-lang.github.io/rfcs/2835-project-safe-transmute.html
+//! [mcp-transmutability]: https://github.com/rust-lang/compiler-team/issues/411
+//!
+//! # MSRV
+//!
+//! See our [MSRV policy].
+//!
+//! [MSRV policy]: https://github.com/google/zerocopy/blob/main/POLICIES.md#msrv
+//!
+//! # Changelog
+//!
+//! Zerocopy uses [GitHub Releases].
+//!
+//! [GitHub Releases]: https://github.com/google/zerocopy/releases
+//!
+//! # Thanks
+//!
+//! Zerocopy is maintained by engineers at Google with help from [many wonderful
+//! contributors][contributors]. Thank you to everyone who has lent a hand in
+//! making Rust a little more secure!
+//!
+//! [contributors]: https://github.com/google/zerocopy/graphs/contributors
+
+// Sometimes we want to use lints which were added after our MSRV.
+// `unknown_lints` is `warn` by default and we deny warnings in CI, so without
+// this attribute, any unknown lint would cause a CI failure when testing with
+// our MSRV.
+#![allow(unknown_lints, non_local_definitions, unreachable_patterns)]
+#![deny(renamed_and_removed_lints)]
+#![deny(
+    anonymous_parameters,
+    deprecated_in_future,
+    late_bound_lifetime_arguments,
+    missing_copy_implementations,
+    missing_debug_implementations,
+    missing_docs,
+    path_statements,
+    patterns_in_fns_without_body,
+    rust_2018_idioms,
+    trivial_numeric_casts,
+    unreachable_pub,
+    unsafe_op_in_unsafe_fn,
+    unused_extern_crates,
+    // We intentionally choose not to deny `unused_qualifications`. When items
+    // are added to the prelude (e.g., `core::mem::size_of`), this has the
+    // consequence of making some uses trigger this lint on the latest toolchain
+    // (e.g., `mem::size_of`), but fixing it (e.g. by replacing with `size_of`)
+    // does not work on older toolchains.
+    //
+    // We tested a more complicated fix in #1413, but ultimately decided that,
+    // since this lint is just a minor style lint, the complexity isn't worth it
+    // - it's fine to occasionally have unused qualifications slip through,
+    // especially since these do not affect our user-facing API in any way.
+    variant_size_differences
+)]
+#![cfg_attr(
+    __ZEROCOPY_INTERNAL_USE_ONLY_NIGHTLY_FEATURES_IN_TESTS,
+    deny(fuzzy_provenance_casts, lossy_provenance_casts)
+)]
+#![deny(
+    clippy::all,
+    clippy::alloc_instead_of_core,
+    clippy::arithmetic_side_effects,
+    clippy::as_underscore,
+    clippy::assertions_on_result_states,
+    clippy::as_conversions,
+    clippy::correctness,
+    clippy::dbg_macro,
+    clippy::decimal_literal_representation,
+    clippy::double_must_use,
+    clippy::get_unwrap,
+    clippy::indexing_slicing,
+    clippy::missing_inline_in_public_items,
+    clippy::missing_safety_doc,
+    clippy::multiple_unsafe_ops_per_block,
+    clippy::must_use_candidate,
+    clippy::must_use_unit,
+    clippy::obfuscated_if_else,
+    clippy::perf,
+    clippy::print_stdout,
+    clippy::return_self_not_must_use,
+    clippy::std_instead_of_core,
+    clippy::style,
+    clippy::suspicious,
+    clippy::todo,
+    clippy::undocumented_unsafe_blocks,
+    clippy::unimplemented,
+    clippy::unnested_or_patterns,
+    clippy::unwrap_used,
+    clippy::use_debug
+)]
+// `clippy::incompatible_msrv` (implied by `clippy::suspicious`): This sometimes
+// has false positives, and we test on our MSRV in CI, so it doesn't help us
+// anyway.
+#![allow(clippy::needless_lifetimes, clippy::type_complexity, clippy::incompatible_msrv)]
+#![deny(
+    rustdoc::bare_urls,
+    rustdoc::broken_intra_doc_links,
+    rustdoc::invalid_codeblock_attributes,
+    rustdoc::invalid_html_tags,
+    rustdoc::invalid_rust_codeblocks,
+    rustdoc::missing_crate_level_docs,
+    rustdoc::private_intra_doc_links
+)]
+// In test code, it makes sense to weight more heavily towards concise, readable
+// code over correct or debuggable code.
+#![cfg_attr(any(test, kani), allow(
+    // In tests, you get line numbers and have access to source code, so panic
+    // messages are less important. You also often unwrap a lot, which would
+    // make expect'ing instead very verbose.
+    clippy::unwrap_used,
+    // In tests, there's no harm to "panic risks" - the worst that can happen is
+    // that your test will fail, and you'll fix it. By contrast, panic risks in
+    // production code introduce the possibly of code panicking unexpectedly "in
+    // the field".
+    clippy::arithmetic_side_effects,
+    clippy::indexing_slicing,
+))]
+#![cfg_attr(not(any(test, kani, feature = "std")), no_std)]
+#![cfg_attr(
+    all(feature = "simd-nightly", target_arch = "arm"),
+    feature(stdarch_arm_neon_intrinsics)
+)]
+#![cfg_attr(
+    all(feature = "simd-nightly", any(target_arch = "powerpc", target_arch = "powerpc64")),
+    feature(stdarch_powerpc)
+)]
+#![cfg_attr(feature = "float-nightly", feature(f16, f128))]
+#![cfg_attr(doc_cfg, feature(doc_cfg))]
+#![cfg_attr(__ZEROCOPY_INTERNAL_USE_ONLY_NIGHTLY_FEATURES_IN_TESTS, feature(coverage_attribute))]
+#![cfg_attr(
+    any(__ZEROCOPY_INTERNAL_USE_ONLY_NIGHTLY_FEATURES_IN_TESTS, miri),
+    feature(layout_for_ptr)
+)]
+#![cfg_attr(all(test, __ZEROCOPY_INTERNAL_USE_ONLY_NIGHTLY_FEATURES_IN_TESTS), feature(test))]
+
+// This is a hack to allow zerocopy-derive derives to work in this crate. They
+// assume that zerocopy is linked as an extern crate, so they access items from
+// it as `zerocopy::Xxx`. This makes that still work.
+#[cfg(any(feature = "derive", test))]
+extern crate self as zerocopy;
+
+#[cfg(all(test, __ZEROCOPY_INTERNAL_USE_ONLY_NIGHTLY_FEATURES_IN_TESTS))]
+extern crate test;
+
+#[doc(hidden)]
+#[macro_use]
+pub mod util;
+
+pub mod byte_slice;
+pub mod byteorder;
+mod deprecated;
+
+#[cfg(__ZEROCOPY_INTERNAL_USE_ONLY_DEV_MODE)]
+pub mod doctests;
+
+// This module is `pub` so that zerocopy's error types and error handling
+// documentation is grouped together in a cohesive module. In practice, we
+// expect most users to use the re-export of `error`'s items to avoid identifier
+// stuttering.
+pub mod error;
+mod impls;
+#[doc(hidden)]
+pub mod layout;
+mod macros;
+#[cfg_attr(not(zerocopy_unstable_ptr), doc(hidden))]
+#[cfg_attr(doc_cfg, doc(cfg(zerocopy_unstable_ptr)))]
+pub mod pointer;
+mod r#ref;
+mod split_at;
+// FIXME(#252): If we make this pub, come up with a better name.
+mod wrappers;
+
+use core::{
+    cell::{Cell, UnsafeCell},
+    cmp::Ordering,
+    fmt::{self, Debug, Display, Formatter},
+    hash::Hasher,
+    marker::PhantomData,
+    mem::{self, ManuallyDrop, MaybeUninit as CoreMaybeUninit},
+    num::{
+        NonZeroI128, NonZeroI16, NonZeroI32, NonZeroI64, NonZeroI8, NonZeroIsize, NonZeroU128,
+        NonZeroU16, NonZeroU32, NonZeroU64, NonZeroU8, NonZeroUsize, Wrapping,
+    },
+    ops::{Deref, DerefMut},
+    ptr::{self, NonNull},
+    slice,
+};
+#[cfg(feature = "std")]
+use std::io;
+
+#[doc(hidden)]
+pub use crate::pointer::{
+    invariant::{self, BecauseExclusive},
+    PtrInner,
+};
+pub use crate::{
+    byte_slice::*,
+    byteorder::*,
+    error::*,
+    r#ref::*,
+    split_at::{Split, SplitAt},
+    wrappers::*,
+};
+
+#[cfg(any(feature = "alloc", test, kani))]
+extern crate alloc;
+#[cfg(any(feature = "alloc", test))]
+use alloc::{boxed::Box, vec::Vec};
+#[cfg(any(feature = "alloc", test))]
+use core::alloc::Layout;
+
+// Used by `KnownLayout`.
+#[doc(hidden)]
+pub use crate::layout::*;
+// Used by `TryFromBytes::is_bit_valid`.
+#[doc(hidden)]
+pub use crate::pointer::{invariant::BecauseImmutable, Maybe, Ptr};
+// For each trait polyfill, as soon as the corresponding feature is stable, the
+// polyfill import will be unused because method/function resolution will prefer
+// the inherent method/function over a trait method/function. Thus, we suppress
+// the `unused_imports` warning.
+//
+// See the documentation on `util::polyfills` for more information.
+#[allow(unused_imports)]
+use crate::util::polyfills::{self, NonNullExt as _, NumExt as _};
+#[cfg_attr(not(zerocopy_unstable_ptr), doc(hidden))]
+#[cfg_attr(doc_cfg, doc(cfg(zerocopy_unstable_ptr)))]
+pub use crate::util::MetadataOf;
+
+#[cfg(all(test, not(__ZEROCOPY_INTERNAL_USE_ONLY_DEV_MODE)))]
+const _: () = {
+    #[deprecated = "Development of zerocopy using cargo is not supported. Please use `cargo.sh` or `win-cargo.bat` instead."]
+    #[allow(unused)]
+    const WARNING: () = ();
+    #[warn(deprecated)]
+    WARNING
+};
+
+/// Implements [`KnownLayout`].
+///
+/// This derive analyzes various aspects of a type's layout that are needed for
+/// some of zerocopy's APIs. It can be applied to structs, enums, and unions;
+/// e.g.:
+///
+/// ```
+/// # use zerocopy_derive::KnownLayout;
+/// #[derive(KnownLayout)]
+/// struct MyStruct {
+/// # /*
+///     ...
+/// # */
+/// }
+///
+/// #[derive(KnownLayout)]
+/// enum MyEnum {
+/// #   V00,
+/// # /*
+///     ...
+/// # */
+/// }
+///
+/// #[derive(KnownLayout)]
+/// union MyUnion {
+/// #   variant: u8,
+/// # /*
+///     ...
+/// # */
+/// }
+/// ```
+///
+/// # Limitations
+///
+/// This derive cannot currently be applied to unsized structs without an
+/// explicit `repr` attribute.
+///
+/// Some invocations of this derive run afoul of a [known bug] in Rust's type
+/// privacy checker. For example, this code:
+///
+/// ```compile_fail,E0446
+/// use zerocopy::*;
+/// # use zerocopy_derive::*;
+///
+/// #[derive(KnownLayout)]
+/// #[repr(C)]
+/// pub struct PublicType {
+///     leading: Foo,
+///     trailing: Bar,
+/// }
+///
+/// #[derive(KnownLayout)]
+/// struct Foo;
+///
+/// #[derive(KnownLayout)]
+/// struct Bar;
+/// ```
+///
+/// ...results in a compilation error:
+///
+/// ```text
+/// error[E0446]: private type `Bar` in public interface
+///  --> examples/bug.rs:3:10
+///    |
+/// 3  | #[derive(KnownLayout)]
+///    |          ^^^^^^^^^^^ can't leak private type
+/// ...
+/// 14 | struct Bar;
+///    | ---------- `Bar` declared as private
+///    |
+///    = note: this error originates in the derive macro `KnownLayout` (in Nightly builds, run with -Z macro-backtrace for more info)
+/// ```
+///
+/// This issue arises when `#[derive(KnownLayout)]` is applied to `repr(C)`
+/// structs whose trailing field type is less public than the enclosing struct.
+///
+/// To work around this, mark the trailing field type `pub` and annotate it with
+/// `#[doc(hidden)]`; e.g.:
+///
+/// ```no_run
+/// use zerocopy::*;
+/// # use zerocopy_derive::*;
+///
+/// #[derive(KnownLayout)]
+/// #[repr(C)]
+/// pub struct PublicType {
+///     leading: Foo,
+///     trailing: Bar,
+/// }
+///
+/// #[derive(KnownLayout)]
+/// struct Foo;
+///
+/// #[doc(hidden)]
+/// #[derive(KnownLayout)]
+/// pub struct Bar; // <- `Bar` is now also `pub`
+/// ```
+///
+/// [known bug]: https://github.com/rust-lang/rust/issues/45713
+#[cfg(any(feature = "derive", test))]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "derive")))]
+pub use zerocopy_derive::KnownLayout;
+// These exist so that code which was written against the old names will get
+// less confusing error messages when they upgrade to a more recent version of
+// zerocopy. On our MSRV toolchain, the error messages read, for example:
+//
+//   error[E0603]: trait `FromZeroes` is private
+//       --> examples/deprecated.rs:1:15
+//        |
+//   1    | use zerocopy::FromZeroes;
+//        |               ^^^^^^^^^^ private trait
+//        |
+//   note: the trait `FromZeroes` is defined here
+//       --> /Users/josh/workspace/zerocopy/src/lib.rs:1845:5
+//        |
+//   1845 | use FromZeros as FromZeroes;
+//        |     ^^^^^^^^^^^^^^^^^^^^^^^
+//
+// The "note" provides enough context to make it easy to figure out how to fix
+// the error.
+#[allow(unused)]
+use {FromZeros as FromZeroes, IntoBytes as AsBytes, Ref as LayoutVerified};
+
+/// Indicates that zerocopy can reason about certain aspects of a type's layout.
+///
+/// This trait is required by many of zerocopy's APIs. It supports sized types,
+/// slices, and [slice DSTs](#dynamically-sized-types).
+///
+/// # Implementation
+///
+/// **Do not implement this trait yourself!** Instead, use
+/// [`#[derive(KnownLayout)]`][derive]; e.g.:
+///
+/// ```
+/// # use zerocopy_derive::KnownLayout;
+/// #[derive(KnownLayout)]
+/// struct MyStruct {
+/// # /*
+///     ...
+/// # */
+/// }
+///
+/// #[derive(KnownLayout)]
+/// enum MyEnum {
+/// # /*
+///     ...
+/// # */
+/// }
+///
+/// #[derive(KnownLayout)]
+/// union MyUnion {
+/// #   variant: u8,
+/// # /*
+///     ...
+/// # */
+/// }
+/// ```
+///
+/// This derive performs a sophisticated analysis to deduce the layout
+/// characteristics of types. You **must** implement this trait via the derive.
+///
+/// # Dynamically-sized types
+///
+/// `KnownLayout` supports slice-based dynamically sized types ("slice DSTs").
+///
+/// A slice DST is a type whose trailing field is either a slice or another
+/// slice DST, rather than a type with fixed size. For example:
+///
+/// ```
+/// #[repr(C)]
+/// struct PacketHeader {
+/// # /*
+///     ...
+/// # */
+/// }
+///
+/// #[repr(C)]
+/// struct Packet {
+///     header: PacketHeader,
+///     body: [u8],
+/// }
+/// ```
+///
+/// It can be useful to think of slice DSTs as a generalization of slices - in
+/// other words, a normal slice is just the special case of a slice DST with
+/// zero leading fields. In particular:
+/// - Like slices, slice DSTs can have different lengths at runtime
+/// - Like slices, slice DSTs cannot be passed by-value, but only by reference
+///   or via other indirection such as `Box`
+/// - Like slices, a reference (or `Box`, or other pointer type) to a slice DST
+///   encodes the number of elements in the trailing slice field
+///
+/// ## Slice DST layout
+///
+/// Just like other composite Rust types, the layout of a slice DST is not
+/// well-defined unless it is specified using an explicit `#[repr(...)]`
+/// attribute such as `#[repr(C)]`. [Other representations are
+/// supported][reprs], but in this section, we'll use `#[repr(C)]` as our
+/// example.
+///
+/// A `#[repr(C)]` slice DST is laid out [just like sized `#[repr(C)]`
+/// types][repr-c-structs], but the presence of a variable-length field
+/// introduces the possibility of *dynamic padding*. In particular, it may be
+/// necessary to add trailing padding *after* the trailing slice field in order
+/// to satisfy the outer type's alignment, and the amount of padding required
+/// may be a function of the length of the trailing slice field. This is just a
+/// natural consequence of the normal `#[repr(C)]` rules applied to slice DSTs,
+/// but it can result in surprising behavior. For example, consider the
+/// following type:
+///
+/// ```
+/// #[repr(C)]
+/// struct Foo {
+///     a: u32,
+///     b: u8,
+///     z: [u16],
+/// }
+/// ```
+///
+/// Assuming that `u32` has alignment 4 (this is not true on all platforms),
+/// then `Foo` has alignment 4 as well. Here is the smallest possible value for
+/// `Foo`:
+///
+/// ```text
+/// byte offset | 01234567
+///       field | aaaab---
+///                    ><
+/// ```
+///
+/// In this value, `z` has length 0. Abiding by `#[repr(C)]`, the lowest offset
+/// that we can place `z` at is 5, but since `z` has alignment 2, we need to
+/// round up to offset 6. This means that there is one byte of padding between
+/// `b` and `z`, then 0 bytes of `z` itself (denoted `><` in this diagram), and
+/// then two bytes of padding after `z` in order to satisfy the overall
+/// alignment of `Foo`. The size of this instance is 8 bytes.
+///
+/// What about if `z` has length 1?
+///
+/// ```text
+/// byte offset | 01234567
+///       field | aaaab-zz
+/// ```
+///
+/// In this instance, `z` has length 1, and thus takes up 2 bytes. That means
+/// that we no longer need padding after `z` in order to satisfy `Foo`'s
+/// alignment. We've now seen two different values of `Foo` with two different
+/// lengths of `z`, but they both have the same size - 8 bytes.
+///
+/// What about if `z` has length 2?
+///
+/// ```text
+/// byte offset | 012345678901
+///       field | aaaab-zzzz--
+/// ```
+///
+/// Now `z` has length 2, and thus takes up 4 bytes. This brings our un-padded
+/// size to 10, and so we now need another 2 bytes of padding after `z` to
+/// satisfy `Foo`'s alignment.
+///
+/// Again, all of this is just a logical consequence of the `#[repr(C)]` rules
+/// applied to slice DSTs, but it can be surprising that the amount of trailing
+/// padding becomes a function of the trailing slice field's length, and thus
+/// can only be computed at runtime.
+///
+/// [reprs]: https://doc.rust-lang.org/reference/type-layout.html#representations
+/// [repr-c-structs]: https://doc.rust-lang.org/reference/type-layout.html#reprc-structs
+///
+/// ## What is a valid size?
+///
+/// There are two places in zerocopy's API that we refer to "a valid size" of a
+/// type. In normal casts or conversions, where the source is a byte slice, we
+/// need to know whether the source byte slice is a valid size of the
+/// destination type. In prefix or suffix casts, we need to know whether *there
+/// exists* a valid size of the destination type which fits in the source byte
+/// slice and, if so, what the largest such size is.
+///
+/// As outlined above, a slice DST's size is defined by the number of elements
+/// in its trailing slice field. However, there is not necessarily a 1-to-1
+/// mapping between trailing slice field length and overall size. As we saw in
+/// the previous section with the type `Foo`, instances with both 0 and 1
+/// elements in the trailing `z` field result in a `Foo` whose size is 8 bytes.
+///
+/// When we say "x is a valid size of `T`", we mean one of two things:
+/// - If `T: Sized`, then we mean that `x == size_of::<T>()`
+/// - If `T` is a slice DST, then we mean that there exists a `len` such that the instance of
+///   `T` with `len` trailing slice elements has size `x`
+///
+/// When we say "largest possible size of `T` that fits in a byte slice", we
+/// mean one of two things:
+/// - If `T: Sized`, then we mean `size_of::<T>()` if the byte slice is at least
+///   `size_of::<T>()` bytes long
+/// - If `T` is a slice DST, then we mean to consider all values, `len`, such
+///   that the instance of `T` with `len` trailing slice elements fits in the
+///   byte slice, and to choose the largest such `len`, if any
+///
+///
+/// # Safety
+///
+/// This trait does not convey any safety guarantees to code outside this crate.
+///
+/// You must not rely on the `#[doc(hidden)]` internals of `KnownLayout`. Future
+/// releases of zerocopy may make backwards-breaking changes to these items,
+/// including changes that only affect soundness, which may cause code which
+/// uses those items to silently become unsound.
+///
+#[cfg_attr(feature = "derive", doc = "[derive]: zerocopy_derive::KnownLayout")]
+#[cfg_attr(
+    not(feature = "derive"),
+    doc = concat!("[derive]: https://docs.rs/zerocopy/", env!("CARGO_PKG_VERSION"), "/zerocopy/derive.KnownLayout.html"),
+)]
+#[cfg_attr(
+    not(no_zerocopy_diagnostic_on_unimplemented_1_78_0),
+    diagnostic::on_unimplemented(note = "Consider adding `#[derive(KnownLayout)]` to `{Self}`")
+)]
+pub unsafe trait KnownLayout {
+    // The `Self: Sized` bound makes it so that `KnownLayout` can still be
+    // object safe. It's not currently object safe thanks to `const LAYOUT`, and
+    // it likely won't be in the future, but there's no reason not to be
+    // forwards-compatible with object safety.
+    #[doc(hidden)]
+    fn only_derive_is_allowed_to_implement_this_trait()
+    where
+        Self: Sized;
+
+    /// The type of metadata stored in a pointer to `Self`.
+    ///
+    /// This is `()` for sized types and [`usize`] for slice DSTs.
+    type PointerMetadata: PointerMetadata;
+
+    /// A maybe-uninitialized analog of `Self`
+    ///
+    /// # Safety
+    ///
+    /// `Self::LAYOUT` and `Self::MaybeUninit::LAYOUT` are identical.
+    /// `Self::MaybeUninit` admits uninitialized bytes in all positions.
+    #[doc(hidden)]
+    type MaybeUninit: ?Sized + KnownLayout<PointerMetadata = Self::PointerMetadata>;
+
+    /// The layout of `Self`.
+    ///
+    /// # Safety
+    ///
+    /// Callers may assume that `LAYOUT` accurately reflects the layout of
+    /// `Self`. In particular:
+    /// - `LAYOUT.align` is equal to `Self`'s alignment
+    /// - If `Self: Sized`, then `LAYOUT.size_info == SizeInfo::Sized { size }`
+    ///   where `size == size_of::<Self>()`
+    /// - If `Self` is a slice DST, then `LAYOUT.size_info ==
+    ///   SizeInfo::SliceDst(slice_layout)` where:
+    ///   - The size, `size`, of an instance of `Self` with `elems` trailing
+    ///     slice elements is equal to `slice_layout.offset +
+    ///     slice_layout.elem_size * elems` rounded up to the nearest multiple
+    ///     of `LAYOUT.align`
+    ///   - For such an instance, any bytes in the range `[slice_layout.offset +
+    ///     slice_layout.elem_size * elems, size)` are padding and must not be
+    ///     assumed to be initialized
+    #[doc(hidden)]
+    const LAYOUT: DstLayout;
+
+    /// SAFETY: The returned pointer has the same address and provenance as
+    /// `bytes`. If `Self` is a DST, the returned pointer's referent has `elems`
+    /// elements in its trailing slice.
+    #[doc(hidden)]
+    fn raw_from_ptr_len(bytes: NonNull<u8>, meta: Self::PointerMetadata) -> NonNull<Self>;
+
+    /// Extracts the metadata from a pointer to `Self`.
+    ///
+    /// # Safety
+    ///
+    /// `pointer_to_metadata` always returns the correct metadata stored in
+    /// `ptr`.
+    #[doc(hidden)]
+    fn pointer_to_metadata(ptr: *mut Self) -> Self::PointerMetadata;
+
+    /// Computes the length of the byte range addressed by `ptr`.
+    ///
+    /// Returns `None` if the resulting length would not fit in an `usize`.
+    ///
+    /// # Safety
+    ///
+    /// Callers may assume that `size_of_val_raw` always returns the correct
+    /// size.
+    ///
+    /// Callers may assume that, if `ptr` addresses a byte range whose length
+    /// fits in an `usize`, this will return `Some`.
+    #[doc(hidden)]
+    #[must_use]
+    #[inline(always)]
+    fn size_of_val_raw(ptr: NonNull<Self>) -> Option<usize> {
+        let meta = Self::pointer_to_metadata(ptr.as_ptr());
+        // SAFETY: `size_for_metadata` promises to only return `None` if the
+        // resulting size would not fit in a `usize`.
+        Self::size_for_metadata(meta)
+    }
+
+    #[doc(hidden)]
+    #[must_use]
+    #[inline(always)]
+    fn raw_dangling() -> NonNull<Self> {
+        let meta = Self::PointerMetadata::from_elem_count(0);
+        Self::raw_from_ptr_len(NonNull::dangling(), meta)
+    }
+
+    /// Computes the size of an object of type `Self` with the given pointer
+    /// metadata.
+    ///
+    /// # Safety
+    ///
+    /// `size_for_metadata` promises to return `None` if and only if the
+    /// resulting size would not fit in a [`usize`]. Note that the returned size
+    /// could exceed the actual maximum valid size of an allocated object,
+    /// [`isize::MAX`].
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use zerocopy::KnownLayout;
+    ///
+    /// assert_eq!(u8::size_for_metadata(()), Some(1));
+    /// assert_eq!(u16::size_for_metadata(()), Some(2));
+    /// assert_eq!(<[u8]>::size_for_metadata(42), Some(42));
+    /// assert_eq!(<[u16]>::size_for_metadata(42), Some(84));
+    ///
+    /// // This size exceeds the maximum valid object size (`isize::MAX`):
+    /// assert_eq!(<[u8]>::size_for_metadata(usize::MAX), Some(usize::MAX));
+    ///
+    /// // This size, if computed, would exceed `usize::MAX`:
+    /// assert_eq!(<[u16]>::size_for_metadata(usize::MAX), None);
+    /// ```
+    #[inline(always)]
+    fn size_for_metadata(meta: Self::PointerMetadata) -> Option<usize> {
+        meta.size_for_metadata(Self::LAYOUT)
+    }
+
+    /// Computes whether `meta` can describe a valid allocation of `Self`.
+    ///
+    /// # Safety
+    ///
+    /// `is_valid_metadata` promises to return `true` if and only if the size of
+    /// an allocation of `Self` with `meta` would not overflow an
+    /// [`isize::MAX`].
+    #[doc(hidden)]
+    #[inline(always)]
+    fn is_valid_metadata(meta: Self::PointerMetadata) -> bool {
+        meta.to_elem_count() <= maximum_trailing_slice_len::<Self>().to_elem_count()
+    }
+}
+
+/// Efficiently produces the [`TrailingSliceLayout`] of `T`.
+#[inline(always)]
+pub(crate) fn trailing_slice_layout<T>() -> TrailingSliceLayout
+where
+    T: ?Sized + KnownLayout<PointerMetadata = usize>,
+{
+    trait LayoutFacts {
+        const SIZE_INFO: TrailingSliceLayout;
+    }
+
+    impl<T: ?Sized> LayoutFacts for T
+    where
+        T: KnownLayout<PointerMetadata = usize>,
+    {
+        const SIZE_INFO: TrailingSliceLayout = match T::LAYOUT.size_info {
+            crate::SizeInfo::Sized { .. } => const_panic!("unreachable"),
+            crate::SizeInfo::SliceDst(info) => info,
+        };
+    }
+
+    T::SIZE_INFO
+}
+
+/// Efficiently produces the maximum trailing slice length `T`.
+#[inline(always)]
+pub(crate) fn maximum_trailing_slice_len<T>() -> usize
+where
+    T: ?Sized + KnownLayout,
+{
+    trait LayoutFacts {
+        const MAX_LEN: usize;
+    }
+
+    impl<T: ?Sized> LayoutFacts for T
+    where
+        T: KnownLayout,
+    {
+        const MAX_LEN: usize = match T::LAYOUT.size_info {
+            SizeInfo::SliceDst(TrailingSliceLayout { elem_size: 0, .. }) => usize::MAX,
+            _ => match T::LAYOUT.validate_cast_and_convert_metadata(
+                T::LAYOUT.align.get(),
+                DstLayout::MAX_SIZE,
+                CastType::Prefix,
+            ) {
+                Ok((elems, _)) => elems,
+                Err(_) => const_panic!("unreachable"),
+            },
+        };
+    }
+
+    T::MAX_LEN
+}
+
+/// The metadata associated with a [`KnownLayout`] type.
+#[doc(hidden)]
+pub trait PointerMetadata: Copy + Eq + Debug + Ord {
+    /// Constructs a `Self` from an element count.
+    ///
+    /// If `Self = ()`, this returns `()`. If `Self = usize`, this returns
+    /// `elems`. No other types are currently supported.
+    fn from_elem_count(elems: usize) -> Self;
+
+    /// Converts `self` to an element count.
+    ///
+    /// If `Self = ()`, this returns `0`. If `Self = usize`, this returns
+    /// `self`. No other types are currently supported.
+    fn to_elem_count(self) -> usize;
+
+    /// Computes the size of the object with the given layout and pointer
+    /// metadata.
+    ///
+    /// # Panics
+    ///
+    /// If `Self = ()`, `layout` must describe a sized type. If `Self = usize`,
+    /// `layout` must describe a slice DST. Otherwise, `size_for_metadata` may
+    /// panic.
+    ///
+    /// # Safety
+    ///
+    /// `size_for_metadata` promises to only return `None` if the resulting size
+    /// would not fit in a `usize`.
+    fn size_for_metadata(self, layout: DstLayout) -> Option<usize>;
+}
+
+impl PointerMetadata for () {
+    #[inline]
+    #[allow(clippy::unused_unit)]
+    fn from_elem_count(_elems: usize) -> () {}
+
+    #[inline]
+    fn to_elem_count(self) -> usize {
+        0
+    }
+
+    #[inline]
+    fn size_for_metadata(self, layout: DstLayout) -> Option<usize> {
+        match layout.size_info {
+            SizeInfo::Sized { size } => Some(size),
+            // NOTE: This branch is unreachable, but we return `None` rather
+            // than `unreachable!()` to avoid generating panic paths.
+            SizeInfo::SliceDst(_) => None,
+        }
+    }
+}
+
+impl PointerMetadata for usize {
+    #[inline]
+    fn from_elem_count(elems: usize) -> usize {
+        elems
+    }
+
+    #[inline]
+    fn to_elem_count(self) -> usize {
+        self
+    }
+
+    #[inline]
+    fn size_for_metadata(self, layout: DstLayout) -> Option<usize> {
+        match layout.size_info {
+            SizeInfo::SliceDst(TrailingSliceLayout { offset, elem_size }) => {
+                let slice_len = elem_size.checked_mul(self)?;
+                let without_padding = offset.checked_add(slice_len)?;
+                without_padding.checked_add(util::padding_needed_for(without_padding, layout.align))
+            }
+            // NOTE: This branch is unreachable, but we return `None` rather
+            // than `unreachable!()` to avoid generating panic paths.
+            SizeInfo::Sized { .. } => None,
+        }
+    }
+}
+
+// SAFETY: Delegates safety to `DstLayout::for_slice`.
+unsafe impl<T> KnownLayout for [T] {
+    #[allow(clippy::missing_inline_in_public_items, dead_code)]
+    #[cfg_attr(
+        all(coverage_nightly, __ZEROCOPY_INTERNAL_USE_ONLY_NIGHTLY_FEATURES_IN_TESTS),
+        coverage(off)
+    )]
+    fn only_derive_is_allowed_to_implement_this_trait()
+    where
+        Self: Sized,
+    {
+    }
+
+    type PointerMetadata = usize;
+
+    // SAFETY: `CoreMaybeUninit<T>::LAYOUT` and `T::LAYOUT` are identical
+    // because `CoreMaybeUninit<T>` has the same size and alignment as `T` [1].
+    // Consequently, `[CoreMaybeUninit<T>]::LAYOUT` and `[T]::LAYOUT` are
+    // identical, because they both lack a fixed-sized prefix and because they
+    // inherit the alignments of their inner element type (which are identical)
+    // [2][3].
+    //
+    // `[CoreMaybeUninit<T>]` admits uninitialized bytes at all positions
+    // because `CoreMaybeUninit<T>` admits uninitialized bytes at all positions
+    // and because the inner elements of `[CoreMaybeUninit<T>]` are laid out
+    // back-to-back [2][3].
+    //
+    // [1] Per https://doc.rust-lang.org/1.81.0/std/mem/union.MaybeUninit.html#layout-1:
+    //
+    //   `MaybeUninit<T>` is guaranteed to have the same size, alignment, and ABI as
+    //   `T`
+    //
+    // [2] Per https://doc.rust-lang.org/1.82.0/reference/type-layout.html#slice-layout:
+    //
+    //   Slices have the same layout as the section of the array they slice.
+    //
+    // [3] Per https://doc.rust-lang.org/1.82.0/reference/type-layout.html#array-layout:
+    //
+    //   An array of `[T; N]` has a size of `size_of::<T>() * N` and the same
+    //   alignment of `T`. Arrays are laid out so that the zero-based `nth`
+    //   element of the array is offset from the start of the array by `n *
+    //   size_of::<T>()` bytes.
+    type MaybeUninit = [CoreMaybeUninit<T>];
+
+    const LAYOUT: DstLayout = DstLayout::for_slice::<T>();
+
+    // SAFETY: `.cast` preserves address and provenance. The returned pointer
+    // refers to an object with `elems` elements by construction.
+    #[inline(always)]
+    fn raw_from_ptr_len(data: NonNull<u8>, elems: usize) -> NonNull<Self> {
+        // FIXME(#67): Remove this allow. See NonNullExt for more details.
+        #[allow(unstable_name_collisions)]
+        NonNull::slice_from_raw_parts(data.cast::<T>(), elems)
+    }
+
+    #[inline(always)]
+    fn pointer_to_metadata(ptr: *mut [T]) -> usize {
+        #[allow(clippy::as_conversions)]
+        let slc = ptr as *const [()];
+
+        // SAFETY:
+        // - `()` has alignment 1, so `slc` is trivially aligned.
+        // - `slc` was derived from a non-null pointer.
+        // - The size is 0 regardless of the length, so it is sound to
+        //   materialize a reference regardless of location.
+        // - By invariant, `self.ptr` has valid provenance.
+        let slc = unsafe { &*slc };
+
+        // This is correct because the preceding `as` cast preserves the number
+        // of slice elements. [1]
+        //
+        // [1] Per https://doc.rust-lang.org/reference/expressions/operator-expr.html#pointer-to-pointer-cast:
+        //
+        //   For slice types like `[T]` and `[U]`, the raw pointer types `*const
+        //   [T]`, `*mut [T]`, `*const [U]`, and `*mut [U]` encode the number of
+        //   elements in this slice. Casts between these raw pointer types
+        //   preserve the number of elements. ... The same holds for `str` and
+        //   any compound type whose unsized tail is a slice type, such as
+        //   struct `Foo(i32, [u8])` or `(u64, Foo)`.
+        slc.len()
+    }
+}
+
+#[rustfmt::skip]
+impl_known_layout!(
+    (),
+    u8, i8, u16, i16, u32, i32, u64, i64, u128, i128, usize, isize, f32, f64,
+    bool, char,
+    NonZeroU8, NonZeroI8, NonZeroU16, NonZeroI16, NonZeroU32, NonZeroI32,
+    NonZeroU64, NonZeroI64, NonZeroU128, NonZeroI128, NonZeroUsize, NonZeroIsize
+);
+#[rustfmt::skip]
+#[cfg(feature = "float-nightly")]
+impl_known_layout!(
+    #[cfg_attr(doc_cfg, doc(cfg(feature = "float-nightly")))]
+    f16,
+    #[cfg_attr(doc_cfg, doc(cfg(feature = "float-nightly")))]
+    f128
+);
+#[rustfmt::skip]
+impl_known_layout!(
+    T         => Option<T>,
+    T: ?Sized => PhantomData<T>,
+    T         => Wrapping<T>,
+    T         => CoreMaybeUninit<T>,
+    T: ?Sized => *const T,
+    T: ?Sized => *mut T,
+    T: ?Sized => &'_ T,
+    T: ?Sized => &'_ mut T,
+);
+impl_known_layout!(const N: usize, T => [T; N]);
+
+// SAFETY: `str` has the same representation as `[u8]`. `ManuallyDrop<T>` [1],
+// `UnsafeCell<T>` [2], and `Cell<T>` [3] have the same representation as `T`.
+//
+// [1] Per https://doc.rust-lang.org/1.85.0/std/mem/struct.ManuallyDrop.html:
+//
+//   `ManuallyDrop<T>` is guaranteed to have the same layout and bit validity as
+//   `T`
+//
+// [2] Per https://doc.rust-lang.org/1.85.0/core/cell/struct.UnsafeCell.html#memory-layout:
+//
+//   `UnsafeCell<T>` has the same in-memory representation as its inner type
+//   `T`.
+//
+// [3] Per https://doc.rust-lang.org/1.85.0/core/cell/struct.Cell.html#memory-layout:
+//
+//   `Cell<T>` has the same in-memory representation as `T`.
+#[allow(clippy::multiple_unsafe_ops_per_block)]
+const _: () = unsafe {
+    unsafe_impl_known_layout!(
+        #[repr([u8])]
+        str
+    );
+    unsafe_impl_known_layout!(T: ?Sized + KnownLayout => #[repr(T)] ManuallyDrop<T>);
+    unsafe_impl_known_layout!(T: ?Sized + KnownLayout => #[repr(T)] UnsafeCell<T>);
+    unsafe_impl_known_layout!(T: ?Sized + KnownLayout => #[repr(T)] Cell<T>);
+};
+
+// SAFETY:
+// - By consequence of the invariant on `T::MaybeUninit` that `T::LAYOUT` and
+//   `T::MaybeUninit::LAYOUT` are equal, `T` and `T::MaybeUninit` have the same:
+//   - Fixed prefix size
+//   - Alignment
+//   - (For DSTs) trailing slice element size
+// - By consequence of the above, referents `T::MaybeUninit` and `T` have the
+//   require the same kind of pointer metadata, and thus it is valid to perform
+//   an `as` cast from `*mut T` and `*mut T::MaybeUninit`, and this operation
+//   preserves referent size (ie, `size_of_val_raw`).
+const _: () = unsafe {
+    unsafe_impl_known_layout!(T: ?Sized + KnownLayout => #[repr(T::MaybeUninit)] MaybeUninit<T>)
+};
+
+// FIXME(#196, #2856): Eventually, we'll want to support enums variants and
+// union fields being treated uniformly since they behave similarly to each
+// other in terms of projecting validity – specifically, for a type `T` with
+// validity `V`, if `T` is a struct type, then its fields straightforwardly also
+// have validity `V`. By contrast, if `T` is an enum or union type, then
+// validity is not straightforwardly recursive in this way.
+#[doc(hidden)]
+pub const STRUCT_VARIANT_ID: i128 = -1;
+#[doc(hidden)]
+pub const UNION_VARIANT_ID: i128 = -2;
+#[doc(hidden)]
+pub const REPR_C_UNION_VARIANT_ID: i128 = -3;
+
+/// # Safety
+///
+/// `Self::ProjectToTag` must satisfy its safety invariant.
+#[doc(hidden)]
+pub unsafe trait HasTag {
+    fn only_derive_is_allowed_to_implement_this_trait()
+    where
+        Self: Sized;
+
+    /// The type's enum tag, or `()` for non-enum types.
+    type Tag: Immutable;
+
+    /// A pointer projection from `Self` to its tag.
+    ///
+    /// # Safety
+    ///
+    /// It must be the case that, for all `slf: Ptr<'_, Self, I>`, it is sound
+    /// to project from `slf` to `Ptr<'_, Self::Tag, I>` using this projection.
+    type ProjectToTag: pointer::cast::Project<Self, Self::Tag>;
+}
+
+/// Projects a given field from `Self`.
+///
+/// All implementations of `HasField` for a particular field `f` in `Self`
+/// should use the same `Field` type; this ensures that `Field` is inferable
+/// given an explicit `VARIANT_ID` and `FIELD_ID`.
+///
+/// # Safety
+///
+/// A field `f` is `HasField` for `Self` if and only if:
+///
+/// - If `Self` has the layout of a struct or union type, then `VARIANT_ID` is
+///   `STRUCT_VARIANT_ID` or `UNION_VARIANT_ID` respectively; otherwise, if
+///   `Self` has the layout of an enum type, `VARIANT_ID` is the numerical index
+///   of the enum variant in which `f` appears. Note that `Self` does not need
+///   to actually *be* such a type – it just needs to have the same layout as
+///   such a type. For example, a `#[repr(transparent)]` wrapper around an enum
+///   has the same layout as that enum.
+/// - If `f` has name `n`, `FIELD_ID` is `zerocopy::ident_id!(n)`; otherwise,
+///   if `f` is at index `i`, `FIELD_ID` is `zerocopy::ident_id!(i)`.
+/// - `Field` is a type with the same visibility as `f`.
+/// - `Type` has the same type as `f`.
+///
+/// The caller must **not** assume that a pointer's referent being aligned
+/// implies that calling `project` on that pointer will result in a pointer to
+/// an aligned referent. For example, `HasField` may be implemented for
+/// `#[repr(packed)]` structs.
+///
+/// The implementation of `project` must satisfy its safety post-condition.
+#[doc(hidden)]
+pub unsafe trait HasField<Field, const VARIANT_ID: i128, const FIELD_ID: i128>:
+    HasTag
+{
+    fn only_derive_is_allowed_to_implement_this_trait()
+    where
+        Self: Sized;
+
+    /// The type of the field.
+    type Type: ?Sized;
+
+    /// Projects from `slf` to the field.
+    ///
+    /// Users should generally not call `project` directly, and instead should
+    /// use high-level APIs like [`PtrInner::project`] or [`Ptr::project`].
+    ///
+    /// # Safety
+    ///
+    /// The returned pointer refers to a non-strict subset of the bytes of
+    /// `slf`'s referent, and has the same provenance as `slf`.
+    #[must_use]
+    fn project(slf: PtrInner<'_, Self>) -> *mut Self::Type;
+}
+
+/// Projects a given field from `Self`.
+///
+/// Implementations of this trait encode the conditions under which a field can
+/// be projected from a `Ptr<'_, Self, I>`, and how the invariants of that
+/// [`Ptr`] (`I`) determine the invariants of pointers projected from it. In
+/// other words, it is a type-level function over invariants; `I` goes in,
+/// `Self::Invariants` comes out.
+///
+/// # Safety
+///
+/// `T: ProjectField<Field, I, VARIANT_ID, FIELD_ID>` if, for a
+/// `ptr: Ptr<'_, T, I>` such that `T::is_projectable(ptr).is_ok()`,
+/// `<T as HasField<Field, VARIANT_ID, FIELD_ID>>::project(ptr.as_inner())`
+/// conforms to `T::Invariants`.
+#[doc(hidden)]
+pub unsafe trait ProjectField<Field, I, const VARIANT_ID: i128, const FIELD_ID: i128>:
+    HasField<Field, VARIANT_ID, FIELD_ID>
+where
+    I: invariant::Invariants,
+{
+    fn only_derive_is_allowed_to_implement_this_trait()
+    where
+        Self: Sized;
+
+    /// The invariants of the projected field pointer, with respect to the
+    /// invariants, `I`, of the containing pointer. The aliasing dimension of
+    /// the invariants is guaranteed to remain unchanged.
+    type Invariants: invariant::Invariants<Aliasing = I::Aliasing>;
+
+    /// The failure mode of projection. `()` if the projection is fallible,
+    /// otherwise [`core::convert::Infallible`].
+    type Error;
+
+    /// Is the given field projectable from `ptr`?
+    ///
+    /// If a field with [`Self::Invariants`] is projectable from the referent,
+    /// this function produces an `Ok(ptr)` from which the projection can be
+    /// made; otherwise `Err`.
+    ///
+    /// This method must be overriden if the field's projectability depends on
+    /// the value of the bytes in `ptr`.
+    #[inline(always)]
+    fn is_projectable<'a>(_ptr: Ptr<'a, Self::Tag, I>) -> Result<(), Self::Error> {
+        trait IsInfallible {
+            const IS_INFALLIBLE: bool;
+        }
+
+        struct Projection<T, Field, I, const VARIANT_ID: i128, const FIELD_ID: i128>(
+            PhantomData<(Field, I, T)>,
+        )
+        where
+            T: ?Sized + HasField<Field, VARIANT_ID, FIELD_ID>,
+            I: invariant::Invariants;
+
+        impl<T, Field, I, const VARIANT_ID: i128, const FIELD_ID: i128> IsInfallible
+            for Projection<T, Field, I, VARIANT_ID, FIELD_ID>
+        where
+            T: ?Sized + HasField<Field, VARIANT_ID, FIELD_ID>,
+            I: invariant::Invariants,
+        {
+            const IS_INFALLIBLE: bool = {
+                let is_infallible = match VARIANT_ID {
+                    // For nondestructive projections of struct and union
+                    // fields, the projected field's satisfaction of
+                    // `Invariants` does not depend on the value of the
+                    // referent. This default implementation of `is_projectable`
+                    // is non-destructive, as it does not overwrite any part of
+                    // the referent.
+                    crate::STRUCT_VARIANT_ID | crate::UNION_VARIANT_ID => true,
+                    _enum_variant => {
+                        use crate::invariant::{Validity, ValidityKind};
+                        match I::Validity::KIND {
+                            // The `Uninit` and `Initialized` validity
+                            // invariants do not depend on the enum's tag. In
+                            // particular, we don't actually care about what
+                            // variant is present – we can treat *any* range of
+                            // uninitialized or initialized memory as containing
+                            // an uninitialized or initialized instance of *any*
+                            // type – the type itself is irrelevant.
+                            ValidityKind::Uninit | ValidityKind::Initialized => true,
+                            // The projectability of an enum field from an
+                            // `AsInitialized` or `Valid` state is a dynamic
+                            // property of its tag.
+                            ValidityKind::AsInitialized | ValidityKind::Valid => false,
+                        }
+                    }
+                };
+                const_assert!(is_infallible);
+                is_infallible
+            };
+        }
+
+        const_assert!(
+            <Projection<Self, Field, I, VARIANT_ID, FIELD_ID> as IsInfallible>::IS_INFALLIBLE
+        );
+
+        Ok(())
+    }
+}
+
+/// Analyzes whether a type is [`FromZeros`].
+///
+/// This derive analyzes, at compile time, whether the annotated type satisfies
+/// the [safety conditions] of `FromZeros` and implements `FromZeros` and its
+/// supertraits if it is sound to do so. This derive can be applied to structs,
+/// enums, and unions; e.g.:
+///
+/// ```
+/// # use zerocopy_derive::{FromZeros, Immutable};
+/// #[derive(FromZeros)]
+/// struct MyStruct {
+/// # /*
+///     ...
+/// # */
+/// }
+///
+/// #[derive(FromZeros)]
+/// #[repr(u8)]
+/// enum MyEnum {
+/// #   Variant0,
+/// # /*
+///     ...
+/// # */
+/// }
+///
+/// #[derive(FromZeros, Immutable)]
+/// union MyUnion {
+/// #   variant: u8,
+/// # /*
+///     ...
+/// # */
+/// }
+/// ```
+///
+/// [safety conditions]: trait@FromZeros#safety
+///
+/// # Analysis
+///
+/// *This section describes, roughly, the analysis performed by this derive to
+/// determine whether it is sound to implement `FromZeros` for a given type.
+/// Unless you are modifying the implementation of this derive, or attempting to
+/// manually implement `FromZeros` for a type yourself, you don't need to read
+/// this section.*
+///
+/// If a type has the following properties, then this derive can implement
+/// `FromZeros` for that type:
+///
+/// - If the type is a struct, all of its fields must be `FromZeros`.
+/// - If the type is an enum:
+///   - It must have a defined representation (`repr`s `C`, `u8`, `u16`, `u32`,
+///     `u64`, `usize`, `i8`, `i16`, `i32`, `i64`, or `isize`).
+///   - It must have a variant with a discriminant/tag of `0`, and its fields
+///     must be `FromZeros`. See [the reference] for a description of
+///     discriminant values are specified.
+///   - The fields of that variant must be `FromZeros`.
+///
+/// This analysis is subject to change. Unsafe code may *only* rely on the
+/// documented [safety conditions] of `FromZeros`, and must *not* rely on the
+/// implementation details of this derive.
+///
+/// [the reference]: https://doc.rust-lang.org/reference/items/enumerations.html#custom-discriminant-values-for-fieldless-enumerations
+///
+/// ## Why isn't an explicit representation required for structs?
+///
+/// Neither this derive, nor the [safety conditions] of `FromZeros`, requires
+/// that structs are marked with `#[repr(C)]`.
+///
+/// Per the [Rust reference](reference),
+///
+/// > The representation of a type can change the padding between fields, but
+/// > does not change the layout of the fields themselves.
+///
+/// [reference]: https://doc.rust-lang.org/reference/type-layout.html#representations
+///
+/// Since the layout of structs only consists of padding bytes and field bytes,
+/// a struct is soundly `FromZeros` if:
+/// 1. its padding is soundly `FromZeros`, and
+/// 2. its fields are soundly `FromZeros`.
+///
+/// The answer to the first question is always yes: padding bytes do not have
+/// any validity constraints. A [discussion] of this question in the Unsafe Code
+/// Guidelines Working Group concluded that it would be virtually unimaginable
+/// for future versions of rustc to add validity constraints to padding bytes.
+///
+/// [discussion]: https://github.com/rust-lang/unsafe-code-guidelines/issues/174
+///
+/// Whether a struct is soundly `FromZeros` therefore solely depends on whether
+/// its fields are `FromZeros`.
+// FIXME(#146): Document why we don't require an enum to have an explicit `repr`
+// attribute.
+#[cfg(any(feature = "derive", test))]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "derive")))]
+pub use zerocopy_derive::FromZeros;
+/// Analyzes whether a type is [`Immutable`].
+///
+/// This derive analyzes, at compile time, whether the annotated type satisfies
+/// the [safety conditions] of `Immutable` and implements `Immutable` if it is
+/// sound to do so. This derive can be applied to structs, enums, and unions;
+/// e.g.:
+///
+/// ```
+/// # use zerocopy_derive::Immutable;
+/// #[derive(Immutable)]
+/// struct MyStruct {
+/// # /*
+///     ...
+/// # */
+/// }
+///
+/// #[derive(Immutable)]
+/// enum MyEnum {
+/// #   Variant0,
+/// # /*
+///     ...
+/// # */
+/// }
+///
+/// #[derive(Immutable)]
+/// union MyUnion {
+/// #   variant: u8,
+/// # /*
+///     ...
+/// # */
+/// }
+/// ```
+///
+/// # Analysis
+///
+/// *This section describes, roughly, the analysis performed by this derive to
+/// determine whether it is sound to implement `Immutable` for a given type.
+/// Unless you are modifying the implementation of this derive, you don't need
+/// to read this section.*
+///
+/// If a type has the following properties, then this derive can implement
+/// `Immutable` for that type:
+///
+/// - All fields must be `Immutable`.
+///
+/// This analysis is subject to change. Unsafe code may *only* rely on the
+/// documented [safety conditions] of `Immutable`, and must *not* rely on the
+/// implementation details of this derive.
+///
+/// [safety conditions]: trait@Immutable#safety
+#[cfg(any(feature = "derive", test))]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "derive")))]
+pub use zerocopy_derive::Immutable;
+
+/// Types which are free from interior mutability.
+///
+/// `T: Immutable` indicates that `T` does not permit interior mutation, except
+/// by ownership or an exclusive (`&mut`) borrow.
+///
+/// # Implementation
+///
+/// **Do not implement this trait yourself!** Instead, use
+/// [`#[derive(Immutable)]`][derive] (requires the `derive` Cargo feature);
+/// e.g.:
+///
+/// ```
+/// # use zerocopy_derive::Immutable;
+/// #[derive(Immutable)]
+/// struct MyStruct {
+/// # /*
+///     ...
+/// # */
+/// }
+///
+/// #[derive(Immutable)]
+/// enum MyEnum {
+/// # /*
+///     ...
+/// # */
+/// }
+///
+/// #[derive(Immutable)]
+/// union MyUnion {
+/// #   variant: u8,
+/// # /*
+///     ...
+/// # */
+/// }
+/// ```
+///
+/// This derive performs a sophisticated, compile-time safety analysis to
+/// determine whether a type is `Immutable`.
+///
+/// # Safety
+///
+/// Unsafe code outside of this crate must not make any assumptions about `T`
+/// based on `T: Immutable`. We reserve the right to relax the requirements for
+/// `Immutable` in the future, and if unsafe code outside of this crate makes
+/// assumptions based on `T: Immutable`, future relaxations may cause that code
+/// to become unsound.
+///
+// # Safety (Internal)
+//
+// If `T: Immutable`, unsafe code *inside of this crate* may assume that, given
+// `t: &T`, `t` does not permit interior mutation of its referent. Because
+// [`UnsafeCell`] is the only type which permits interior mutation, it is
+// sufficient (though not necessary) to guarantee that `T` contains no
+// `UnsafeCell`s.
+//
+// [`UnsafeCell`]: core::cell::UnsafeCell
+#[cfg_attr(
+    feature = "derive",
+    doc = "[derive]: zerocopy_derive::Immutable",
+    doc = "[derive-analysis]: zerocopy_derive::Immutable#analysis"
+)]
+#[cfg_attr(
+    not(feature = "derive"),
+    doc = concat!("[derive]: https://docs.rs/zerocopy/", env!("CARGO_PKG_VERSION"), "/zerocopy/derive.Immutable.html"),
+    doc = concat!("[derive-analysis]: https://docs.rs/zerocopy/", env!("CARGO_PKG_VERSION"), "/zerocopy/derive.Immutable.html#analysis"),
+)]
+#[cfg_attr(
+    not(no_zerocopy_diagnostic_on_unimplemented_1_78_0),
+    diagnostic::on_unimplemented(note = "Consider adding `#[derive(Immutable)]` to `{Self}`")
+)]
+pub unsafe trait Immutable {
+    // The `Self: Sized` bound makes it so that `Immutable` is still object
+    // safe.
+    #[doc(hidden)]
+    fn only_derive_is_allowed_to_implement_this_trait()
+    where
+        Self: Sized;
+}
+
+/// Implements [`TryFromBytes`].
+///
+/// This derive synthesizes the runtime checks required to check whether a
+/// sequence of initialized bytes corresponds to a valid instance of a type.
+/// This derive can be applied to structs, enums, and unions; e.g.:
+///
+/// ```
+/// # use zerocopy_derive::{TryFromBytes, Immutable};
+/// #[derive(TryFromBytes)]
+/// struct MyStruct {
+/// # /*
+///     ...
+/// # */
+/// }
+///
+/// #[derive(TryFromBytes)]
+/// #[repr(u8)]
+/// enum MyEnum {
+/// #   V00,
+/// # /*
+///     ...
+/// # */
+/// }
+///
+/// #[derive(TryFromBytes, Immutable)]
+/// union MyUnion {
+/// #   variant: u8,
+/// # /*
+///     ...
+/// # */
+/// }
+/// ```
+///
+/// # Portability
+///
+/// To ensure consistent endianness for enums with multi-byte representations,
+/// explicitly specify and convert each discriminant using `.to_le()` or
+/// `.to_be()`; e.g.:
+///
+/// ```
+/// # use zerocopy_derive::TryFromBytes;
+/// // `DataStoreVersion` is encoded in little-endian.
+/// #[derive(TryFromBytes)]
+/// #[repr(u32)]
+/// pub enum DataStoreVersion {
+///     /// Version 1 of the data store.
+///     V1 = 9u32.to_le(),
+///
+///     /// Version 2 of the data store.
+///     V2 = 10u32.to_le(),
+/// }
+/// ```
+///
+/// [safety conditions]: trait@TryFromBytes#safety
+#[cfg(any(feature = "derive", test))]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "derive")))]
+pub use zerocopy_derive::TryFromBytes;
+
+/// Types for which some bit patterns are valid.
+///
+/// A memory region of the appropriate length which contains initialized bytes
+/// can be viewed as a `TryFromBytes` type so long as the runtime value of those
+/// bytes corresponds to a [*valid instance*] of that type. For example,
+/// [`bool`] is `TryFromBytes`, so zerocopy can transmute a [`u8`] into a
+/// [`bool`] so long as it first checks that the value of the [`u8`] is `0` or
+/// `1`.
+///
+/// # Implementation
+///
+/// **Do not implement this trait yourself!** Instead, use
+/// [`#[derive(TryFromBytes)]`][derive]; e.g.:
+///
+/// ```
+/// # use zerocopy_derive::{TryFromBytes, Immutable};
+/// #[derive(TryFromBytes)]
+/// struct MyStruct {
+/// # /*
+///     ...
+/// # */
+/// }
+///
+/// #[derive(TryFromBytes)]
+/// #[repr(u8)]
+/// enum MyEnum {
+/// #   V00,
+/// # /*
+///     ...
+/// # */
+/// }
+///
+/// #[derive(TryFromBytes, Immutable)]
+/// union MyUnion {
+/// #   variant: u8,
+/// # /*
+///     ...
+/// # */
+/// }
+/// ```
+///
+/// This derive ensures that the runtime check of whether bytes correspond to a
+/// valid instance is sound. You **must** implement this trait via the derive.
+///
+/// # What is a "valid instance"?
+///
+/// In Rust, each type has *bit validity*, which refers to the set of bit
+/// patterns which may appear in an instance of that type. It is impossible for
+/// safe Rust code to produce values which violate bit validity (ie, values
+/// outside of the "valid" set of bit patterns). If `unsafe` code produces an
+/// invalid value, this is considered [undefined behavior].
+///
+/// Rust's bit validity rules are currently being decided, which means that some
+/// types have three classes of bit patterns: those which are definitely valid,
+/// and whose validity is documented in the language; those which may or may not
+/// be considered valid at some point in the future; and those which are
+/// definitely invalid.
+///
+/// Zerocopy takes a conservative approach, and only considers a bit pattern to
+/// be valid if its validity is a documented guarantee provided by the
+/// language.
+///
+/// For most use cases, Rust's current guarantees align with programmers'
+/// intuitions about what ought to be valid. As a result, zerocopy's
+/// conservatism should not affect most users.
+///
+/// If you are negatively affected by lack of support for a particular type,
+/// we encourage you to let us know by [filing an issue][github-repo].
+///
+/// # `TryFromBytes` is not symmetrical with [`IntoBytes`]
+///
+/// There are some types which implement both `TryFromBytes` and [`IntoBytes`],
+/// but for which `TryFromBytes` is not guaranteed to accept all byte sequences
+/// produced by `IntoBytes`. In other words, for some `T: TryFromBytes +
+/// IntoBytes`, there exist values of `t: T` such that
+/// `TryFromBytes::try_ref_from_bytes(t.as_bytes()) == None`. Code should not
+/// generally assume that values produced by `IntoBytes` will necessarily be
+/// accepted as valid by `TryFromBytes`.
+///
+/// # Safety
+///
+/// On its own, `T: TryFromBytes` does not make any guarantees about the layout
+/// or representation of `T`. It merely provides the ability to perform a
+/// validity check at runtime via methods like [`try_ref_from_bytes`].
+///
+/// You must not rely on the `#[doc(hidden)]` internals of `TryFromBytes`.
+/// Future releases of zerocopy may make backwards-breaking changes to these
+/// items, including changes that only affect soundness, which may cause code
+/// which uses those items to silently become unsound.
+///
+/// [undefined behavior]: https://raphlinus.github.io/programming/rust/2018/08/17/undefined-behavior.html
+/// [github-repo]: https://github.com/google/zerocopy
+/// [`try_ref_from_bytes`]: TryFromBytes::try_ref_from_bytes
+/// [*valid instance*]: #what-is-a-valid-instance
+#[cfg_attr(feature = "derive", doc = "[derive]: zerocopy_derive::TryFromBytes")]
+#[cfg_attr(
+    not(feature = "derive"),
+    doc = concat!("[derive]: https://docs.rs/zerocopy/", env!("CARGO_PKG_VERSION"), "/zerocopy/derive.TryFromBytes.html"),
+)]
+#[cfg_attr(
+    not(no_zerocopy_diagnostic_on_unimplemented_1_78_0),
+    diagnostic::on_unimplemented(note = "Consider adding `#[derive(TryFromBytes)]` to `{Self}`")
+)]
+pub unsafe trait TryFromBytes {
+    // The `Self: Sized` bound makes it so that `TryFromBytes` is still object
+    // safe.
+    #[doc(hidden)]
+    fn only_derive_is_allowed_to_implement_this_trait()
+    where
+        Self: Sized;
+
+    /// Does a given memory range contain a valid instance of `Self`?
+    ///
+    /// # Safety
+    ///
+    /// Unsafe code may assume that, if `is_bit_valid(candidate)` returns true,
+    /// `*candidate` contains a valid `Self`.
+    ///
+    /// # Panics
+    ///
+    /// `is_bit_valid` may panic. Callers are responsible for ensuring that any
+    /// `unsafe` code remains sound even in the face of `is_bit_valid`
+    /// panicking. (We support user-defined validation routines; so long as
+    /// these routines are not required to be `unsafe`, there is no way to
+    /// ensure that these do not generate panics.)
+    ///
+    /// Besides user-defined validation routines panicking, `is_bit_valid` will
+    /// either panic or fail to compile if called on a pointer with [`Shared`]
+    /// aliasing when `Self: !Immutable`.
+    ///
+    /// [`UnsafeCell`]: core::cell::UnsafeCell
+    /// [`Shared`]: invariant::Shared
+    #[doc(hidden)]
+    fn is_bit_valid<A>(candidate: Maybe<'_, Self, A>) -> bool
+    where
+        A: invariant::Alignment;
+
+    /// Attempts to interpret the given `source` as a `&Self`.
+    ///
+    /// If the bytes of `source` are a valid instance of `Self`, this method
+    /// returns a reference to those bytes interpreted as a `Self`. If the
+    /// length of `source` is not a [valid size of `Self`][valid-size], or if
+    /// `source` is not appropriately aligned, or if `source` is not a valid
+    /// instance of `Self`, this returns `Err`. If [`Self:
+    /// Unaligned`][self-unaligned], you can [infallibly discard the alignment
+    /// error][ConvertError::from].
+    ///
+    /// `Self` may be a sized type, a slice, or a [slice DST][slice-dst].
+    ///
+    /// [valid-size]: crate::KnownLayout#what-is-a-valid-size
+    /// [self-unaligned]: Unaligned
+    /// [slice-dst]: KnownLayout#dynamically-sized-types
+    ///
+    /// # Compile-Time Assertions
+    ///
+    /// This method cannot yet be used on unsized types whose dynamically-sized
+    /// component is zero-sized. Attempting to use this method on such types
+    /// results in a compile-time assertion error; e.g.:
+    ///
+    /// ```compile_fail,E0080
+    /// use zerocopy::*;
+    /// # use zerocopy_derive::*;
+    ///
+    /// #[derive(TryFromBytes, Immutable, KnownLayout)]
+    /// #[repr(C)]
+    /// struct ZSTy {
+    ///     leading_sized: u16,
+    ///     trailing_dst: [()],
+    /// }
+    ///
+    /// let _ = ZSTy::try_ref_from_bytes(0u16.as_bytes()); // ⚠ Compile Error!
+    /// ```
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use zerocopy::TryFromBytes;
+    /// # use zerocopy_derive::*;
+    ///
+    /// // The only valid value of this type is the byte `0xC0`
+    /// #[derive(TryFromBytes, KnownLayout, Immutable)]
+    /// #[repr(u8)]
+    /// enum C0 { xC0 = 0xC0 }
+    ///
+    /// // The only valid value of this type is the byte sequence `0xC0C0`.
+    /// #[derive(TryFromBytes, KnownLayout, Immutable)]
+    /// #[repr(C)]
+    /// struct C0C0(C0, C0);
+    ///
+    /// #[derive(TryFromBytes, KnownLayout, Immutable)]
+    /// #[repr(C)]
+    /// struct Packet {
+    ///     magic_number: C0C0,
+    ///     mug_size: u8,
+    ///     temperature: u8,
+    ///     marshmallows: [[u8; 2]],
+    /// }
+    ///
+    /// let bytes = &[0xC0, 0xC0, 240, 77, 0, 1, 2, 3, 4, 5][..];
+    ///
+    /// let packet = Packet::try_ref_from_bytes(bytes).unwrap();
+    ///
+    /// assert_eq!(packet.mug_size, 240);
+    /// assert_eq!(packet.temperature, 77);
+    /// assert_eq!(packet.marshmallows, [[0, 1], [2, 3], [4, 5]]);
+    ///
+    /// // These bytes are not valid instance of `Packet`.
+    /// let bytes = &[0x10, 0xC0, 240, 77, 0, 1, 2, 3, 4, 5][..];
+    /// assert!(Packet::try_ref_from_bytes(bytes).is_err());
+    /// ```
+    ///
+    #[doc = codegen_section!(
+        header = "h5",
+        bench = "try_ref_from_bytes",
+        format = "coco",
+        arity = 3,
+        [
+            open
+            @index 1
+            @title "Sized"
+            @variant "static_size"
+        ],
+        [
+            @index 2
+            @title "Unsized"
+            @variant "dynamic_size"
+        ],
+        [
+            @index 3
+            @title "Dynamically Padded"
+            @variant "dynamic_padding"
+        ]
+    )]
+    #[must_use = "has no side effects"]
+    #[cfg_attr(zerocopy_inline_always, inline(always))]
+    #[cfg_attr(not(zerocopy_inline_always), inline)]
+    fn try_ref_from_bytes(source: &[u8]) -> Result<&Self, TryCastError<&[u8], Self>>
+    where
+        Self: KnownLayout + Immutable,
+    {
+        static_assert_dst_is_not_zst!(Self);
+        match Ptr::from_ref(source).try_cast_into_no_leftover::<Self, BecauseImmutable>(None) {
+            Ok(source) => {
+                // This call may panic. If that happens, it doesn't cause any soundness
+                // issues, as we have not generated any invalid state which we need to
+                // fix before returning.
+                match source.try_into_valid() {
+                    Ok(valid) => Ok(valid.as_ref()),
+                    Err(e) => {
+                        Err(e.map_src(|src| src.as_bytes::<BecauseImmutable>().as_ref()).into())
+                    }
+                }
+            }
+            Err(e) => Err(e.map_src(Ptr::as_ref).into()),
+        }
+    }
+
+    /// Attempts to interpret the prefix of the given `source` as a `&Self`.
+    ///
+    /// This method computes the [largest possible size of `Self`][valid-size]
+    /// that can fit in the leading bytes of `source`. If that prefix is a valid
+    /// instance of `Self`, this method returns a reference to those bytes
+    /// interpreted as `Self`, and a reference to the remaining bytes. If there
+    /// are insufficient bytes, or if `source` is not appropriately aligned, or
+    /// if those bytes are not a valid instance of `Self`, this returns `Err`.
+    /// If [`Self: Unaligned`][self-unaligned], you can [infallibly discard the
+    /// alignment error][ConvertError::from].
+    ///
+    /// `Self` may be a sized type, a slice, or a [slice DST][slice-dst].
+    ///
+    /// [valid-size]: crate::KnownLayout#what-is-a-valid-size
+    /// [self-unaligned]: Unaligned
+    /// [slice-dst]: KnownLayout#dynamically-sized-types
+    ///
+    /// # Compile-Time Assertions
+    ///
+    /// This method cannot yet be used on unsized types whose dynamically-sized
+    /// component is zero-sized. Attempting to use this method on such types
+    /// results in a compile-time assertion error; e.g.:
+    ///
+    /// ```compile_fail,E0080
+    /// use zerocopy::*;
+    /// # use zerocopy_derive::*;
+    ///
+    /// #[derive(TryFromBytes, Immutable, KnownLayout)]
+    /// #[repr(C)]
+    /// struct ZSTy {
+    ///     leading_sized: u16,
+    ///     trailing_dst: [()],
+    /// }
+    ///
+    /// let _ = ZSTy::try_ref_from_prefix(0u16.as_bytes()); // ⚠ Compile Error!
+    /// ```
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use zerocopy::TryFromBytes;
+    /// # use zerocopy_derive::*;
+    ///
+    /// // The only valid value of this type is the byte `0xC0`
+    /// #[derive(TryFromBytes, KnownLayout, Immutable)]
+    /// #[repr(u8)]
+    /// enum C0 { xC0 = 0xC0 }
+    ///
+    /// // The only valid value of this type is the bytes `0xC0C0`.
+    /// #[derive(TryFromBytes, KnownLayout, Immutable)]
+    /// #[repr(C)]
+    /// struct C0C0(C0, C0);
+    ///
+    /// #[derive(TryFromBytes, KnownLayout, Immutable)]
+    /// #[repr(C)]
+    /// struct Packet {
+    ///     magic_number: C0C0,
+    ///     mug_size: u8,
+    ///     temperature: u8,
+    ///     marshmallows: [[u8; 2]],
+    /// }
+    ///
+    /// // These are more bytes than are needed to encode a `Packet`.
+    /// let bytes = &[0xC0, 0xC0, 240, 77, 0, 1, 2, 3, 4, 5, 6][..];
+    ///
+    /// let (packet, suffix) = Packet::try_ref_from_prefix(bytes).unwrap();
+    ///
+    /// assert_eq!(packet.mug_size, 240);
+    /// assert_eq!(packet.temperature, 77);
+    /// assert_eq!(packet.marshmallows, [[0, 1], [2, 3], [4, 5]]);
+    /// assert_eq!(suffix, &[6u8][..]);
+    ///
+    /// // These bytes are not valid instance of `Packet`.
+    /// let bytes = &[0x10, 0xC0, 240, 77, 0, 1, 2, 3, 4, 5, 6][..];
+    /// assert!(Packet::try_ref_from_prefix(bytes).is_err());
+    /// ```
+    ///
+    #[doc = codegen_section!(
+        header = "h5",
+        bench = "try_ref_from_prefix",
+        format = "coco",
+        arity = 3,
+        [
+            open
+            @index 1
+            @title "Sized"
+            @variant "static_size"
+        ],
+        [
+            @index 2
+            @title "Unsized"
+            @variant "dynamic_size"
+        ],
+        [
+            @index 3
+            @title "Dynamically Padded"
+            @variant "dynamic_padding"
+        ]
+    )]
+    #[must_use = "has no side effects"]
+    #[cfg_attr(zerocopy_inline_always, inline(always))]
+    #[cfg_attr(not(zerocopy_inline_always), inline)]
+    fn try_ref_from_prefix(source: &[u8]) -> Result<(&Self, &[u8]), TryCastError<&[u8], Self>>
+    where
+        Self: KnownLayout + Immutable,
+    {
+        static_assert_dst_is_not_zst!(Self);
+        try_ref_from_prefix_suffix(source, CastType::Prefix, None)
+    }
+
+    /// Attempts to interpret the suffix of the given `source` as a `&Self`.
+    ///
+    /// This method computes the [largest possible size of `Self`][valid-size]
+    /// that can fit in the trailing bytes of `source`. If that suffix is a
+    /// valid instance of `Self`, this method returns a reference to those bytes
+    /// interpreted as `Self`, and a reference to the preceding bytes. If there
+    /// are insufficient bytes, or if the suffix of `source` would not be
+    /// appropriately aligned, or if the suffix is not a valid instance of
+    /// `Self`, this returns `Err`. If [`Self: Unaligned`][self-unaligned], you
+    /// can [infallibly discard the alignment error][ConvertError::from].
+    ///
+    /// `Self` may be a sized type, a slice, or a [slice DST][slice-dst].
+    ///
+    /// [valid-size]: crate::KnownLayout#what-is-a-valid-size
+    /// [self-unaligned]: Unaligned
+    /// [slice-dst]: KnownLayout#dynamically-sized-types
+    ///
+    /// # Compile-Time Assertions
+    ///
+    /// This method cannot yet be used on unsized types whose dynamically-sized
+    /// component is zero-sized. Attempting to use this method on such types
+    /// results in a compile-time assertion error; e.g.:
+    ///
+    /// ```compile_fail,E0080
+    /// use zerocopy::*;
+    /// # use zerocopy_derive::*;
+    ///
+    /// #[derive(TryFromBytes, Immutable, KnownLayout)]
+    /// #[repr(C)]
+    /// struct ZSTy {
+    ///     leading_sized: u16,
+    ///     trailing_dst: [()],
+    /// }
+    ///
+    /// let _ = ZSTy::try_ref_from_suffix(0u16.as_bytes()); // ⚠ Compile Error!
+    /// ```
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use zerocopy::TryFromBytes;
+    /// # use zerocopy_derive::*;
+    ///
+    /// // The only valid value of this type is the byte `0xC0`
+    /// #[derive(TryFromBytes, KnownLayout, Immutable)]
+    /// #[repr(u8)]
+    /// enum C0 { xC0 = 0xC0 }
+    ///
+    /// // The only valid value of this type is the bytes `0xC0C0`.
+    /// #[derive(TryFromBytes, KnownLayout, Immutable)]
+    /// #[repr(C)]
+    /// struct C0C0(C0, C0);
+    ///
+    /// #[derive(TryFromBytes, KnownLayout, Immutable)]
+    /// #[repr(C)]
+    /// struct Packet {
+    ///     magic_number: C0C0,
+    ///     mug_size: u8,
+    ///     temperature: u8,
+    ///     marshmallows: [[u8; 2]],
+    /// }
+    ///
+    /// // These are more bytes than are needed to encode a `Packet`.
+    /// let bytes = &[0, 0xC0, 0xC0, 240, 77, 2, 3, 4, 5, 6, 7][..];
+    ///
+    /// let (prefix, packet) = Packet::try_ref_from_suffix(bytes).unwrap();
+    ///
+    /// assert_eq!(packet.mug_size, 240);
+    /// assert_eq!(packet.temperature, 77);
+    /// assert_eq!(packet.marshmallows, [[2, 3], [4, 5], [6, 7]]);
+    /// assert_eq!(prefix, &[0u8][..]);
+    ///
+    /// // These bytes are not valid instance of `Packet`.
+    /// let bytes = &[0, 1, 2, 3, 4, 5, 6, 77, 240, 0xC0, 0x10][..];
+    /// assert!(Packet::try_ref_from_suffix(bytes).is_err());
+    /// ```
+    ///
+    #[doc = codegen_section!(
+        header = "h5",
+        bench = "try_ref_from_suffix",
+        format = "coco",
+        arity = 3,
+        [
+            open
+            @index 1
+            @title "Sized"
+            @variant "static_size"
+        ],
+        [
+            @index 2
+            @title "Unsized"
+            @variant "dynamic_size"
+        ],
+        [
+            @index 3
+            @title "Dynamically Padded"
+            @variant "dynamic_padding"
+        ]
+    )]
+    #[must_use = "has no side effects"]
+    #[cfg_attr(zerocopy_inline_always, inline(always))]
+    #[cfg_attr(not(zerocopy_inline_always), inline)]
+    fn try_ref_from_suffix(source: &[u8]) -> Result<(&[u8], &Self), TryCastError<&[u8], Self>>
+    where
+        Self: KnownLayout + Immutable,
+    {
+        static_assert_dst_is_not_zst!(Self);
+        try_ref_from_prefix_suffix(source, CastType::Suffix, None).map(swap)
+    }
+
+    /// Attempts to interpret the given `source` as a `&mut Self` without
+    /// copying.
+    ///
+    /// If the bytes of `source` are a valid instance of `Self`, this method
+    /// returns a reference to those bytes interpreted as a `Self`. If the
+    /// length of `source` is not a [valid size of `Self`][valid-size], or if
+    /// `source` is not appropriately aligned, or if `source` is not a valid
+    /// instance of `Self`, this returns `Err`. If [`Self:
+    /// Unaligned`][self-unaligned], you can [infallibly discard the alignment
+    /// error][ConvertError::from].
+    ///
+    /// `Self` may be a sized type, a slice, or a [slice DST][slice-dst].
+    ///
+    /// [valid-size]: crate::KnownLayout#what-is-a-valid-size
+    /// [self-unaligned]: Unaligned
+    /// [slice-dst]: KnownLayout#dynamically-sized-types
+    ///
+    /// # Compile-Time Assertions
+    ///
+    /// This method cannot yet be used on unsized types whose dynamically-sized
+    /// component is zero-sized. Attempting to use this method on such types
+    /// results in a compile-time assertion error; e.g.:
+    ///
+    /// ```compile_fail,E0080
+    /// use zerocopy::*;
+    /// # use zerocopy_derive::*;
+    ///
+    /// #[derive(TryFromBytes, IntoBytes, KnownLayout)]
+    /// #[repr(C, packed)]
+    /// struct ZSTy {
+    ///     leading_sized: [u8; 2],
+    ///     trailing_dst: [()],
+    /// }
+    ///
+    /// let mut source = [85, 85];
+    /// let _ = ZSTy::try_mut_from_bytes(&mut source[..]); // ⚠ Compile Error!
+    /// ```
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use zerocopy::TryFromBytes;
+    /// # use zerocopy_derive::*;
+    ///
+    /// // The only valid value of this type is the byte `0xC0`
+    /// #[derive(TryFromBytes, IntoBytes, KnownLayout)]
+    /// #[repr(u8)]
+    /// enum C0 { xC0 = 0xC0 }
+    ///
+    /// // The only valid value of this type is the bytes `0xC0C0`.
+    /// #[derive(TryFromBytes, IntoBytes, KnownLayout)]
+    /// #[repr(C)]
+    /// struct C0C0(C0, C0);
+    ///
+    /// #[derive(TryFromBytes, IntoBytes, KnownLayout)]
+    /// #[repr(C, packed)]
+    /// struct Packet {
+    ///     magic_number: C0C0,
+    ///     mug_size: u8,
+    ///     temperature: u8,
+    ///     marshmallows: [[u8; 2]],
+    /// }
+    ///
+    /// let bytes = &mut [0xC0, 0xC0, 240, 77, 0, 1, 2, 3, 4, 5][..];
+    ///
+    /// let packet = Packet::try_mut_from_bytes(bytes).unwrap();
+    ///
+    /// assert_eq!(packet.mug_size, 240);
+    /// assert_eq!(packet.temperature, 77);
+    /// assert_eq!(packet.marshmallows, [[0, 1], [2, 3], [4, 5]]);
+    ///
+    /// packet.temperature = 111;
+    ///
+    /// assert_eq!(bytes, [0xC0, 0xC0, 240, 111, 0, 1, 2, 3, 4, 5]);
+    ///
+    /// // These bytes are not valid instance of `Packet`.
+    /// let bytes = &mut [0x10, 0xC0, 240, 77, 0, 1, 2, 3, 4, 5, 6][..];
+    /// assert!(Packet::try_mut_from_bytes(bytes).is_err());
+    /// ```
+    ///
+    #[doc = codegen_header!("h5", "try_mut_from_bytes")]
+    ///
+    /// See [`TryFromBytes::try_ref_from_bytes`](#method.try_ref_from_bytes.codegen).
+    #[must_use = "has no side effects"]
+    #[cfg_attr(zerocopy_inline_always, inline(always))]
+    #[cfg_attr(not(zerocopy_inline_always), inline)]
+    fn try_mut_from_bytes(bytes: &mut [u8]) -> Result<&mut Self, TryCastError<&mut [u8], Self>>
+    where
+        Self: KnownLayout + IntoBytes,
+    {
+        static_assert_dst_is_not_zst!(Self);
+        match Ptr::from_mut(bytes).try_cast_into_no_leftover::<Self, BecauseExclusive>(None) {
+            Ok(source) => {
+                // This call may panic. If that happens, it doesn't cause any soundness
+                // issues, as we have not generated any invalid state which we need to
+                // fix before returning.
+                match source.try_into_valid() {
+                    Ok(source) => Ok(source.as_mut()),
+                    Err(e) => Err(e.map_src(|src| src.as_bytes().as_mut()).into()),
+                }
+            }
+            Err(e) => Err(e.map_src(Ptr::as_mut).into()),
+        }
+    }
+
+    /// Attempts to interpret the prefix of the given `source` as a `&mut
+    /// Self`.
+    ///
+    /// This method computes the [largest possible size of `Self`][valid-size]
+    /// that can fit in the leading bytes of `source`. If that prefix is a valid
+    /// instance of `Self`, this method returns a reference to those bytes
+    /// interpreted as `Self`, and a reference to the remaining bytes. If there
+    /// are insufficient bytes, or if `source` is not appropriately aligned, or
+    /// if the bytes are not a valid instance of `Self`, this returns `Err`. If
+    /// [`Self: Unaligned`][self-unaligned], you can [infallibly discard the
+    /// alignment error][ConvertError::from].
+    ///
+    /// `Self` may be a sized type, a slice, or a [slice DST][slice-dst].
+    ///
+    /// [valid-size]: crate::KnownLayout#what-is-a-valid-size
+    /// [self-unaligned]: Unaligned
+    /// [slice-dst]: KnownLayout#dynamically-sized-types
+    ///
+    /// # Compile-Time Assertions
+    ///
+    /// This method cannot yet be used on unsized types whose dynamically-sized
+    /// component is zero-sized. Attempting to use this method on such types
+    /// results in a compile-time assertion error; e.g.:
+    ///
+    /// ```compile_fail,E0080
+    /// use zerocopy::*;
+    /// # use zerocopy_derive::*;
+    ///
+    /// #[derive(TryFromBytes, IntoBytes, KnownLayout)]
+    /// #[repr(C, packed)]
+    /// struct ZSTy {
+    ///     leading_sized: [u8; 2],
+    ///     trailing_dst: [()],
+    /// }
+    ///
+    /// let mut source = [85, 85];
+    /// let _ = ZSTy::try_mut_from_prefix(&mut source[..]); // ⚠ Compile Error!
+    /// ```
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use zerocopy::TryFromBytes;
+    /// # use zerocopy_derive::*;
+    ///
+    /// // The only valid value of this type is the byte `0xC0`
+    /// #[derive(TryFromBytes, IntoBytes, KnownLayout)]
+    /// #[repr(u8)]
+    /// enum C0 { xC0 = 0xC0 }
+    ///
+    /// // The only valid value of this type is the bytes `0xC0C0`.
+    /// #[derive(TryFromBytes, IntoBytes, KnownLayout)]
+    /// #[repr(C)]
+    /// struct C0C0(C0, C0);
+    ///
+    /// #[derive(TryFromBytes, IntoBytes, KnownLayout)]
+    /// #[repr(C, packed)]
+    /// struct Packet {
+    ///     magic_number: C0C0,
+    ///     mug_size: u8,
+    ///     temperature: u8,
+    ///     marshmallows: [[u8; 2]],
+    /// }
+    ///
+    /// // These are more bytes than are needed to encode a `Packet`.
+    /// let bytes = &mut [0xC0, 0xC0, 240, 77, 0, 1, 2, 3, 4, 5, 6][..];
+    ///
+    /// let (packet, suffix) = Packet::try_mut_from_prefix(bytes).unwrap();
+    ///
+    /// assert_eq!(packet.mug_size, 240);
+    /// assert_eq!(packet.temperature, 77);
+    /// assert_eq!(packet.marshmallows, [[0, 1], [2, 3], [4, 5]]);
+    /// assert_eq!(suffix, &[6u8][..]);
+    ///
+    /// packet.temperature = 111;
+    /// suffix[0] = 222;
+    ///
+    /// assert_eq!(bytes, [0xC0, 0xC0, 240, 111, 0, 1, 2, 3, 4, 5, 222]);
+    ///
+    /// // These bytes are not valid instance of `Packet`.
+    /// let bytes = &mut [0x10, 0xC0, 240, 77, 0, 1, 2, 3, 4, 5, 6][..];
+    /// assert!(Packet::try_mut_from_prefix(bytes).is_err());
+    /// ```
+    ///
+    #[doc = codegen_header!("h5", "try_mut_from_prefix")]
+    ///
+    /// See [`TryFromBytes::try_ref_from_prefix`](#method.try_ref_from_prefix.codegen).
+    #[must_use = "has no side effects"]
+    #[cfg_attr(zerocopy_inline_always, inline(always))]
+    #[cfg_attr(not(zerocopy_inline_always), inline)]
+    fn try_mut_from_prefix(
+        source: &mut [u8],
+    ) -> Result<(&mut Self, &mut [u8]), TryCastError<&mut [u8], Self>>
+    where
+        Self: KnownLayout + IntoBytes,
+    {
+        static_assert_dst_is_not_zst!(Self);
+        try_mut_from_prefix_suffix(source, CastType::Prefix, None)
+    }
+
+    /// Attempts to interpret the suffix of the given `source` as a `&mut
+    /// Self`.
+    ///
+    /// This method computes the [largest possible size of `Self`][valid-size]
+    /// that can fit in the trailing bytes of `source`. If that suffix is a
+    /// valid instance of `Self`, this method returns a reference to those bytes
+    /// interpreted as `Self`, and a reference to the preceding bytes. If there
+    /// are insufficient bytes, or if the suffix of `source` would not be
+    /// appropriately aligned, or if the suffix is not a valid instance of
+    /// `Self`, this returns `Err`. If [`Self: Unaligned`][self-unaligned], you
+    /// can [infallibly discard the alignment error][ConvertError::from].
+    ///
+    /// `Self` may be a sized type, a slice, or a [slice DST][slice-dst].
+    ///
+    /// [valid-size]: crate::KnownLayout#what-is-a-valid-size
+    /// [self-unaligned]: Unaligned
+    /// [slice-dst]: KnownLayout#dynamically-sized-types
+    ///
+    /// # Compile-Time Assertions
+    ///
+    /// This method cannot yet be used on unsized types whose dynamically-sized
+    /// component is zero-sized. Attempting to use this method on such types
+    /// results in a compile-time assertion error; e.g.:
+    ///
+    /// ```compile_fail,E0080
+    /// use zerocopy::*;
+    /// # use zerocopy_derive::*;
+    ///
+    /// #[derive(TryFromBytes, IntoBytes, KnownLayout)]
+    /// #[repr(C, packed)]
+    /// struct ZSTy {
+    ///     leading_sized: u16,
+    ///     trailing_dst: [()],
+    /// }
+    ///
+    /// let mut source = [85, 85];
+    /// let _ = ZSTy::try_mut_from_suffix(&mut source[..]); // ⚠ Compile Error!
+    /// ```
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use zerocopy::TryFromBytes;
+    /// # use zerocopy_derive::*;
+    ///
+    /// // The only valid value of this type is the byte `0xC0`
+    /// #[derive(TryFromBytes, IntoBytes, KnownLayout)]
+    /// #[repr(u8)]
+    /// enum C0 { xC0 = 0xC0 }
+    ///
+    /// // The only valid value of this type is the bytes `0xC0C0`.
+    /// #[derive(TryFromBytes, IntoBytes, KnownLayout)]
+    /// #[repr(C)]
+    /// struct C0C0(C0, C0);
+    ///
+    /// #[derive(TryFromBytes, IntoBytes, KnownLayout)]
+    /// #[repr(C, packed)]
+    /// struct Packet {
+    ///     magic_number: C0C0,
+    ///     mug_size: u8,
+    ///     temperature: u8,
+    ///     marshmallows: [[u8; 2]],
+    /// }
+    ///
+    /// // These are more bytes than are needed to encode a `Packet`.
+    /// let bytes = &mut [0, 0xC0, 0xC0, 240, 77, 2, 3, 4, 5, 6, 7][..];
+    ///
+    /// let (prefix, packet) = Packet::try_mut_from_suffix(bytes).unwrap();
+    ///
+    /// assert_eq!(packet.mug_size, 240);
+    /// assert_eq!(packet.temperature, 77);
+    /// assert_eq!(packet.marshmallows, [[2, 3], [4, 5], [6, 7]]);
+    /// assert_eq!(prefix, &[0u8][..]);
+    ///
+    /// prefix[0] = 111;
+    /// packet.temperature = 222;
+    ///
+    /// assert_eq!(bytes, [111, 0xC0, 0xC0, 240, 222, 2, 3, 4, 5, 6, 7]);
+    ///
+    /// // These bytes are not valid instance of `Packet`.
+    /// let bytes = &mut [0, 1, 2, 3, 4, 5, 6, 77, 240, 0xC0, 0x10][..];
+    /// assert!(Packet::try_mut_from_suffix(bytes).is_err());
+    /// ```
+    ///
+    #[doc = codegen_header!("h5", "try_mut_from_suffix")]
+    ///
+    /// See [`TryFromBytes::try_ref_from_suffix`](#method.try_ref_from_suffix.codegen).
+    #[must_use = "has no side effects"]
+    #[cfg_attr(zerocopy_inline_always, inline(always))]
+    #[cfg_attr(not(zerocopy_inline_always), inline)]
+    fn try_mut_from_suffix(
+        source: &mut [u8],
+    ) -> Result<(&mut [u8], &mut Self), TryCastError<&mut [u8], Self>>
+    where
+        Self: KnownLayout + IntoBytes,
+    {
+        static_assert_dst_is_not_zst!(Self);
+        try_mut_from_prefix_suffix(source, CastType::Suffix, None).map(swap)
+    }
+
+    /// Attempts to interpret the given `source` as a `&Self` with a DST length
+    /// equal to `count`.
+    ///
+    /// This method attempts to return a reference to `source` interpreted as a
+    /// `Self` with `count` trailing elements. If the length of `source` is not
+    /// equal to the size of `Self` with `count` elements, if `source` is not
+    /// appropriately aligned, or if `source` does not contain a valid instance
+    /// of `Self`, this returns `Err`. If [`Self: Unaligned`][self-unaligned],
+    /// you can [infallibly discard the alignment error][ConvertError::from].
+    ///
+    /// [self-unaligned]: Unaligned
+    /// [slice-dst]: KnownLayout#dynamically-sized-types
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # #![allow(non_camel_case_types)] // For C0::xC0
+    /// use zerocopy::TryFromBytes;
+    /// # use zerocopy_derive::*;
+    ///
+    /// // The only valid value of this type is the byte `0xC0`
+    /// #[derive(TryFromBytes, KnownLayout, Immutable)]
+    /// #[repr(u8)]
+    /// enum C0 { xC0 = 0xC0 }
+    ///
+    /// // The only valid value of this type is the bytes `0xC0C0`.
+    /// #[derive(TryFromBytes, KnownLayout, Immutable)]
+    /// #[repr(C)]
+    /// struct C0C0(C0, C0);
+    ///
+    /// #[derive(TryFromBytes, KnownLayout, Immutable)]
+    /// #[repr(C)]
+    /// struct Packet {
+    ///     magic_number: C0C0,
+    ///     mug_size: u8,
+    ///     temperature: u8,
+    ///     marshmallows: [[u8; 2]],
+    /// }
+    ///
+    /// let bytes = &[0xC0, 0xC0, 240, 77, 2, 3, 4, 5, 6, 7][..];
+    ///
+    /// let packet = Packet::try_ref_from_bytes_with_elems(bytes, 3).unwrap();
+    ///
+    /// assert_eq!(packet.mug_size, 240);
+    /// assert_eq!(packet.temperature, 77);
+    /// assert_eq!(packet.marshmallows, [[2, 3], [4, 5], [6, 7]]);
+    ///
+    /// // These bytes are not valid instance of `Packet`.
+    /// let bytes = &[0, 1, 2, 3, 4, 5, 6, 77, 240, 0xC0, 0xC0][..];
+    /// assert!(Packet::try_ref_from_bytes_with_elems(bytes, 3).is_err());
+    /// ```
+    ///
+    /// Since an explicit `count` is provided, this method supports types with
+    /// zero-sized trailing slice elements. Methods such as [`try_ref_from_bytes`]
+    /// which do not take an explicit count do not support such types.
+    ///
+    /// ```
+    /// use core::num::NonZeroU16;
+    /// use zerocopy::*;
+    /// # use zerocopy_derive::*;
+    ///
+    /// #[derive(TryFromBytes, Immutable, KnownLayout)]
+    /// #[repr(C)]
+    /// struct ZSTy {
+    ///     leading_sized: NonZeroU16,
+    ///     trailing_dst: [()],
+    /// }
+    ///
+    /// let src = 0xCAFEu16.as_bytes();
+    /// let zsty = ZSTy::try_ref_from_bytes_with_elems(src, 42).unwrap();
+    /// assert_eq!(zsty.trailing_dst.len(), 42);
+    /// ```
+    ///
+    /// [`try_ref_from_bytes`]: TryFromBytes::try_ref_from_bytes
+    ///
+    #[doc = codegen_section!(
+        header = "h5",
+        bench = "try_ref_from_bytes_with_elems",
+        format = "coco",
+        arity = 2,
+        [
+            open
+            @index 1
+            @title "Unsized"
+            @variant "dynamic_size"
+        ],
+        [
+            @index 2
+            @title "Dynamically Padded"
+            @variant "dynamic_padding"
+        ]
+    )]
+    #[must_use = "has no side effects"]
+    #[cfg_attr(zerocopy_inline_always, inline(always))]
+    #[cfg_attr(not(zerocopy_inline_always), inline)]
+    fn try_ref_from_bytes_with_elems(
+        source: &[u8],
+        count: usize,
+    ) -> Result<&Self, TryCastError<&[u8], Self>>
+    where
+        Self: KnownLayout<PointerMetadata = usize> + Immutable,
+    {
+        match Ptr::from_ref(source).try_cast_into_no_leftover::<Self, BecauseImmutable>(Some(count))
+        {
+            Ok(source) => {
+                // This call may panic. If that happens, it doesn't cause any soundness
+                // issues, as we have not generated any invalid state which we need to
+                // fix before returning.
+                match source.try_into_valid() {
+                    Ok(source) => Ok(source.as_ref()),
+                    Err(e) => {
+                        Err(e.map_src(|src| src.as_bytes::<BecauseImmutable>().as_ref()).into())
+                    }
+                }
+            }
+            Err(e) => Err(e.map_src(Ptr::as_ref).into()),
+        }
+    }
+
+    /// Attempts to interpret the prefix of the given `source` as a `&Self` with
+    /// a DST length equal to `count`.
+    ///
+    /// This method attempts to return a reference to the prefix of `source`
+    /// interpreted as a `Self` with `count` trailing elements, and a reference
+    /// to the remaining bytes. If the length of `source` is less than the size
+    /// of `Self` with `count` elements, if `source` is not appropriately
+    /// aligned, or if the prefix of `source` does not contain a valid instance
+    /// of `Self`, this returns `Err`. If [`Self: Unaligned`][self-unaligned],
+    /// you can [infallibly discard the alignment error][ConvertError::from].
+    ///
+    /// [self-unaligned]: Unaligned
+    /// [slice-dst]: KnownLayout#dynamically-sized-types
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # #![allow(non_camel_case_types)] // For C0::xC0
+    /// use zerocopy::TryFromBytes;
+    /// # use zerocopy_derive::*;
+    ///
+    /// // The only valid value of this type is the byte `0xC0`
+    /// #[derive(TryFromBytes, KnownLayout, Immutable)]
+    /// #[repr(u8)]
+    /// enum C0 { xC0 = 0xC0 }
+    ///
+    /// // The only valid value of this type is the bytes `0xC0C0`.
+    /// #[derive(TryFromBytes, KnownLayout, Immutable)]
+    /// #[repr(C)]
+    /// struct C0C0(C0, C0);
+    ///
+    /// #[derive(TryFromBytes, KnownLayout, Immutable)]
+    /// #[repr(C)]
+    /// struct Packet {
+    ///     magic_number: C0C0,
+    ///     mug_size: u8,
+    ///     temperature: u8,
+    ///     marshmallows: [[u8; 2]],
+    /// }
+    ///
+    /// let bytes = &[0xC0, 0xC0, 240, 77, 2, 3, 4, 5, 6, 7, 8][..];
+    ///
+    /// let (packet, suffix) = Packet::try_ref_from_prefix_with_elems(bytes, 3).unwrap();
+    ///
+    /// assert_eq!(packet.mug_size, 240);
+    /// assert_eq!(packet.temperature, 77);
+    /// assert_eq!(packet.marshmallows, [[2, 3], [4, 5], [6, 7]]);
+    /// assert_eq!(suffix, &[8u8][..]);
+    ///
+    /// // These bytes are not valid instance of `Packet`.
+    /// let bytes = &mut [0, 1, 2, 3, 4, 5, 6, 7, 8, 77, 240, 0xC0, 0xC0][..];
+    /// assert!(Packet::try_ref_from_prefix_with_elems(bytes, 3).is_err());
+    /// ```
+    ///
+    /// Since an explicit `count` is provided, this method supports types with
+    /// zero-sized trailing slice elements. Methods such as [`try_ref_from_prefix`]
+    /// which do not take an explicit count do not support such types.
+    ///
+    /// ```
+    /// use core::num::NonZeroU16;
+    /// use zerocopy::*;
+    /// # use zerocopy_derive::*;
+    ///
+    /// #[derive(TryFromBytes, Immutable, KnownLayout)]
+    /// #[repr(C)]
+    /// struct ZSTy {
+    ///     leading_sized: NonZeroU16,
+    ///     trailing_dst: [()],
+    /// }
+    ///
+    /// let src = 0xCAFEu16.as_bytes();
+    /// let (zsty, _) = ZSTy::try_ref_from_prefix_with_elems(src, 42).unwrap();
+    /// assert_eq!(zsty.trailing_dst.len(), 42);
+    /// ```
+    ///
+    /// [`try_ref_from_prefix`]: TryFromBytes::try_ref_from_prefix
+    ///
+    #[doc = codegen_section!(
+        header = "h5",
+        bench = "try_ref_from_prefix_with_elems",
+        format = "coco",
+        arity = 2,
+        [
+            open
+            @index 1
+            @title "Unsized"
+            @variant "dynamic_size"
+        ],
+        [
+            @index 2
+            @title "Dynamically Padded"
+            @variant "dynamic_padding"
+        ]
+    )]
+    #[must_use = "has no side effects"]
+    #[cfg_attr(zerocopy_inline_always, inline(always))]
+    #[cfg_attr(not(zerocopy_inline_always), inline)]
+    fn try_ref_from_prefix_with_elems(
+        source: &[u8],
+        count: usize,
+    ) -> Result<(&Self, &[u8]), TryCastError<&[u8], Self>>
+    where
+        Self: KnownLayout<PointerMetadata = usize> + Immutable,
+    {
+        try_ref_from_prefix_suffix(source, CastType::Prefix, Some(count))
+    }
+
+    /// Attempts to interpret the suffix of the given `source` as a `&Self` with
+    /// a DST length equal to `count`.
+    ///
+    /// This method attempts to return a reference to the suffix of `source`
+    /// interpreted as a `Self` with `count` trailing elements, and a reference
+    /// to the preceding bytes. If the length of `source` is less than the size
+    /// of `Self` with `count` elements, if the suffix of `source` is not
+    /// appropriately aligned, or if the suffix of `source` does not contain a
+    /// valid instance of `Self`, this returns `Err`. If [`Self:
+    /// Unaligned`][self-unaligned], you can [infallibly discard the alignment
+    /// error][ConvertError::from].
+    ///
+    /// [self-unaligned]: Unaligned
+    /// [slice-dst]: KnownLayout#dynamically-sized-types
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # #![allow(non_camel_case_types)] // For C0::xC0
+    /// use zerocopy::TryFromBytes;
+    /// # use zerocopy_derive::*;
+    ///
+    /// // The only valid value of this type is the byte `0xC0`
+    /// #[derive(TryFromBytes, KnownLayout, Immutable)]
+    /// #[repr(u8)]
+    /// enum C0 { xC0 = 0xC0 }
+    ///
+    /// // The only valid value of this type is the bytes `0xC0C0`.
+    /// #[derive(TryFromBytes, KnownLayout, Immutable)]
+    /// #[repr(C)]
+    /// struct C0C0(C0, C0);
+    ///
+    /// #[derive(TryFromBytes, KnownLayout, Immutable)]
+    /// #[repr(C)]
+    /// struct Packet {
+    ///     magic_number: C0C0,
+    ///     mug_size: u8,
+    ///     temperature: u8,
+    ///     marshmallows: [[u8; 2]],
+    /// }
+    ///
+    /// let bytes = &[123, 0xC0, 0xC0, 240, 77, 2, 3, 4, 5, 6, 7][..];
+    ///
+    /// let (prefix, packet) = Packet::try_ref_from_suffix_with_elems(bytes, 3).unwrap();
+    ///
+    /// assert_eq!(packet.mug_size, 240);
+    /// assert_eq!(packet.temperature, 77);
+    /// assert_eq!(packet.marshmallows, [[2, 3], [4, 5], [6, 7]]);
+    /// assert_eq!(prefix, &[123u8][..]);
+    ///
+    /// // These bytes are not valid instance of `Packet`.
+    /// let bytes = &[0, 1, 2, 3, 4, 5, 6, 7, 8, 77, 240, 0xC0, 0xC0][..];
+    /// assert!(Packet::try_ref_from_suffix_with_elems(bytes, 3).is_err());
+    /// ```
+    ///
+    /// Since an explicit `count` is provided, this method supports types with
+    /// zero-sized trailing slice elements. Methods such as [`try_ref_from_prefix`]
+    /// which do not take an explicit count do not support such types.
+    ///
+    /// ```
+    /// use core::num::NonZeroU16;
+    /// use zerocopy::*;
+    /// # use zerocopy_derive::*;
+    ///
+    /// #[derive(TryFromBytes, Immutable, KnownLayout)]
+    /// #[repr(C)]
+    /// struct ZSTy {
+    ///     leading_sized: NonZeroU16,
+    ///     trailing_dst: [()],
+    /// }
+    ///
+    /// let src = 0xCAFEu16.as_bytes();
+    /// let (_, zsty) = ZSTy::try_ref_from_suffix_with_elems(src, 42).unwrap();
+    /// assert_eq!(zsty.trailing_dst.len(), 42);
+    /// ```
+    ///
+    /// [`try_ref_from_prefix`]: TryFromBytes::try_ref_from_prefix
+    ///
+    #[doc = codegen_section!(
+        header = "h5",
+        bench = "try_ref_from_suffix_with_elems",
+        format = "coco",
+        arity = 2,
+        [
+            open
+            @index 1
+            @title "Unsized"
+            @variant "dynamic_size"
+        ],
+        [
+            @index 2
+            @title "Dynamically Padded"
+            @variant "dynamic_padding"
+        ]
+    )]
+    #[must_use = "has no side effects"]
+    #[cfg_attr(zerocopy_inline_always, inline(always))]
+    #[cfg_attr(not(zerocopy_inline_always), inline)]
+    fn try_ref_from_suffix_with_elems(
+        source: &[u8],
+        count: usize,
+    ) -> Result<(&[u8], &Self), TryCastError<&[u8], Self>>
+    where
+        Self: KnownLayout<PointerMetadata = usize> + Immutable,
+    {
+        try_ref_from_prefix_suffix(source, CastType::Suffix, Some(count)).map(swap)
+    }
+
+    /// Attempts to interpret the given `source` as a `&mut Self` with a DST
+    /// length equal to `count`.
+    ///
+    /// This method attempts to return a reference to `source` interpreted as a
+    /// `Self` with `count` trailing elements. If the length of `source` is not
+    /// equal to the size of `Self` with `count` elements, if `source` is not
+    /// appropriately aligned, or if `source` does not contain a valid instance
+    /// of `Self`, this returns `Err`. If [`Self: Unaligned`][self-unaligned],
+    /// you can [infallibly discard the alignment error][ConvertError::from].
+    ///
+    /// [self-unaligned]: Unaligned
+    /// [slice-dst]: KnownLayout#dynamically-sized-types
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # #![allow(non_camel_case_types)] // For C0::xC0
+    /// use zerocopy::TryFromBytes;
+    /// # use zerocopy_derive::*;
+    ///
+    /// // The only valid value of this type is the byte `0xC0`
+    /// #[derive(TryFromBytes, IntoBytes, KnownLayout)]
+    /// #[repr(u8)]
+    /// enum C0 { xC0 = 0xC0 }
+    ///
+    /// // The only valid value of this type is the bytes `0xC0C0`.
+    /// #[derive(TryFromBytes, IntoBytes, KnownLayout)]
+    /// #[repr(C)]
+    /// struct C0C0(C0, C0);
+    ///
+    /// #[derive(TryFromBytes, IntoBytes, KnownLayout)]
+    /// #[repr(C, packed)]
+    /// struct Packet {
+    ///     magic_number: C0C0,
+    ///     mug_size: u8,
+    ///     temperature: u8,
+    ///     marshmallows: [[u8; 2]],
+    /// }
+    ///
+    /// let bytes = &mut [0xC0, 0xC0, 240, 77, 2, 3, 4, 5, 6, 7][..];
+    ///
+    /// let packet = Packet::try_mut_from_bytes_with_elems(bytes, 3).unwrap();
+    ///
+    /// assert_eq!(packet.mug_size, 240);
+    /// assert_eq!(packet.temperature, 77);
+    /// assert_eq!(packet.marshmallows, [[2, 3], [4, 5], [6, 7]]);
+    ///
+    /// packet.temperature = 111;
+    ///
+    /// assert_eq!(bytes, [0xC0, 0xC0, 240, 111, 2, 3, 4, 5, 6, 7]);
+    ///
+    /// // These bytes are not valid instance of `Packet`.
+    /// let bytes = &mut [0, 1, 2, 3, 4, 5, 6, 77, 240, 0xC0, 0xC0][..];
+    /// assert!(Packet::try_mut_from_bytes_with_elems(bytes, 3).is_err());
+    /// ```
+    ///
+    /// Since an explicit `count` is provided, this method supports types with
+    /// zero-sized trailing slice elements. Methods such as [`try_mut_from_bytes`]
+    /// which do not take an explicit count do not support such types.
+    ///
+    /// ```
+    /// use core::num::NonZeroU16;
+    /// use zerocopy::*;
+    /// # use zerocopy_derive::*;
+    ///
+    /// #[derive(TryFromBytes, IntoBytes, KnownLayout)]
+    /// #[repr(C, packed)]
+    /// struct ZSTy {
+    ///     leading_sized: NonZeroU16,
+    ///     trailing_dst: [()],
+    /// }
+    ///
+    /// let mut src = 0xCAFEu16;
+    /// let src = src.as_mut_bytes();
+    /// let zsty = ZSTy::try_mut_from_bytes_with_elems(src, 42).unwrap();
+    /// assert_eq!(zsty.trailing_dst.len(), 42);
+    /// ```
+    ///
+    /// [`try_mut_from_bytes`]: TryFromBytes::try_mut_from_bytes
+    ///  
+    #[doc = codegen_header!("h5", "try_mut_from_bytes_with_elems")]
+    ///
+    /// See [`TryFromBytes::try_ref_from_bytes_with_elems`](#method.try_ref_from_bytes_with_elems.codegen).
+    #[must_use = "has no side effects"]
+    #[cfg_attr(zerocopy_inline_always, inline(always))]
+    #[cfg_attr(not(zerocopy_inline_always), inline)]
+    fn try_mut_from_bytes_with_elems(
+        source: &mut [u8],
+        count: usize,
+    ) -> Result<&mut Self, TryCastError<&mut [u8], Self>>
+    where
+        Self: KnownLayout<PointerMetadata = usize> + IntoBytes,
+    {
+        match Ptr::from_mut(source).try_cast_into_no_leftover::<Self, BecauseExclusive>(Some(count))
+        {
+            Ok(source) => {
+                // This call may panic. If that happens, it doesn't cause any soundness
+                // issues, as we have not generated any invalid state which we need to
+                // fix before returning.
+                match source.try_into_valid() {
+                    Ok(source) => Ok(source.as_mut()),
+                    Err(e) => Err(e.map_src(|src| src.as_bytes().as_mut()).into()),
+                }
+            }
+            Err(e) => Err(e.map_src(Ptr::as_mut).into()),
+        }
+    }
+
+    /// Attempts to interpret the prefix of the given `source` as a `&mut Self`
+    /// with a DST length equal to `count`.
+    ///
+    /// This method attempts to return a reference to the prefix of `source`
+    /// interpreted as a `Self` with `count` trailing elements, and a reference
+    /// to the remaining bytes. If the length of `source` is less than the size
+    /// of `Self` with `count` elements, if `source` is not appropriately
+    /// aligned, or if the prefix of `source` does not contain a valid instance
+    /// of `Self`, this returns `Err`. If [`Self: Unaligned`][self-unaligned],
+    /// you can [infallibly discard the alignment error][ConvertError::from].
+    ///
+    /// [self-unaligned]: Unaligned
+    /// [slice-dst]: KnownLayout#dynamically-sized-types
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # #![allow(non_camel_case_types)] // For C0::xC0
+    /// use zerocopy::TryFromBytes;
+    /// # use zerocopy_derive::*;
+    ///
+    /// // The only valid value of this type is the byte `0xC0`
+    /// #[derive(TryFromBytes, IntoBytes, KnownLayout)]
+    /// #[repr(u8)]
+    /// enum C0 { xC0 = 0xC0 }
+    ///
+    /// // The only valid value of this type is the bytes `0xC0C0`.
+    /// #[derive(TryFromBytes, IntoBytes, KnownLayout)]
+    /// #[repr(C)]
+    /// struct C0C0(C0, C0);
+    ///
+    /// #[derive(TryFromBytes, IntoBytes, KnownLayout)]
+    /// #[repr(C, packed)]
+    /// struct Packet {
+    ///     magic_number: C0C0,
+    ///     mug_size: u8,
+    ///     temperature: u8,
+    ///     marshmallows: [[u8; 2]],
+    /// }
+    ///
+    /// let bytes = &mut [0xC0, 0xC0, 240, 77, 2, 3, 4, 5, 6, 7, 8][..];
+    ///
+    /// let (packet, suffix) = Packet::try_mut_from_prefix_with_elems(bytes, 3).unwrap();
+    ///
+    /// assert_eq!(packet.mug_size, 240);
+    /// assert_eq!(packet.temperature, 77);
+    /// assert_eq!(packet.marshmallows, [[2, 3], [4, 5], [6, 7]]);
+    /// assert_eq!(suffix, &[8u8][..]);
+    ///
+    /// packet.temperature = 111;
+    /// suffix[0] = 222;
+    ///
+    /// assert_eq!(bytes, [0xC0, 0xC0, 240, 111, 2, 3, 4, 5, 6, 7, 222]);
+    ///
+    /// // These bytes are not valid instance of `Packet`.
+    /// let bytes = &mut [0, 1, 2, 3, 4, 5, 6, 7, 8, 77, 240, 0xC0, 0xC0][..];
+    /// assert!(Packet::try_mut_from_prefix_with_elems(bytes, 3).is_err());
+    /// ```
+    ///
+    /// Since an explicit `count` is provided, this method supports types with
+    /// zero-sized trailing slice elements. Methods such as [`try_mut_from_prefix`]
+    /// which do not take an explicit count do not support such types.
+    ///
+    /// ```
+    /// use core::num::NonZeroU16;
+    /// use zerocopy::*;
+    /// # use zerocopy_derive::*;
+    ///
+    /// #[derive(TryFromBytes, IntoBytes, KnownLayout)]
+    /// #[repr(C, packed)]
+    /// struct ZSTy {
+    ///     leading_sized: NonZeroU16,
+    ///     trailing_dst: [()],
+    /// }
+    ///
+    /// let mut src = 0xCAFEu16;
+    /// let src = src.as_mut_bytes();
+    /// let (zsty, _) = ZSTy::try_mut_from_prefix_with_elems(src, 42).unwrap();
+    /// assert_eq!(zsty.trailing_dst.len(), 42);
+    /// ```
+    ///
+    /// [`try_mut_from_prefix`]: TryFromBytes::try_mut_from_prefix
+    ///
+    #[doc = codegen_header!("h5", "try_mut_from_prefix_with_elems")]
+    ///
+    /// See [`TryFromBytes::try_ref_from_prefix_with_elems`](#method.try_ref_from_prefix_with_elems.codegen).
+    #[must_use = "has no side effects"]
+    #[cfg_attr(zerocopy_inline_always, inline(always))]
+    #[cfg_attr(not(zerocopy_inline_always), inline)]
+    fn try_mut_from_prefix_with_elems(
+        source: &mut [u8],
+        count: usize,
+    ) -> Result<(&mut Self, &mut [u8]), TryCastError<&mut [u8], Self>>
+    where
+        Self: KnownLayout<PointerMetadata = usize> + IntoBytes,
+    {
+        try_mut_from_prefix_suffix(source, CastType::Prefix, Some(count))
+    }
+
+    /// Attempts to interpret the suffix of the given `source` as a `&mut Self`
+    /// with a DST length equal to `count`.
+    ///
+    /// This method attempts to return a reference to the suffix of `source`
+    /// interpreted as a `Self` with `count` trailing elements, and a reference
+    /// to the preceding bytes. If the length of `source` is less than the size
+    /// of `Self` with `count` elements, if the suffix of `source` is not
+    /// appropriately aligned, or if the suffix of `source` does not contain a
+    /// valid instance of `Self`, this returns `Err`. If [`Self:
+    /// Unaligned`][self-unaligned], you can [infallibly discard the alignment
+    /// error][ConvertError::from].
+    ///
+    /// [self-unaligned]: Unaligned
+    /// [slice-dst]: KnownLayout#dynamically-sized-types
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # #![allow(non_camel_case_types)] // For C0::xC0
+    /// use zerocopy::TryFromBytes;
+    /// # use zerocopy_derive::*;
+    ///
+    /// // The only valid value of this type is the byte `0xC0`
+    /// #[derive(TryFromBytes, IntoBytes, KnownLayout)]
+    /// #[repr(u8)]
+    /// enum C0 { xC0 = 0xC0 }
+    ///
+    /// // The only valid value of this type is the bytes `0xC0C0`.
+    /// #[derive(TryFromBytes, IntoBytes, KnownLayout)]
+    /// #[repr(C)]
+    /// struct C0C0(C0, C0);
+    ///
+    /// #[derive(TryFromBytes, IntoBytes, KnownLayout)]
+    /// #[repr(C, packed)]
+    /// struct Packet {
+    ///     magic_number: C0C0,
+    ///     mug_size: u8,
+    ///     temperature: u8,
+    ///     marshmallows: [[u8; 2]],
+    /// }
+    ///
+    /// let bytes = &mut [123, 0xC0, 0xC0, 240, 77, 2, 3, 4, 5, 6, 7][..];
+    ///
+    /// let (prefix, packet) = Packet::try_mut_from_suffix_with_elems(bytes, 3).unwrap();
+    ///
+    /// assert_eq!(packet.mug_size, 240);
+    /// assert_eq!(packet.temperature, 77);
+    /// assert_eq!(packet.marshmallows, [[2, 3], [4, 5], [6, 7]]);
+    /// assert_eq!(prefix, &[123u8][..]);
+    ///
+    /// prefix[0] = 111;
+    /// packet.temperature = 222;
+    ///
+    /// assert_eq!(bytes, [111, 0xC0, 0xC0, 240, 222, 2, 3, 4, 5, 6, 7]);
+    ///
+    /// // These bytes are not valid instance of `Packet`.
+    /// let bytes = &mut [0, 1, 2, 3, 4, 5, 6, 7, 8, 77, 240, 0xC0, 0xC0][..];
+    /// assert!(Packet::try_mut_from_suffix_with_elems(bytes, 3).is_err());
+    /// ```
+    ///
+    /// Since an explicit `count` is provided, this method supports types with
+    /// zero-sized trailing slice elements. Methods such as [`try_mut_from_prefix`]
+    /// which do not take an explicit count do not support such types.
+    ///
+    /// ```
+    /// use core::num::NonZeroU16;
+    /// use zerocopy::*;
+    /// # use zerocopy_derive::*;
+    ///
+    /// #[derive(TryFromBytes, IntoBytes, KnownLayout)]
+    /// #[repr(C, packed)]
+    /// struct ZSTy {
+    ///     leading_sized: NonZeroU16,
+    ///     trailing_dst: [()],
+    /// }
+    ///
+    /// let mut src = 0xCAFEu16;
+    /// let src = src.as_mut_bytes();
+    /// let (_, zsty) = ZSTy::try_mut_from_suffix_with_elems(src, 42).unwrap();
+    /// assert_eq!(zsty.trailing_dst.len(), 42);
+    /// ```
+    ///
+    /// [`try_mut_from_prefix`]: TryFromBytes::try_mut_from_prefix
+    ///
+    #[doc = codegen_header!("h5", "try_mut_from_suffix_with_elems")]
+    ///
+    /// See [`TryFromBytes::try_ref_from_suffix_with_elems`](#method.try_ref_from_suffix_with_elems.codegen).
+    #[must_use = "has no side effects"]
+    #[cfg_attr(zerocopy_inline_always, inline(always))]
+    #[cfg_attr(not(zerocopy_inline_always), inline)]
+    fn try_mut_from_suffix_with_elems(
+        source: &mut [u8],
+        count: usize,
+    ) -> Result<(&mut [u8], &mut Self), TryCastError<&mut [u8], Self>>
+    where
+        Self: KnownLayout<PointerMetadata = usize> + IntoBytes,
+    {
+        try_mut_from_prefix_suffix(source, CastType::Suffix, Some(count)).map(swap)
+    }
+
+    /// Attempts to read the given `source` as a `Self`.
+    ///
+    /// If `source.len() != size_of::<Self>()` or the bytes are not a valid
+    /// instance of `Self`, this returns `Err`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use zerocopy::TryFromBytes;
+    /// # use zerocopy_derive::*;
+    ///
+    /// // The only valid value of this type is the byte `0xC0`
+    /// #[derive(TryFromBytes)]
+    /// #[repr(u8)]
+    /// enum C0 { xC0 = 0xC0 }
+    ///
+    /// // The only valid value of this type is the bytes `0xC0C0`.
+    /// #[derive(TryFromBytes)]
+    /// #[repr(C)]
+    /// struct C0C0(C0, C0);
+    ///
+    /// #[derive(TryFromBytes)]
+    /// #[repr(C)]
+    /// struct Packet {
+    ///     magic_number: C0C0,
+    ///     mug_size: u8,
+    ///     temperature: u8,
+    /// }
+    ///
+    /// let bytes = &[0xC0, 0xC0, 240, 77][..];
+    ///
+    /// let packet = Packet::try_read_from_bytes(bytes).unwrap();
+    ///
+    /// assert_eq!(packet.mug_size, 240);
+    /// assert_eq!(packet.temperature, 77);
+    ///
+    /// // These bytes are not valid instance of `Packet`.
+    /// let bytes = &mut [0x10, 0xC0, 240, 77][..];
+    /// assert!(Packet::try_read_from_bytes(bytes).is_err());
+    /// ```
+    ///
+    /// # Performance Considerations
+    ///
+    /// In this version of zerocopy, this method reads the `source` into a
+    /// well-aligned stack allocation and *then* validates that the allocation
+    /// is a valid `Self`. This ensures that validation can be performed using
+    /// aligned reads (which carry a performance advantage over unaligned reads
+    /// on many platforms) at the cost of an unconditional copy.
+    ///
+    #[doc = codegen_section!(
+        header = "h5",
+        bench = "try_read_from_bytes",
+        format = "coco_static_size",
+    )]
+    #[must_use = "has no side effects"]
+    #[cfg_attr(zerocopy_inline_always, inline(always))]
+    #[cfg_attr(not(zerocopy_inline_always), inline)]
+    fn try_read_from_bytes(source: &[u8]) -> Result<Self, TryReadError<&[u8], Self>>
+    where
+        Self: Sized,
+    {
+        // FIXME(#2981): If `align_of::<Self>() == 1`, validate `source` in-place.
+
+        let candidate = match CoreMaybeUninit::<Self>::read_from_bytes(source) {
+            Ok(candidate) => candidate,
+            Err(e) => {
+                return Err(TryReadError::Size(e.with_dst()));
+            }
+        };
+        // SAFETY: `candidate` was copied from from `source: &[u8]`, so all of
+        // its bytes are initialized.
+        unsafe { try_read_from(source, candidate) }
+    }
+
+    /// Attempts to read a `Self` from the prefix of the given `source`.
+    ///
+    /// This attempts to read a `Self` from the first `size_of::<Self>()` bytes
+    /// of `source`, returning that `Self` and any remaining bytes. If
+    /// `source.len() < size_of::<Self>()` or the bytes are not a valid instance
+    /// of `Self`, it returns `Err`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use zerocopy::TryFromBytes;
+    /// # use zerocopy_derive::*;
+    ///
+    /// // The only valid value of this type is the byte `0xC0`
+    /// #[derive(TryFromBytes)]
+    /// #[repr(u8)]
+    /// enum C0 { xC0 = 0xC0 }
+    ///
+    /// // The only valid value of this type is the bytes `0xC0C0`.
+    /// #[derive(TryFromBytes)]
+    /// #[repr(C)]
+    /// struct C0C0(C0, C0);
+    ///
+    /// #[derive(TryFromBytes)]
+    /// #[repr(C)]
+    /// struct Packet {
+    ///     magic_number: C0C0,
+    ///     mug_size: u8,
+    ///     temperature: u8,
+    /// }
+    ///
+    /// // These are more bytes than are needed to encode a `Packet`.
+    /// let bytes = &[0xC0, 0xC0, 240, 77, 0, 1, 2, 3, 4, 5, 6][..];
+    ///
+    /// let (packet, suffix) = Packet::try_read_from_prefix(bytes).unwrap();
+    ///
+    /// assert_eq!(packet.mug_size, 240);
+    /// assert_eq!(packet.temperature, 77);
+    /// assert_eq!(suffix, &[0u8, 1, 2, 3, 4, 5, 6][..]);
+    ///
+    /// // These bytes are not valid instance of `Packet`.
+    /// let bytes = &[0x10, 0xC0, 240, 77, 0, 1, 2, 3, 4, 5, 6][..];
+    /// assert!(Packet::try_read_from_prefix(bytes).is_err());
+    /// ```
+    ///
+    /// # Performance Considerations
+    ///
+    /// In this version of zerocopy, this method reads the `source` into a
+    /// well-aligned stack allocation and *then* validates that the allocation
+    /// is a valid `Self`. This ensures that validation can be performed using
+    /// aligned reads (which carry a performance advantage over unaligned reads
+    /// on many platforms) at the cost of an unconditional copy.
+    ///
+    #[doc = codegen_section!(
+        header = "h5",
+        bench = "try_read_from_prefix",
+        format = "coco_static_size",
+    )]
+    #[must_use = "has no side effects"]
+    #[cfg_attr(zerocopy_inline_always, inline(always))]
+    #[cfg_attr(not(zerocopy_inline_always), inline)]
+    fn try_read_from_prefix(source: &[u8]) -> Result<(Self, &[u8]), TryReadError<&[u8], Self>>
+    where
+        Self: Sized,
+    {
+        // FIXME(#2981): If `align_of::<Self>() == 1`, validate `source` in-place.
+
+        let (candidate, suffix) = match CoreMaybeUninit::<Self>::read_from_prefix(source) {
+            Ok(candidate) => candidate,
+            Err(e) => {
+                return Err(TryReadError::Size(e.with_dst()));
+            }
+        };
+        // SAFETY: `candidate` was copied from from `source: &[u8]`, so all of
+        // its bytes are initialized.
+        unsafe { try_read_from(source, candidate).map(|slf| (slf, suffix)) }
+    }
+
+    /// Attempts to read a `Self` from the suffix of the given `source`.
+    ///
+    /// This attempts to read a `Self` from the last `size_of::<Self>()` bytes
+    /// of `source`, returning that `Self` and any preceding bytes. If
+    /// `source.len() < size_of::<Self>()` or the bytes are not a valid instance
+    /// of `Self`, it returns `Err`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # #![allow(non_camel_case_types)] // For C0::xC0
+    /// use zerocopy::TryFromBytes;
+    /// # use zerocopy_derive::*;
+    ///
+    /// // The only valid value of this type is the byte `0xC0`
+    /// #[derive(TryFromBytes)]
+    /// #[repr(u8)]
+    /// enum C0 { xC0 = 0xC0 }
+    ///
+    /// // The only valid value of this type is the bytes `0xC0C0`.
+    /// #[derive(TryFromBytes)]
+    /// #[repr(C)]
+    /// struct C0C0(C0, C0);
+    ///
+    /// #[derive(TryFromBytes)]
+    /// #[repr(C)]
+    /// struct Packet {
+    ///     magic_number: C0C0,
+    ///     mug_size: u8,
+    ///     temperature: u8,
+    /// }
+    ///
+    /// // These are more bytes than are needed to encode a `Packet`.
+    /// let bytes = &[0, 1, 2, 3, 4, 5, 0xC0, 0xC0, 240, 77][..];
+    ///
+    /// let (prefix, packet) = Packet::try_read_from_suffix(bytes).unwrap();
+    ///
+    /// assert_eq!(packet.mug_size, 240);
+    /// assert_eq!(packet.temperature, 77);
+    /// assert_eq!(prefix, &[0u8, 1, 2, 3, 4, 5][..]);
+    ///
+    /// // These bytes are not valid instance of `Packet`.
+    /// let bytes = &[0, 1, 2, 3, 4, 5, 0x10, 0xC0, 240, 77][..];
+    /// assert!(Packet::try_read_from_suffix(bytes).is_err());
+    /// ```
+    ///
+    /// # Performance Considerations
+    ///
+    /// In this version of zerocopy, this method reads the `source` into a
+    /// well-aligned stack allocation and *then* validates that the allocation
+    /// is a valid `Self`. This ensures that validation can be performed using
+    /// aligned reads (which carry a performance advantage over unaligned reads
+    /// on many platforms) at the cost of an unconditional copy.
+    ///
+    #[doc = codegen_section!(
+        header = "h5",
+        bench = "try_read_from_suffix",
+        format = "coco_static_size",
+    )]
+    #[must_use = "has no side effects"]
+    #[cfg_attr(zerocopy_inline_always, inline(always))]
+    #[cfg_attr(not(zerocopy_inline_always), inline)]
+    fn try_read_from_suffix(source: &[u8]) -> Result<(&[u8], Self), TryReadError<&[u8], Self>>
+    where
+        Self: Sized,
+    {
+        // FIXME(#2981): If `align_of::<Self>() == 1`, validate `source` in-place.
+
+        let (prefix, candidate) = match CoreMaybeUninit::<Self>::read_from_suffix(source) {
+            Ok(candidate) => candidate,
+            Err(e) => {
+                return Err(TryReadError::Size(e.with_dst()));
+            }
+        };
+        // SAFETY: `candidate` was copied from from `source: &[u8]`, so all of
+        // its bytes are initialized.
+        unsafe { try_read_from(source, candidate).map(|slf| (prefix, slf)) }
+    }
+}
+
+#[inline(always)]
+fn try_ref_from_prefix_suffix<T: TryFromBytes + KnownLayout + Immutable + ?Sized>(
+    source: &[u8],
+    cast_type: CastType,
+    meta: Option<T::PointerMetadata>,
+) -> Result<(&T, &[u8]), TryCastError<&[u8], T>> {
+    match Ptr::from_ref(source).try_cast_into::<T, BecauseImmutable>(cast_type, meta) {
+        Ok((source, prefix_suffix)) => {
+            // This call may panic. If that happens, it doesn't cause any soundness
+            // issues, as we have not generated any invalid state which we need to
+            // fix before returning.
+            match source.try_into_valid() {
+                Ok(valid) => Ok((valid.as_ref(), prefix_suffix.as_ref())),
+                Err(e) => Err(e.map_src(|src| src.as_bytes::<BecauseImmutable>().as_ref()).into()),
+            }
+        }
+        Err(e) => Err(e.map_src(Ptr::as_ref).into()),
+    }
+}
+
+#[inline(always)]
+fn try_mut_from_prefix_suffix<T: IntoBytes + TryFromBytes + KnownLayout + ?Sized>(
+    candidate: &mut [u8],
+    cast_type: CastType,
+    meta: Option<T::PointerMetadata>,
+) -> Result<(&mut T, &mut [u8]), TryCastError<&mut [u8], T>> {
+    match Ptr::from_mut(candidate).try_cast_into::<T, BecauseExclusive>(cast_type, meta) {
+        Ok((candidate, prefix_suffix)) => {
+            // This call may panic. If that happens, it doesn't cause any soundness
+            // issues, as we have not generated any invalid state which we need to
+            // fix before returning.
+            match candidate.try_into_valid() {
+                Ok(valid) => Ok((valid.as_mut(), prefix_suffix.as_mut())),
+                Err(e) => Err(e.map_src(|src| src.as_bytes().as_mut()).into()),
+            }
+        }
+        Err(e) => Err(e.map_src(Ptr::as_mut).into()),
+    }
+}
+
+#[inline(always)]
+fn swap<T, U>((t, u): (T, U)) -> (U, T) {
+    (u, t)
+}
+
+/// # Safety
+///
+/// All bytes of `candidate` must be initialized.
+#[inline(always)]
+unsafe fn try_read_from<S, T: TryFromBytes>(
+    source: S,
+    mut candidate: CoreMaybeUninit<T>,
+) -> Result<T, TryReadError<S, T>> {
+    // We use `from_mut` despite not mutating via `c_ptr` so that we don't need
+    // to add a `T: Immutable` bound.
+    let c_ptr = Ptr::from_mut(&mut candidate);
+    // SAFETY: `c_ptr` has no uninitialized sub-ranges because it derived from
+    // `candidate`, which the caller promises is entirely initialized. Since
+    // `candidate` is a `MaybeUninit`, it has no validity requirements, and so
+    // no values written to an `Initialized` `c_ptr` can violate its validity.
+    // Since `c_ptr` has `Exclusive` aliasing, no mutations may happen except
+    // via `c_ptr` so long as it is live, so we don't need to worry about the
+    // fact that `c_ptr` may have more restricted validity than `candidate`.
+    let c_ptr = unsafe { c_ptr.assume_validity::<invariant::Initialized>() };
+    let mut c_ptr = c_ptr.cast::<_, crate::pointer::cast::CastSized, _>();
+
+    // Since we don't have `T: KnownLayout`, we hack around that by using
+    // `Wrapping<T>`, which implements `KnownLayout` even if `T` doesn't.
+    //
+    // This call may panic. If that happens, it doesn't cause any soundness
+    // issues, as we have not generated any invalid state which we need to fix
+    // before returning.
+    if !Wrapping::<T>::is_bit_valid(c_ptr.reborrow_shared().forget_aligned()) {
+        return Err(ValidityError::new(source).into());
+    }
+
+    fn _assert_same_size_and_validity<T>()
+    where
+        Wrapping<T>: pointer::TransmuteFrom<T, invariant::Valid, invariant::Valid>,
+        T: pointer::TransmuteFrom<Wrapping<T>, invariant::Valid, invariant::Valid>,
+    {
+    }
+
+    _assert_same_size_and_validity::<T>();
+
+    // SAFETY: We just validated that `candidate` contains a valid
+    // `Wrapping<T>`, which has the same size and bit validity as `T`, as
+    // guaranteed by the preceding type assertion.
+    Ok(unsafe { candidate.assume_init() })
+}
+
+/// Types for which a sequence of `0` bytes is a valid instance.
+///
+/// Any memory region of the appropriate length which is guaranteed to contain
+/// only zero bytes can be viewed as any `FromZeros` type with no runtime
+/// overhead. This is useful whenever memory is known to be in a zeroed state,
+/// such memory returned from some allocation routines.
+///
+/// # Warning: Padding bytes
+///
+/// Note that, when a value is moved or copied, only the non-padding bytes of
+/// that value are guaranteed to be preserved. It is unsound to assume that
+/// values written to padding bytes are preserved after a move or copy. For more
+/// details, see the [`FromBytes` docs][frombytes-warning-padding-bytes].
+///
+/// [frombytes-warning-padding-bytes]: FromBytes#warning-padding-bytes
+///
+/// # Implementation
+///
+/// **Do not implement this trait yourself!** Instead, use
+/// [`#[derive(FromZeros)]`][derive]; e.g.:
+///
+/// ```
+/// # use zerocopy_derive::{FromZeros, Immutable};
+/// #[derive(FromZeros)]
+/// struct MyStruct {
+/// # /*
+///     ...
+/// # */
+/// }
+///
+/// #[derive(FromZeros)]
+/// #[repr(u8)]
+/// enum MyEnum {
+/// #   Variant0,
+/// # /*
+///     ...
+/// # */
+/// }
+///
+/// #[derive(FromZeros, Immutable)]
+/// union MyUnion {
+/// #   variant: u8,
+/// # /*
+///     ...
+/// # */
+/// }
+/// ```
+///
+/// This derive performs a sophisticated, compile-time safety analysis to
+/// determine whether a type is `FromZeros`.
+///
+/// # Safety
+///
+/// *This section describes what is required in order for `T: FromZeros`, and
+/// what unsafe code may assume of such types. If you don't plan on implementing
+/// `FromZeros` manually, and you don't plan on writing unsafe code that
+/// operates on `FromZeros` types, then you don't need to read this section.*
+///
+/// If `T: FromZeros`, then unsafe code may assume that it is sound to produce a
+/// `T` whose bytes are all initialized to zero. If a type is marked as
+/// `FromZeros` which violates this contract, it may cause undefined behavior.
+///
+/// `#[derive(FromZeros)]` only permits [types which satisfy these
+/// requirements][derive-analysis].
+///
+#[cfg_attr(
+    feature = "derive",
+    doc = "[derive]: zerocopy_derive::FromZeros",
+    doc = "[derive-analysis]: zerocopy_derive::FromZeros#analysis"
+)]
+#[cfg_attr(
+    not(feature = "derive"),
+    doc = concat!("[derive]: https://docs.rs/zerocopy/", env!("CARGO_PKG_VERSION"), "/zerocopy/derive.FromZeros.html"),
+    doc = concat!("[derive-analysis]: https://docs.rs/zerocopy/", env!("CARGO_PKG_VERSION"), "/zerocopy/derive.FromZeros.html#analysis"),
+)]
+#[cfg_attr(
+    not(no_zerocopy_diagnostic_on_unimplemented_1_78_0),
+    diagnostic::on_unimplemented(note = "Consider adding `#[derive(FromZeros)]` to `{Self}`")
+)]
+pub unsafe trait FromZeros: TryFromBytes {
+    // The `Self: Sized` bound makes it so that `FromZeros` is still object
+    // safe.
+    #[doc(hidden)]
+    fn only_derive_is_allowed_to_implement_this_trait()
+    where
+        Self: Sized;
+
+    /// Overwrites `self` with zeros.
+    ///
+    /// Sets every byte in `self` to 0. While this is similar to doing `*self =
+    /// Self::new_zeroed()`, it differs in that `zero` does not semantically
+    /// drop the current value and replace it with a new one — it simply
+    /// modifies the bytes of the existing value.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # use zerocopy::FromZeros;
+    /// # use zerocopy_derive::*;
+    /// #
+    /// #[derive(FromZeros)]
+    /// #[repr(C)]
+    /// struct PacketHeader {
+    ///     src_port: [u8; 2],
+    ///     dst_port: [u8; 2],
+    ///     length: [u8; 2],
+    ///     checksum: [u8; 2],
+    /// }
+    ///
+    /// let mut header = PacketHeader {
+    ///     src_port: 100u16.to_be_bytes(),
+    ///     dst_port: 200u16.to_be_bytes(),
+    ///     length: 300u16.to_be_bytes(),
+    ///     checksum: 400u16.to_be_bytes(),
+    /// };
+    ///
+    /// header.zero();
+    ///
+    /// assert_eq!(header.src_port, [0, 0]);
+    /// assert_eq!(header.dst_port, [0, 0]);
+    /// assert_eq!(header.length, [0, 0]);
+    /// assert_eq!(header.checksum, [0, 0]);
+    /// ```
+    ///
+    #[doc = codegen_section!(
+        header = "h5",
+        bench = "zero",
+        format = "coco",
+        arity = 3,
+        [
+            open
+            @index 1
+            @title "Sized"
+            @variant "static_size"
+        ],
+        [
+            @index 2
+            @title "Unsized"
+            @variant "dynamic_size"
+        ],
+        [
+            @index 3
+            @title "Dynamically Padded"
+            @variant "dynamic_padding"
+        ]
+    )]
+    #[inline(always)]
+    fn zero(&mut self) {
+        let slf: *mut Self = self;
+        let len = mem::size_of_val(self);
+        // SAFETY:
+        // - `self` is guaranteed by the type system to be valid for writes of
+        //   size `size_of_val(self)`.
+        // - `u8`'s alignment is 1, and thus `self` is guaranteed to be aligned
+        //   as required by `u8`.
+        // - Since `Self: FromZeros`, the all-zeros instance is a valid instance
+        //   of `Self.`
+        //
+        // FIXME(#429): Add references to docs and quotes.
+        unsafe { ptr::write_bytes(slf.cast::<u8>(), 0, len) };
+    }
+
+    /// Creates an instance of `Self` from zeroed bytes.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # use zerocopy::FromZeros;
+    /// # use zerocopy_derive::*;
+    /// #
+    /// #[derive(FromZeros)]
+    /// #[repr(C)]
+    /// struct PacketHeader {
+    ///     src_port: [u8; 2],
+    ///     dst_port: [u8; 2],
+    ///     length: [u8; 2],
+    ///     checksum: [u8; 2],
+    /// }
+    ///
+    /// let header: PacketHeader = FromZeros::new_zeroed();
+    ///
+    /// assert_eq!(header.src_port, [0, 0]);
+    /// assert_eq!(header.dst_port, [0, 0]);
+    /// assert_eq!(header.length, [0, 0]);
+    /// assert_eq!(header.checksum, [0, 0]);
+    /// ```
+    ///
+    #[doc = codegen_section!(
+        header = "h5",
+        bench = "new_zeroed",
+        format = "coco_static_size",
+    )]
+    #[must_use = "has no side effects"]
+    #[inline(always)]
+    fn new_zeroed() -> Self
+    where
+        Self: Sized,
+    {
+        // SAFETY: `FromZeros` says that the all-zeros bit pattern is legal.
+        unsafe { mem::zeroed() }
+    }
+
+    /// Creates a `Box<Self>` from zeroed bytes.
+    ///
+    /// This function is useful for allocating large values on the heap and
+    /// zero-initializing them, without ever creating a temporary instance of
+    /// `Self` on the stack. For example, `<[u8; 1048576]>::new_box_zeroed()`
+    /// will allocate `[u8; 1048576]` directly on the heap; it does not require
+    /// storing `[u8; 1048576]` in a temporary variable on the stack.
+    ///
+    /// On systems that use a heap implementation that supports allocating from
+    /// pre-zeroed memory, using `new_box_zeroed` (or related functions) may
+    /// have performance benefits.
+    ///
+    /// # Errors
+    ///
+    /// Returns an error on allocation failure. Allocation failure is guaranteed
+    /// never to cause a panic or an abort.
+    ///
+    #[doc = codegen_section!(
+        header = "h5",
+        bench = "new_box_zeroed",
+        format = "coco_static_size",
+    )]
+    #[must_use = "has no side effects (other than allocation)"]
+    #[cfg(any(feature = "alloc", test))]
+    #[cfg_attr(doc_cfg, doc(cfg(feature = "alloc")))]
+    #[inline]
+    fn new_box_zeroed() -> Result<Box<Self>, AllocError>
+    where
+        Self: Sized,
+    {
+        // If `T` is a ZST, then return a proper boxed instance of it. There is
+        // no allocation, but `Box` does require a correct dangling pointer.
+        let layout = Layout::new::<Self>();
+        if layout.size() == 0 {
+            // Construct the `Box` from a dangling pointer to avoid calling
+            // `Self::new_zeroed`. This ensures that stack space is never
+            // allocated for `Self` even on lower opt-levels where this branch
+            // might not get optimized out.
+
+            // SAFETY: Per [1], when `T` is a ZST, `Box<T>`'s only validity
+            // requirements are that the pointer is non-null and sufficiently
+            // aligned. Per [2], `NonNull::dangling` produces a pointer which
+            // is sufficiently aligned. Since the produced pointer is a
+            // `NonNull`, it is non-null.
+            //
+            // [1] Per https://doc.rust-lang.org/1.81.0/std/boxed/index.html#memory-layout:
+            //
+            //   For zero-sized values, the `Box` pointer has to be non-null and sufficiently aligned.
+            //
+            // [2] Per https://doc.rust-lang.org/std/ptr/struct.NonNull.html#method.dangling:
+            //
+            //   Creates a new `NonNull` that is dangling, but well-aligned.
+            return Ok(unsafe { Box::from_raw(NonNull::dangling().as_ptr()) });
+        }
+
+        // FIXME(#429): Add a "SAFETY" comment and remove this `allow`.
+        #[allow(clippy::undocumented_unsafe_blocks)]
+        let ptr = unsafe { alloc::alloc::alloc_zeroed(layout).cast::<Self>() };
+        if ptr.is_null() {
+            return Err(AllocError);
+        }
+        // FIXME(#429): Add a "SAFETY" comment and remove this `allow`.
+        #[allow(clippy::undocumented_unsafe_blocks)]
+        Ok(unsafe { Box::from_raw(ptr) })
+    }
+
+    /// Creates a `Box<[Self]>` (a boxed slice) from zeroed bytes.
+    ///
+    /// This function is useful for allocating large values of `[Self]` on the
+    /// heap and zero-initializing them, without ever creating a temporary
+    /// instance of `[Self; _]` on the stack. For example,
+    /// `u8::new_box_slice_zeroed(1048576)` will allocate the slice directly on
+    /// the heap; it does not require storing the slice on the stack.
+    ///
+    /// On systems that use a heap implementation that supports allocating from
+    /// pre-zeroed memory, using `new_box_slice_zeroed` may have performance
+    /// benefits.
+    ///
+    /// If `Self` is a zero-sized type, then this function will return a
+    /// `Box<[Self]>` that has the correct `len`. Such a box cannot contain any
+    /// actual information, but its `len()` property will report the correct
+    /// value.
+    ///
+    /// # Errors
+    ///
+    /// Returns an error on allocation failure. Allocation failure is
+    /// guaranteed never to cause a panic or an abort.
+    ///
+    #[doc = codegen_section!(
+        header = "h5",
+        bench = "new_box_zeroed_with_elems",
+        format = "coco",
+        arity = 2,
+        [
+            open
+            @index 1
+            @title "Unsized"
+            @variant "dynamic_size"
+        ],
+        [
+            @index 2
+            @title "Dynamically Padded"
+            @variant "dynamic_padding"
+        ]
+    )]
+    #[must_use = "has no side effects (other than allocation)"]
+    #[cfg(feature = "alloc")]
+    #[cfg_attr(doc_cfg, doc(cfg(feature = "alloc")))]
+    #[inline]
+    fn new_box_zeroed_with_elems(count: usize) -> Result<Box<Self>, AllocError>
+    where
+        Self: KnownLayout<PointerMetadata = usize>,
+    {
+        // SAFETY: `alloc::alloc::alloc_zeroed` is a valid argument of
+        // `new_box`. The referent of the pointer returned by `alloc_zeroed`
+        // (and, consequently, the `Box` derived from it) is a valid instance of
+        // `Self`, because `Self` is `FromZeros`.
+        unsafe { crate::util::new_box(count, alloc::alloc::alloc_zeroed) }
+    }
+
+    #[deprecated(since = "0.8.0", note = "renamed to `FromZeros::new_box_zeroed_with_elems`")]
+    #[doc(hidden)]
+    #[cfg(feature = "alloc")]
+    #[cfg_attr(doc_cfg, doc(cfg(feature = "alloc")))]
+    #[must_use = "has no side effects (other than allocation)"]
+    #[inline(always)]
+    fn new_box_slice_zeroed(len: usize) -> Result<Box<[Self]>, AllocError>
+    where
+        Self: Sized,
+    {
+        <[Self]>::new_box_zeroed_with_elems(len)
+    }
+
+    /// Creates a `Vec<Self>` from zeroed bytes.
+    ///
+    /// This function is useful for allocating large values of `Vec`s and
+    /// zero-initializing them, without ever creating a temporary instance of
+    /// `[Self; _]` (or many temporary instances of `Self`) on the stack. For
+    /// example, `u8::new_vec_zeroed(1048576)` will allocate directly on the
+    /// heap; it does not require storing intermediate values on the stack.
+    ///
+    /// On systems that use a heap implementation that supports allocating from
+    /// pre-zeroed memory, using `new_vec_zeroed` may have performance benefits.
+    ///
+    /// If `Self` is a zero-sized type, then this function will return a
+    /// `Vec<Self>` that has the correct `len`. Such a `Vec` cannot contain any
+    /// actual information, but its `len()` property will report the correct
+    /// value.
+    ///
+    /// # Errors
+    ///
+    /// Returns an error on allocation failure. Allocation failure is
+    /// guaranteed never to cause a panic or an abort.
+    ///
+    #[doc = codegen_section!(
+        header = "h5",
+        bench = "new_vec_zeroed",
+        format = "coco_static_size",
+    )]
+    #[must_use = "has no side effects (other than allocation)"]
+    #[cfg(feature = "alloc")]
+    #[cfg_attr(doc_cfg, doc(cfg(feature = "alloc")))]
+    #[inline(always)]
+    fn new_vec_zeroed(len: usize) -> Result<Vec<Self>, AllocError>
+    where
+        Self: Sized,
+    {
+        <[Self]>::new_box_zeroed_with_elems(len).map(Into::into)
+    }
+
+    /// Extends a `Vec<Self>` by pushing `additional` new items onto the end of
+    /// the vector. The new items are initialized with zeros.
+    ///
+    #[doc = codegen_section!(
+        header = "h5",
+        bench = "extend_vec_zeroed",
+        format = "coco_static_size",
+    )]
+    #[cfg(not(no_zerocopy_panic_in_const_and_vec_try_reserve_1_57_0))]
+    #[cfg(feature = "alloc")]
+    #[cfg_attr(doc_cfg, doc(cfg(all(rust = "1.57.0", feature = "alloc"))))]
+    #[inline(always)]
+    fn extend_vec_zeroed(v: &mut Vec<Self>, additional: usize) -> Result<(), AllocError>
+    where
+        Self: Sized,
+    {
+        // PANICS: We pass `v.len()` for `position`, so the `position > v.len()`
+        // panic condition is not satisfied.
+        <Self as FromZeros>::insert_vec_zeroed(v, v.len(), additional)
+    }
+
+    /// Inserts `additional` new items into `Vec<Self>` at `position`. The new
+    /// items are initialized with zeros.
+    ///
+    /// # Panics
+    ///
+    /// Panics if `position > v.len()`.
+    ///
+    #[doc = codegen_section!(
+        header = "h5",
+        bench = "insert_vec_zeroed",
+        format = "coco_static_size",
+    )]
+    #[cfg(not(no_zerocopy_panic_in_const_and_vec_try_reserve_1_57_0))]
+    #[cfg(feature = "alloc")]
+    #[cfg_attr(doc_cfg, doc(cfg(all(rust = "1.57.0", feature = "alloc"))))]
+    #[inline]
+    fn insert_vec_zeroed(
+        v: &mut Vec<Self>,
+        position: usize,
+        additional: usize,
+    ) -> Result<(), AllocError>
+    where
+        Self: Sized,
+    {
+        assert!(position <= v.len());
+        // We only conditionally compile on versions on which `try_reserve` is
+        // stable; the Clippy lint is a false positive.
+        v.try_reserve(additional).map_err(|_| AllocError)?;
+        // SAFETY: The `try_reserve` call guarantees that these cannot overflow:
+        // * `ptr.add(position)`
+        // * `position + additional`
+        // * `v.len() + additional`
+        //
+        // `v.len() - position` cannot overflow because we asserted that
+        // `position <= v.len()`.
+        #[allow(clippy::multiple_unsafe_ops_per_block)]
+        unsafe {
+            // This is a potentially overlapping copy.
+            let ptr = v.as_mut_ptr();
+            #[allow(clippy::arithmetic_side_effects)]
+            ptr.add(position).copy_to(ptr.add(position + additional), v.len() - position);
+            ptr.add(position).write_bytes(0, additional);
+            #[allow(clippy::arithmetic_side_effects)]
+            v.set_len(v.len() + additional);
+        }
+
+        Ok(())
+    }
+}
+
+/// Analyzes whether a type is [`FromBytes`].
+///
+/// This derive analyzes, at compile time, whether the annotated type satisfies
+/// the [safety conditions] of `FromBytes` and implements `FromBytes` and its
+/// supertraits if it is sound to do so. This derive can be applied to structs,
+/// enums, and unions;
+/// e.g.:
+///
+/// ```
+/// # use zerocopy_derive::{FromBytes, FromZeros, Immutable};
+/// #[derive(FromBytes)]
+/// struct MyStruct {
+/// # /*
+///     ...
+/// # */
+/// }
+///
+/// #[derive(FromBytes)]
+/// #[repr(u8)]
+/// enum MyEnum {
+/// #   V00, V01, V02, V03, V04, V05, V06, V07, V08, V09, V0A, V0B, V0C, V0D, V0E,
+/// #   V0F, V10, V11, V12, V13, V14, V15, V16, V17, V18, V19, V1A, V1B, V1C, V1D,
+/// #   V1E, V1F, V20, V21, V22, V23, V24, V25, V26, V27, V28, V29, V2A, V2B, V2C,
+/// #   V2D, V2E, V2F, V30, V31, V32, V33, V34, V35, V36, V37, V38, V39, V3A, V3B,
+/// #   V3C, V3D, V3E, V3F, V40, V41, V42, V43, V44, V45, V46, V47, V48, V49, V4A,
+/// #   V4B, V4C, V4D, V4E, V4F, V50, V51, V52, V53, V54, V55, V56, V57, V58, V59,
+/// #   V5A, V5B, V5C, V5D, V5E, V5F, V60, V61, V62, V63, V64, V65, V66, V67, V68,
+/// #   V69, V6A, V6B, V6C, V6D, V6E, V6F, V70, V71, V72, V73, V74, V75, V76, V77,
+/// #   V78, V79, V7A, V7B, V7C, V7D, V7E, V7F, V80, V81, V82, V83, V84, V85, V86,
+/// #   V87, V88, V89, V8A, V8B, V8C, V8D, V8E, V8F, V90, V91, V92, V93, V94, V95,
+/// #   V96, V97, V98, V99, V9A, V9B, V9C, V9D, V9E, V9F, VA0, VA1, VA2, VA3, VA4,
+/// #   VA5, VA6, VA7, VA8, VA9, VAA, VAB, VAC, VAD, VAE, VAF, VB0, VB1, VB2, VB3,
+/// #   VB4, VB5, VB6, VB7, VB8, VB9, VBA, VBB, VBC, VBD, VBE, VBF, VC0, VC1, VC2,
+/// #   VC3, VC4, VC5, VC6, VC7, VC8, VC9, VCA, VCB, VCC, VCD, VCE, VCF, VD0, VD1,
+/// #   VD2, VD3, VD4, VD5, VD6, VD7, VD8, VD9, VDA, VDB, VDC, VDD, VDE, VDF, VE0,
+/// #   VE1, VE2, VE3, VE4, VE5, VE6, VE7, VE8, VE9, VEA, VEB, VEC, VED, VEE, VEF,
+/// #   VF0, VF1, VF2, VF3, VF4, VF5, VF6, VF7, VF8, VF9, VFA, VFB, VFC, VFD, VFE,
+/// #   VFF,
+/// # /*
+///     ...
+/// # */
+/// }
+///
+/// #[derive(FromBytes, Immutable)]
+/// union MyUnion {
+/// #   variant: u8,
+/// # /*
+///     ...
+/// # */
+/// }
+/// ```
+///
+/// [safety conditions]: trait@FromBytes#safety
+///
+/// # Analysis
+///
+/// *This section describes, roughly, the analysis performed by this derive to
+/// determine whether it is sound to implement `FromBytes` for a given type.
+/// Unless you are modifying the implementation of this derive, or attempting to
+/// manually implement `FromBytes` for a type yourself, you don't need to read
+/// this section.*
+///
+/// If a type has the following properties, then this derive can implement
+/// `FromBytes` for that type:
+///
+/// - If the type is a struct, all of its fields must be `FromBytes`.
+/// - If the type is an enum:
+///   - It must have a defined representation which is one of `u8`, `u16`, `i8`,
+///     or `i16`.
+///   - The maximum number of discriminants must be used (so that every possible
+///     bit pattern is a valid one).
+///   - Its fields must be `FromBytes`.
+///
+/// This analysis is subject to change. Unsafe code may *only* rely on the
+/// documented [safety conditions] of `FromBytes`, and must *not* rely on the
+/// implementation details of this derive.
+///
+/// ## Why isn't an explicit representation required for structs?
+///
+/// Neither this derive, nor the [safety conditions] of `FromBytes`, requires
+/// that structs are marked with `#[repr(C)]`.
+///
+/// Per the [Rust reference](reference),
+///
+/// > The representation of a type can change the padding between fields, but
+/// > does not change the layout of the fields themselves.
+///
+/// [reference]: https://doc.rust-lang.org/reference/type-layout.html#representations
+///
+/// Since the layout of structs only consists of padding bytes and field bytes,
+/// a struct is soundly `FromBytes` if:
+/// 1. its padding is soundly `FromBytes`, and
+/// 2. its fields are soundly `FromBytes`.
+///
+/// The answer to the first question is always yes: padding bytes do not have
+/// any validity constraints. A [discussion] of this question in the Unsafe Code
+/// Guidelines Working Group concluded that it would be virtually unimaginable
+/// for future versions of rustc to add validity constraints to padding bytes.
+///
+/// [discussion]: https://github.com/rust-lang/unsafe-code-guidelines/issues/174
+///
+/// Whether a struct is soundly `FromBytes` therefore solely depends on whether
+/// its fields are `FromBytes`.
+#[cfg(any(feature = "derive", test))]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "derive")))]
+pub use zerocopy_derive::FromBytes;
+
+/// Types for which any bit pattern is valid.
+///
+/// Any memory region of the appropriate length which contains initialized bytes
+/// can be viewed as any `FromBytes` type with no runtime overhead. This is
+/// useful for efficiently parsing bytes as structured data.
+///
+/// # Warning: Padding bytes
+///
+/// Note that, when a value is moved or copied, only the non-padding bytes of
+/// that value are guaranteed to be preserved. It is unsound to assume that
+/// values written to padding bytes are preserved after a move or copy. For
+/// example, the following is unsound:
+///
+/// ```rust,no_run
+/// use core::mem::{size_of, transmute};
+/// use zerocopy::FromZeros;
+/// # use zerocopy_derive::*;
+///
+/// // Assume `Foo` is a type with padding bytes.
+/// #[derive(FromZeros, Default)]
+/// struct Foo {
+/// # /*
+///     ...
+/// # */
+/// }
+///
+/// let mut foo: Foo = Foo::default();
+/// FromZeros::zero(&mut foo);
+/// // UNSOUND: Although `FromZeros::zero` writes zeros to all bytes of `foo`,
+/// // those writes are not guaranteed to be preserved in padding bytes when
+/// // `foo` is moved, so this may expose padding bytes as `u8`s.
+/// let foo_bytes: [u8; size_of::<Foo>()] = unsafe { transmute(foo) };
+/// ```
+///
+/// # Implementation
+///
+/// **Do not implement this trait yourself!** Instead, use
+/// [`#[derive(FromBytes)]`][derive]; e.g.:
+///
+/// ```
+/// # use zerocopy_derive::{FromBytes, Immutable};
+/// #[derive(FromBytes)]
+/// struct MyStruct {
+/// # /*
+///     ...
+/// # */
+/// }
+///
+/// #[derive(FromBytes)]
+/// #[repr(u8)]
+/// enum MyEnum {
+/// #   V00, V01, V02, V03, V04, V05, V06, V07, V08, V09, V0A, V0B, V0C, V0D, V0E,
+/// #   V0F, V10, V11, V12, V13, V14, V15, V16, V17, V18, V19, V1A, V1B, V1C, V1D,
+/// #   V1E, V1F, V20, V21, V22, V23, V24, V25, V26, V27, V28, V29, V2A, V2B, V2C,
+/// #   V2D, V2E, V2F, V30, V31, V32, V33, V34, V35, V36, V37, V38, V39, V3A, V3B,
+/// #   V3C, V3D, V3E, V3F, V40, V41, V42, V43, V44, V45, V46, V47, V48, V49, V4A,
+/// #   V4B, V4C, V4D, V4E, V4F, V50, V51, V52, V53, V54, V55, V56, V57, V58, V59,
+/// #   V5A, V5B, V5C, V5D, V5E, V5F, V60, V61, V62, V63, V64, V65, V66, V67, V68,
+/// #   V69, V6A, V6B, V6C, V6D, V6E, V6F, V70, V71, V72, V73, V74, V75, V76, V77,
+/// #   V78, V79, V7A, V7B, V7C, V7D, V7E, V7F, V80, V81, V82, V83, V84, V85, V86,
+/// #   V87, V88, V89, V8A, V8B, V8C, V8D, V8E, V8F, V90, V91, V92, V93, V94, V95,
+/// #   V96, V97, V98, V99, V9A, V9B, V9C, V9D, V9E, V9F, VA0, VA1, VA2, VA3, VA4,
+/// #   VA5, VA6, VA7, VA8, VA9, VAA, VAB, VAC, VAD, VAE, VAF, VB0, VB1, VB2, VB3,
+/// #   VB4, VB5, VB6, VB7, VB8, VB9, VBA, VBB, VBC, VBD, VBE, VBF, VC0, VC1, VC2,
+/// #   VC3, VC4, VC5, VC6, VC7, VC8, VC9, VCA, VCB, VCC, VCD, VCE, VCF, VD0, VD1,
+/// #   VD2, VD3, VD4, VD5, VD6, VD7, VD8, VD9, VDA, VDB, VDC, VDD, VDE, VDF, VE0,
+/// #   VE1, VE2, VE3, VE4, VE5, VE6, VE7, VE8, VE9, VEA, VEB, VEC, VED, VEE, VEF,
+/// #   VF0, VF1, VF2, VF3, VF4, VF5, VF6, VF7, VF8, VF9, VFA, VFB, VFC, VFD, VFE,
+/// #   VFF,
+/// # /*
+///     ...
+/// # */
+/// }
+///
+/// #[derive(FromBytes, Immutable)]
+/// union MyUnion {
+/// #   variant: u8,
+/// # /*
+///     ...
+/// # */
+/// }
+/// ```
+///
+/// This derive performs a sophisticated, compile-time safety analysis to
+/// determine whether a type is `FromBytes`.
+///
+/// # Safety
+///
+/// *This section describes what is required in order for `T: FromBytes`, and
+/// what unsafe code may assume of such types. If you don't plan on implementing
+/// `FromBytes` manually, and you don't plan on writing unsafe code that
+/// operates on `FromBytes` types, then you don't need to read this section.*
+///
+/// If `T: FromBytes`, then unsafe code may assume that it is sound to produce a
+/// `T` whose bytes are initialized to any sequence of valid `u8`s (in other
+/// words, any byte value which is not uninitialized). If a type is marked as
+/// `FromBytes` which violates this contract, it may cause undefined behavior.
+///
+/// `#[derive(FromBytes)]` only permits [types which satisfy these
+/// requirements][derive-analysis].
+///
+#[cfg_attr(
+    feature = "derive",
+    doc = "[derive]: zerocopy_derive::FromBytes",
+    doc = "[derive-analysis]: zerocopy_derive::FromBytes#analysis"
+)]
+#[cfg_attr(
+    not(feature = "derive"),
+    doc = concat!("[derive]: https://docs.rs/zerocopy/", env!("CARGO_PKG_VERSION"), "/zerocopy/derive.FromBytes.html"),
+    doc = concat!("[derive-analysis]: https://docs.rs/zerocopy/", env!("CARGO_PKG_VERSION"), "/zerocopy/derive.FromBytes.html#analysis"),
+)]
+#[cfg_attr(
+    not(no_zerocopy_diagnostic_on_unimplemented_1_78_0),
+    diagnostic::on_unimplemented(note = "Consider adding `#[derive(FromBytes)]` to `{Self}`")
+)]
+pub unsafe trait FromBytes: FromZeros {
+    // The `Self: Sized` bound makes it so that `FromBytes` is still object
+    // safe.
+    #[doc(hidden)]
+    fn only_derive_is_allowed_to_implement_this_trait()
+    where
+        Self: Sized;
+
+    /// Interprets the given `source` as a `&Self`.
+    ///
+    /// This method attempts to return a reference to `source` interpreted as a
+    /// `Self`. If the length of `source` is not a [valid size of
+    /// `Self`][valid-size], or if `source` is not appropriately aligned, this
+    /// returns `Err`. If [`Self: Unaligned`][self-unaligned], you can
+    /// [infallibly discard the alignment error][size-error-from].
+    ///
+    /// `Self` may be a sized type, a slice, or a [slice DST][slice-dst].
+    ///
+    /// [valid-size]: crate::KnownLayout#what-is-a-valid-size
+    /// [self-unaligned]: Unaligned
+    /// [size-error-from]: error/struct.SizeError.html#method.from-1
+    /// [slice-dst]: KnownLayout#dynamically-sized-types
+    ///
+    /// # Compile-Time Assertions
+    ///
+    /// This method cannot yet be used on unsized types whose dynamically-sized
+    /// component is zero-sized. Attempting to use this method on such types
+    /// results in a compile-time assertion error; e.g.:
+    ///
+    /// ```compile_fail,E0080
+    /// use zerocopy::*;
+    /// # use zerocopy_derive::*;
+    ///
+    /// #[derive(FromBytes, Immutable, KnownLayout)]
+    /// #[repr(C)]
+    /// struct ZSTy {
+    ///     leading_sized: u16,
+    ///     trailing_dst: [()],
+    /// }
+    ///
+    /// let _ = ZSTy::ref_from_bytes(0u16.as_bytes()); // ⚠ Compile Error!
+    /// ```
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use zerocopy::FromBytes;
+    /// # use zerocopy_derive::*;
+    ///
+    /// #[derive(FromBytes, KnownLayout, Immutable)]
+    /// #[repr(C)]
+    /// struct PacketHeader {
+    ///     src_port: [u8; 2],
+    ///     dst_port: [u8; 2],
+    ///     length: [u8; 2],
+    ///     checksum: [u8; 2],
+    /// }
+    ///
+    /// #[derive(FromBytes, KnownLayout, Immutable)]
+    /// #[repr(C)]
+    /// struct Packet {
+    ///     header: PacketHeader,
+    ///     body: [u8],
+    /// }
+    ///
+    /// // These bytes encode a `Packet`.
+    /// let bytes = &[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11][..];
+    ///
+    /// let packet = Packet::ref_from_bytes(bytes).unwrap();
+    ///
+    /// assert_eq!(packet.header.src_port, [0, 1]);
+    /// assert_eq!(packet.header.dst_port, [2, 3]);
+    /// assert_eq!(packet.header.length, [4, 5]);
+    /// assert_eq!(packet.header.checksum, [6, 7]);
+    /// assert_eq!(packet.body, [8, 9, 10, 11]);
+    /// ```
+    ///
+    #[doc = codegen_section!(
+        header = "h5",
+        bench = "ref_from_bytes",
+        format = "coco",
+        arity = 3,
+        [
+            open
+            @index 1
+            @title "Sized"
+            @variant "static_size"
+        ],
+        [
+            @index 2
+            @title "Unsized"
+            @variant "dynamic_size"
+        ],
+        [
+            @index 3
+            @title "Dynamically Padded"
+            @variant "dynamic_padding"
+        ]
+    )]
+    #[must_use = "has no side effects"]
+    #[cfg_attr(zerocopy_inline_always, inline(always))]
+    #[cfg_attr(not(zerocopy_inline_always), inline)]
+    fn ref_from_bytes(source: &[u8]) -> Result<&Self, CastError<&[u8], Self>>
+    where
+        Self: KnownLayout + Immutable,
+    {
+        static_assert_dst_is_not_zst!(Self);
+        match Ptr::from_ref(source).try_cast_into_no_leftover::<_, BecauseImmutable>(None) {
+            Ok(ptr) => Ok(ptr.recall_validity().as_ref()),
+            Err(err) => Err(err.map_src(|src| src.as_ref())),
+        }
+    }
+
+    /// Interprets the prefix of the given `source` as a `&Self` without
+    /// copying.
+    ///
+    /// This method computes the [largest possible size of `Self`][valid-size]
+    /// that can fit in the leading bytes of `source`, then attempts to return
+    /// both a reference to those bytes interpreted as a `Self`, and a reference
+    /// to the remaining bytes. If there are insufficient bytes, or if `source`
+    /// is not appropriately aligned, this returns `Err`. If [`Self:
+    /// Unaligned`][self-unaligned], you can [infallibly discard the alignment
+    /// error][size-error-from].
+    ///
+    /// `Self` may be a sized type, a slice, or a [slice DST][slice-dst].
+    ///
+    /// [valid-size]: crate::KnownLayout#what-is-a-valid-size
+    /// [self-unaligned]: Unaligned
+    /// [size-error-from]: error/struct.SizeError.html#method.from-1
+    /// [slice-dst]: KnownLayout#dynamically-sized-types
+    ///
+    /// # Compile-Time Assertions
+    ///
+    /// This method cannot yet be used on unsized types whose dynamically-sized
+    /// component is zero-sized. See [`ref_from_prefix_with_elems`], which does
+    /// support such types. Attempting to use this method on such types results
+    /// in a compile-time assertion error; e.g.:
+    ///
+    /// ```compile_fail,E0080
+    /// use zerocopy::*;
+    /// # use zerocopy_derive::*;
+    ///
+    /// #[derive(FromBytes, Immutable, KnownLayout)]
+    /// #[repr(C)]
+    /// struct ZSTy {
+    ///     leading_sized: u16,
+    ///     trailing_dst: [()],
+    /// }
+    ///
+    /// let _ = ZSTy::ref_from_prefix(0u16.as_bytes()); // ⚠ Compile Error!
+    /// ```
+    ///
+    /// [`ref_from_prefix_with_elems`]: FromBytes::ref_from_prefix_with_elems
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use zerocopy::FromBytes;
+    /// # use zerocopy_derive::*;
+    ///
+    /// #[derive(FromBytes, KnownLayout, Immutable)]
+    /// #[repr(C)]
+    /// struct PacketHeader {
+    ///     src_port: [u8; 2],
+    ///     dst_port: [u8; 2],
+    ///     length: [u8; 2],
+    ///     checksum: [u8; 2],
+    /// }
+    ///
+    /// #[derive(FromBytes, KnownLayout, Immutable)]
+    /// #[repr(C)]
+    /// struct Packet {
+    ///     header: PacketHeader,
+    ///     body: [[u8; 2]],
+    /// }
+    ///
+    /// // These are more bytes than are needed to encode a `Packet`.
+    /// let bytes = &[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14][..];
+    ///
+    /// let (packet, suffix) = Packet::ref_from_prefix(bytes).unwrap();
+    ///
+    /// assert_eq!(packet.header.src_port, [0, 1]);
+    /// assert_eq!(packet.header.dst_port, [2, 3]);
+    /// assert_eq!(packet.header.length, [4, 5]);
+    /// assert_eq!(packet.header.checksum, [6, 7]);
+    /// assert_eq!(packet.body, [[8, 9], [10, 11], [12, 13]]);
+    /// assert_eq!(suffix, &[14u8][..]);
+    /// ```
+    ///
+    #[doc = codegen_section!(
+        header = "h5",
+        bench = "ref_from_prefix",
+        format = "coco",
+        arity = 3,
+        [
+            open
+            @index 1
+            @title "Sized"
+            @variant "static_size"
+        ],
+        [
+            @index 2
+            @title "Unsized"
+            @variant "dynamic_size"
+        ],
+        [
+            @index 3
+            @title "Dynamically Padded"
+            @variant "dynamic_padding"
+        ]
+    )]
+    #[must_use = "has no side effects"]
+    #[cfg_attr(zerocopy_inline_always, inline(always))]
+    #[cfg_attr(not(zerocopy_inline_always), inline)]
+    fn ref_from_prefix(source: &[u8]) -> Result<(&Self, &[u8]), CastError<&[u8], Self>>
+    where
+        Self: KnownLayout + Immutable,
+    {
+        static_assert_dst_is_not_zst!(Self);
+        ref_from_prefix_suffix(source, None, CastType::Prefix)
+    }
+
+    /// Interprets the suffix of the given bytes as a `&Self`.
+    ///
+    /// This method computes the [largest possible size of `Self`][valid-size]
+    /// that can fit in the trailing bytes of `source`, then attempts to return
+    /// both a reference to those bytes interpreted as a `Self`, and a reference
+    /// to the preceding bytes. If there are insufficient bytes, or if that
+    /// suffix of `source` is not appropriately aligned, this returns `Err`. If
+    /// [`Self: Unaligned`][self-unaligned], you can [infallibly discard the
+    /// alignment error][size-error-from].
+    ///
+    /// `Self` may be a sized type, a slice, or a [slice DST][slice-dst].
+    ///
+    /// [valid-size]: crate::KnownLayout#what-is-a-valid-size
+    /// [self-unaligned]: Unaligned
+    /// [size-error-from]: error/struct.SizeError.html#method.from-1
+    /// [slice-dst]: KnownLayout#dynamically-sized-types
+    ///
+    /// # Compile-Time Assertions
+    ///
+    /// This method cannot yet be used on unsized types whose dynamically-sized
+    /// component is zero-sized. See [`ref_from_suffix_with_elems`], which does
+    /// support such types. Attempting to use this method on such types results
+    /// in a compile-time assertion error; e.g.:
+    ///
+    /// ```compile_fail,E0080
+    /// use zerocopy::*;
+    /// # use zerocopy_derive::*;
+    ///
+    /// #[derive(FromBytes, Immutable, KnownLayout)]
+    /// #[repr(C)]
+    /// struct ZSTy {
+    ///     leading_sized: u16,
+    ///     trailing_dst: [()],
+    /// }
+    ///
+    /// let _ = ZSTy::ref_from_suffix(0u16.as_bytes()); // ⚠ Compile Error!
+    /// ```
+    ///
+    /// [`ref_from_suffix_with_elems`]: FromBytes::ref_from_suffix_with_elems
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use zerocopy::FromBytes;
+    /// # use zerocopy_derive::*;
+    ///
+    /// #[derive(FromBytes, Immutable, KnownLayout)]
+    /// #[repr(C)]
+    /// struct PacketTrailer {
+    ///     frame_check_sequence: [u8; 4],
+    /// }
+    ///
+    /// // These are more bytes than are needed to encode a `PacketTrailer`.
+    /// let bytes = &[0, 1, 2, 3, 4, 5, 6, 7, 8, 9][..];
+    ///
+    /// let (prefix, trailer) = PacketTrailer::ref_from_suffix(bytes).unwrap();
+    ///
+    /// assert_eq!(prefix, &[0, 1, 2, 3, 4, 5][..]);
+    /// assert_eq!(trailer.frame_check_sequence, [6, 7, 8, 9]);
+    /// ```
+    ///
+    #[doc = codegen_section!(
+        header = "h5",
+        bench = "ref_from_suffix",
+        format = "coco",
+        arity = 3,
+        [
+            open
+            @index 1
+            @title "Sized"
+            @variant "static_size"
+        ],
+        [
+            @index 2
+            @title "Unsized"
+            @variant "dynamic_size"
+        ],
+        [
+            @index 3
+            @title "Dynamically Padded"
+            @variant "dynamic_padding"
+        ]
+    )]
+    #[must_use = "has no side effects"]
+    #[cfg_attr(zerocopy_inline_always, inline(always))]
+    #[cfg_attr(not(zerocopy_inline_always), inline)]
+    fn ref_from_suffix(source: &[u8]) -> Result<(&[u8], &Self), CastError<&[u8], Self>>
+    where
+        Self: Immutable + KnownLayout,
+    {
+        static_assert_dst_is_not_zst!(Self);
+        ref_from_prefix_suffix(source, None, CastType::Suffix).map(swap)
+    }
+
+    /// Interprets the given `source` as a `&mut Self`.
+    ///
+    /// This method attempts to return a reference to `source` interpreted as a
+    /// `Self`. If the length of `source` is not a [valid size of
+    /// `Self`][valid-size], or if `source` is not appropriately aligned, this
+    /// returns `Err`. If [`Self: Unaligned`][self-unaligned], you can
+    /// [infallibly discard the alignment error][size-error-from].
+    ///
+    /// `Self` may be a sized type, a slice, or a [slice DST][slice-dst].
+    ///
+    /// [valid-size]: crate::KnownLayout#what-is-a-valid-size
+    /// [self-unaligned]: Unaligned
+    /// [size-error-from]: error/struct.SizeError.html#method.from-1
+    /// [slice-dst]: KnownLayout#dynamically-sized-types
+    ///
+    /// # Compile-Time Assertions
+    ///
+    /// This method cannot yet be used on unsized types whose dynamically-sized
+    /// component is zero-sized. See [`mut_from_prefix_with_elems`], which does
+    /// support such types. Attempting to use this method on such types results
+    /// in a compile-time assertion error; e.g.:
+    ///
+    /// ```compile_fail,E0080
+    /// use zerocopy::*;
+    /// # use zerocopy_derive::*;
+    ///
+    /// #[derive(FromBytes, Immutable, IntoBytes, KnownLayout)]
+    /// #[repr(C, packed)]
+    /// struct ZSTy {
+    ///     leading_sized: [u8; 2],
+    ///     trailing_dst: [()],
+    /// }
+    ///
+    /// let mut source = [85, 85];
+    /// let _ = ZSTy::mut_from_bytes(&mut source[..]); // ⚠ Compile Error!
+    /// ```
+    ///
+    /// [`mut_from_prefix_with_elems`]: FromBytes::mut_from_prefix_with_elems
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use zerocopy::FromBytes;
+    /// # use zerocopy_derive::*;
+    ///
+    /// #[derive(FromBytes, IntoBytes, KnownLayout, Immutable)]
+    /// #[repr(C)]
+    /// struct PacketHeader {
+    ///     src_port: [u8; 2],
+    ///     dst_port: [u8; 2],
+    ///     length: [u8; 2],
+    ///     checksum: [u8; 2],
+    /// }
+    ///
+    /// // These bytes encode a `PacketHeader`.
+    /// let bytes = &mut [0, 1, 2, 3, 4, 5, 6, 7][..];
+    ///
+    /// let header = PacketHeader::mut_from_bytes(bytes).unwrap();
+    ///
+    /// assert_eq!(header.src_port, [0, 1]);
+    /// assert_eq!(header.dst_port, [2, 3]);
+    /// assert_eq!(header.length, [4, 5]);
+    /// assert_eq!(header.checksum, [6, 7]);
+    ///
+    /// header.checksum = [0, 0];
+    ///
+    /// assert_eq!(bytes, [0, 1, 2, 3, 4, 5, 0, 0]);
+    ///
+    /// ```
+    ///
+    #[doc = codegen_header!("h5", "mut_from_bytes")]
+    ///
+    /// See [`FromBytes::ref_from_bytes`](#method.ref_from_bytes.codegen).
+    #[must_use = "has no side effects"]
+    #[cfg_attr(zerocopy_inline_always, inline(always))]
+    #[cfg_attr(not(zerocopy_inline_always), inline)]
+    fn mut_from_bytes(source: &mut [u8]) -> Result<&mut Self, CastError<&mut [u8], Self>>
+    where
+        Self: IntoBytes + KnownLayout,
+    {
+        static_assert_dst_is_not_zst!(Self);
+        match Ptr::from_mut(source).try_cast_into_no_leftover::<_, BecauseExclusive>(None) {
+            Ok(ptr) => Ok(ptr.recall_validity::<_, (_, (_, _))>().as_mut()),
+            Err(err) => Err(err.map_src(|src| src.as_mut())),
+        }
+    }
+
+    /// Interprets the prefix of the given `source` as a `&mut Self` without
+    /// copying.
+    ///
+    /// This method computes the [largest possible size of `Self`][valid-size]
+    /// that can fit in the leading bytes of `source`, then attempts to return
+    /// both a reference to those bytes interpreted as a `Self`, and a reference
+    /// to the remaining bytes. If there are insufficient bytes, or if `source`
+    /// is not appropriately aligned, this returns `Err`. If [`Self:
+    /// Unaligned`][self-unaligned], you can [infallibly discard the alignment
+    /// error][size-error-from].
+    ///
+    /// `Self` may be a sized type, a slice, or a [slice DST][slice-dst].
+    ///
+    /// [valid-size]: crate::KnownLayout#what-is-a-valid-size
+    /// [self-unaligned]: Unaligned
+    /// [size-error-from]: error/struct.SizeError.html#method.from-1
+    /// [slice-dst]: KnownLayout#dynamically-sized-types
+    ///
+    /// # Compile-Time Assertions
+    ///
+    /// This method cannot yet be used on unsized types whose dynamically-sized
+    /// component is zero-sized. See [`mut_from_suffix_with_elems`], which does
+    /// support such types. Attempting to use this method on such types results
+    /// in a compile-time assertion error; e.g.:
+    ///
+    /// ```compile_fail,E0080
+    /// use zerocopy::*;
+    /// # use zerocopy_derive::*;
+    ///
+    /// #[derive(FromBytes, Immutable, IntoBytes, KnownLayout)]
+    /// #[repr(C, packed)]
+    /// struct ZSTy {
+    ///     leading_sized: [u8; 2],
+    ///     trailing_dst: [()],
+    /// }
+    ///
+    /// let mut source = [85, 85];
+    /// let _ = ZSTy::mut_from_prefix(&mut source[..]); // ⚠ Compile Error!
+    /// ```
+    ///
+    /// [`mut_from_suffix_with_elems`]: FromBytes::mut_from_suffix_with_elems
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use zerocopy::FromBytes;
+    /// # use zerocopy_derive::*;
+    ///
+    /// #[derive(FromBytes, IntoBytes, KnownLayout, Immutable)]
+    /// #[repr(C)]
+    /// struct PacketHeader {
+    ///     src_port: [u8; 2],
+    ///     dst_port: [u8; 2],
+    ///     length: [u8; 2],
+    ///     checksum: [u8; 2],
+    /// }
+    ///
+    /// // These are more bytes than are needed to encode a `PacketHeader`.
+    /// let bytes = &mut [0, 1, 2, 3, 4, 5, 6, 7, 8, 9][..];
+    ///
+    /// let (header, body) = PacketHeader::mut_from_prefix(bytes).unwrap();
+    ///
+    /// assert_eq!(header.src_port, [0, 1]);
+    /// assert_eq!(header.dst_port, [2, 3]);
+    /// assert_eq!(header.length, [4, 5]);
+    /// assert_eq!(header.checksum, [6, 7]);
+    /// assert_eq!(body, &[8, 9][..]);
+    ///
+    /// header.checksum = [0, 0];
+    /// body.fill(1);
+    ///
+    /// assert_eq!(bytes, [0, 1, 2, 3, 4, 5, 0, 0, 1, 1]);
+    /// ```
+    ///
+    #[doc = codegen_header!("h5", "mut_from_prefix")]
+    ///
+    /// See [`FromBytes::ref_from_prefix`](#method.ref_from_prefix.codegen).
+    #[must_use = "has no side effects"]
+    #[cfg_attr(zerocopy_inline_always, inline(always))]
+    #[cfg_attr(not(zerocopy_inline_always), inline)]
+    fn mut_from_prefix(
+        source: &mut [u8],
+    ) -> Result<(&mut Self, &mut [u8]), CastError<&mut [u8], Self>>
+    where
+        Self: IntoBytes + KnownLayout,
+    {
+        static_assert_dst_is_not_zst!(Self);
+        mut_from_prefix_suffix(source, None, CastType::Prefix)
+    }
+
+    /// Interprets the suffix of the given `source` as a `&mut Self` without
+    /// copying.
+    ///
+    /// This method computes the [largest possible size of `Self`][valid-size]
+    /// that can fit in the trailing bytes of `source`, then attempts to return
+    /// both a reference to those bytes interpreted as a `Self`, and a reference
+    /// to the preceding bytes. If there are insufficient bytes, or if that
+    /// suffix of `source` is not appropriately aligned, this returns `Err`. If
+    /// [`Self: Unaligned`][self-unaligned], you can [infallibly discard the
+    /// alignment error][size-error-from].
+    ///
+    /// `Self` may be a sized type, a slice, or a [slice DST][slice-dst].
+    ///
+    /// [valid-size]: crate::KnownLayout#what-is-a-valid-size
+    /// [self-unaligned]: Unaligned
+    /// [size-error-from]: error/struct.SizeError.html#method.from-1
+    /// [slice-dst]: KnownLayout#dynamically-sized-types
+    ///
+    /// # Compile-Time Assertions
+    ///
+    /// This method cannot yet be used on unsized types whose dynamically-sized
+    /// component is zero-sized. Attempting to use this method on such types
+    /// results in a compile-time assertion error; e.g.:
+    ///
+    /// ```compile_fail,E0080
+    /// use zerocopy::*;
+    /// # use zerocopy_derive::*;
+    ///
+    /// #[derive(FromBytes, Immutable, IntoBytes, KnownLayout)]
+    /// #[repr(C, packed)]
+    /// struct ZSTy {
+    ///     leading_sized: [u8; 2],
+    ///     trailing_dst: [()],
+    /// }
+    ///
+    /// let mut source = [85, 85];
+    /// let _ = ZSTy::mut_from_suffix(&mut source[..]); // ⚠ Compile Error!
+    /// ```
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use zerocopy::FromBytes;
+    /// # use zerocopy_derive::*;
+    ///
+    /// #[derive(FromBytes, IntoBytes, KnownLayout, Immutable)]
+    /// #[repr(C)]
+    /// struct PacketTrailer {
+    ///     frame_check_sequence: [u8; 4],
+    /// }
+    ///
+    /// // These are more bytes than are needed to encode a `PacketTrailer`.
+    /// let bytes = &mut [0, 1, 2, 3, 4, 5, 6, 7, 8, 9][..];
+    ///
+    /// let (prefix, trailer) = PacketTrailer::mut_from_suffix(bytes).unwrap();
+    ///
+    /// assert_eq!(prefix, &[0u8, 1, 2, 3, 4, 5][..]);
+    /// assert_eq!(trailer.frame_check_sequence, [6, 7, 8, 9]);
+    ///
+    /// prefix.fill(0);
+    /// trailer.frame_check_sequence.fill(1);
+    ///
+    /// assert_eq!(bytes, [0, 0, 0, 0, 0, 0, 1, 1, 1, 1]);
+    /// ```
+    ///
+    #[doc = codegen_header!("h5", "mut_from_suffix")]
+    ///
+    /// See [`FromBytes::ref_from_suffix`](#method.ref_from_suffix.codegen).
+    #[must_use = "has no side effects"]
+    #[cfg_attr(zerocopy_inline_always, inline(always))]
+    #[cfg_attr(not(zerocopy_inline_always), inline)]
+    fn mut_from_suffix(
+        source: &mut [u8],
+    ) -> Result<(&mut [u8], &mut Self), CastError<&mut [u8], Self>>
+    where
+        Self: IntoBytes + KnownLayout,
+    {
+        static_assert_dst_is_not_zst!(Self);
+        mut_from_prefix_suffix(source, None, CastType::Suffix).map(swap)
+    }
+
+    /// Interprets the given `source` as a `&Self` with a DST length equal to
+    /// `count`.
+    ///
+    /// This method attempts to return a reference to `source` interpreted as a
+    /// `Self` with `count` trailing elements. If the length of `source` is not
+    /// equal to the size of `Self` with `count` elements, or if `source` is not
+    /// appropriately aligned, this returns `Err`. If [`Self:
+    /// Unaligned`][self-unaligned], you can [infallibly discard the alignment
+    /// error][size-error-from].
+    ///
+    /// [self-unaligned]: Unaligned
+    /// [size-error-from]: error/struct.SizeError.html#method.from-1
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use zerocopy::FromBytes;
+    /// # use zerocopy_derive::*;
+    ///
+    /// # #[derive(Debug, PartialEq, Eq)]
+    /// #[derive(FromBytes, Immutable)]
+    /// #[repr(C)]
+    /// struct Pixel {
+    ///     r: u8,
+    ///     g: u8,
+    ///     b: u8,
+    ///     a: u8,
+    /// }
+    ///
+    /// let bytes = &[0, 1, 2, 3, 4, 5, 6, 7][..];
+    ///
+    /// let pixels = <[Pixel]>::ref_from_bytes_with_elems(bytes, 2).unwrap();
+    ///
+    /// assert_eq!(pixels, &[
+    ///     Pixel { r: 0, g: 1, b: 2, a: 3 },
+    ///     Pixel { r: 4, g: 5, b: 6, a: 7 },
+    /// ]);
+    ///
+    /// ```
+    ///
+    /// Since an explicit `count` is provided, this method supports types with
+    /// zero-sized trailing slice elements. Methods such as [`ref_from_bytes`]
+    /// which do not take an explicit count do not support such types.
+    ///
+    /// ```
+    /// use zerocopy::*;
+    /// # use zerocopy_derive::*;
+    ///
+    /// #[derive(FromBytes, Immutable, KnownLayout)]
+    /// #[repr(C)]
+    /// struct ZSTy {
+    ///     leading_sized: [u8; 2],
+    ///     trailing_dst: [()],
+    /// }
+    ///
+    /// let src = &[85, 85][..];
+    /// let zsty = ZSTy::ref_from_bytes_with_elems(src, 42).unwrap();
+    /// assert_eq!(zsty.trailing_dst.len(), 42);
+    /// ```
+    ///
+    /// [`ref_from_bytes`]: FromBytes::ref_from_bytes
+    ///
+    #[doc = codegen_section!(
+        header = "h5",
+        bench = "ref_from_bytes_with_elems",
+        format = "coco",
+        arity = 2,
+        [
+            open
+            @index 1
+            @title "Unsized"
+            @variant "dynamic_size"
+        ],
+        [
+            @index 2
+            @title "Dynamically Padded"
+            @variant "dynamic_padding"
+        ]
+    )]
+    #[must_use = "has no side effects"]
+    #[cfg_attr(zerocopy_inline_always, inline(always))]
+    #[cfg_attr(not(zerocopy_inline_always), inline)]
+    fn ref_from_bytes_with_elems(
+        source: &[u8],
+        count: usize,
+    ) -> Result<&Self, CastError<&[u8], Self>>
+    where
+        Self: KnownLayout<PointerMetadata = usize> + Immutable,
+    {
+        let source = Ptr::from_ref(source);
+        let maybe_slf = source.try_cast_into_no_leftover::<_, BecauseImmutable>(Some(count));
+        match maybe_slf {
+            Ok(slf) => Ok(slf.recall_validity().as_ref()),
+            Err(err) => Err(err.map_src(|s| s.as_ref())),
+        }
+    }
+
+    /// Interprets the prefix of the given `source` as a DST `&Self` with length
+    /// equal to `count`.
+    ///
+    /// This method attempts to return a reference to the prefix of `source`
+    /// interpreted as a `Self` with `count` trailing elements, and a reference
+    /// to the remaining bytes. If there are insufficient bytes, or if `source`
+    /// is not appropriately aligned, this returns `Err`. If [`Self:
+    /// Unaligned`][self-unaligned], you can [infallibly discard the alignment
+    /// error][size-error-from].
+    ///
+    /// [self-unaligned]: Unaligned
+    /// [size-error-from]: error/struct.SizeError.html#method.from-1
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use zerocopy::FromBytes;
+    /// # use zerocopy_derive::*;
+    ///
+    /// # #[derive(Debug, PartialEq, Eq)]
+    /// #[derive(FromBytes, Immutable)]
+    /// #[repr(C)]
+    /// struct Pixel {
+    ///     r: u8,
+    ///     g: u8,
+    ///     b: u8,
+    ///     a: u8,
+    /// }
+    ///
+    /// // These are more bytes than are needed to encode two `Pixel`s.
+    /// let bytes = &[0, 1, 2, 3, 4, 5, 6, 7, 8, 9][..];
+    ///
+    /// let (pixels, suffix) = <[Pixel]>::ref_from_prefix_with_elems(bytes, 2).unwrap();
+    ///
+    /// assert_eq!(pixels, &[
+    ///     Pixel { r: 0, g: 1, b: 2, a: 3 },
+    ///     Pixel { r: 4, g: 5, b: 6, a: 7 },
+    /// ]);
+    ///
+    /// assert_eq!(suffix, &[8, 9]);
+    /// ```
+    ///
+    /// Since an explicit `count` is provided, this method supports types with
+    /// zero-sized trailing slice elements. Methods such as [`ref_from_prefix`]
+    /// which do not take an explicit count do not support such types.
+    ///
+    /// ```
+    /// use zerocopy::*;
+    /// # use zerocopy_derive::*;
+    ///
+    /// #[derive(FromBytes, Immutable, KnownLayout)]
+    /// #[repr(C)]
+    /// struct ZSTy {
+    ///     leading_sized: [u8; 2],
+    ///     trailing_dst: [()],
+    /// }
+    ///
+    /// let src = &[85, 85][..];
+    /// let (zsty, _) = ZSTy::ref_from_prefix_with_elems(src, 42).unwrap();
+    /// assert_eq!(zsty.trailing_dst.len(), 42);
+    /// ```
+    ///
+    /// [`ref_from_prefix`]: FromBytes::ref_from_prefix
+    ///
+    #[doc = codegen_section!(
+        header = "h5",
+        bench = "ref_from_prefix_with_elems",
+        format = "coco",
+        arity = 2,
+        [
+            open
+            @index 1
+            @title "Unsized"
+            @variant "dynamic_size"
+        ],
+        [
+            @index 2
+            @title "Dynamically Padded"
+            @variant "dynamic_padding"
+        ]
+    )]
+    #[must_use = "has no side effects"]
+    #[cfg_attr(zerocopy_inline_always, inline(always))]
+    #[cfg_attr(not(zerocopy_inline_always), inline)]
+    fn ref_from_prefix_with_elems(
+        source: &[u8],
+        count: usize,
+    ) -> Result<(&Self, &[u8]), CastError<&[u8], Self>>
+    where
+        Self: KnownLayout<PointerMetadata = usize> + Immutable,
+    {
+        ref_from_prefix_suffix(source, Some(count), CastType::Prefix)
+    }
+
+    /// Interprets the suffix of the given `source` as a DST `&Self` with length
+    /// equal to `count`.
+    ///
+    /// This method attempts to return a reference to the suffix of `source`
+    /// interpreted as a `Self` with `count` trailing elements, and a reference
+    /// to the preceding bytes. If there are insufficient bytes, or if that
+    /// suffix of `source` is not appropriately aligned, this returns `Err`. If
+    /// [`Self: Unaligned`][self-unaligned], you can [infallibly discard the
+    /// alignment error][size-error-from].
+    ///
+    /// [self-unaligned]: Unaligned
+    /// [size-error-from]: error/struct.SizeError.html#method.from-1
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use zerocopy::FromBytes;
+    /// # use zerocopy_derive::*;
+    ///
+    /// # #[derive(Debug, PartialEq, Eq)]
+    /// #[derive(FromBytes, Immutable)]
+    /// #[repr(C)]
+    /// struct Pixel {
+    ///     r: u8,
+    ///     g: u8,
+    ///     b: u8,
+    ///     a: u8,
+    /// }
+    ///
+    /// // These are more bytes than are needed to encode two `Pixel`s.
+    /// let bytes = &[0, 1, 2, 3, 4, 5, 6, 7, 8, 9][..];
+    ///
+    /// let (prefix, pixels) = <[Pixel]>::ref_from_suffix_with_elems(bytes, 2).unwrap();
+    ///
+    /// assert_eq!(prefix, &[0, 1]);
+    ///
+    /// assert_eq!(pixels, &[
+    ///     Pixel { r: 2, g: 3, b: 4, a: 5 },
+    ///     Pixel { r: 6, g: 7, b: 8, a: 9 },
+    /// ]);
+    /// ```
+    ///
+    /// Since an explicit `count` is provided, this method supports types with
+    /// zero-sized trailing slice elements. Methods such as [`ref_from_suffix`]
+    /// which do not take an explicit count do not support such types.
+    ///
+    /// ```
+    /// use zerocopy::*;
+    /// # use zerocopy_derive::*;
+    ///
+    /// #[derive(FromBytes, Immutable, KnownLayout)]
+    /// #[repr(C)]
+    /// struct ZSTy {
+    ///     leading_sized: [u8; 2],
+    ///     trailing_dst: [()],
+    /// }
+    ///
+    /// let src = &[85, 85][..];
+    /// let (_, zsty) = ZSTy::ref_from_suffix_with_elems(src, 42).unwrap();
+    /// assert_eq!(zsty.trailing_dst.len(), 42);
+    /// ```
+    ///
+    /// [`ref_from_suffix`]: FromBytes::ref_from_suffix
+    ///
+    #[doc = codegen_section!(
+        header = "h5",
+        bench = "ref_from_suffix_with_elems",
+        format = "coco",
+        arity = 2,
+        [
+            open
+            @index 1
+            @title "Unsized"
+            @variant "dynamic_size"
+        ],
+        [
+            @index 2
+            @title "Dynamically Padded"
+            @variant "dynamic_padding"
+        ]
+    )]
+    #[must_use = "has no side effects"]
+    #[cfg_attr(zerocopy_inline_always, inline(always))]
+    #[cfg_attr(not(zerocopy_inline_always), inline)]
+    fn ref_from_suffix_with_elems(
+        source: &[u8],
+        count: usize,
+    ) -> Result<(&[u8], &Self), CastError<&[u8], Self>>
+    where
+        Self: KnownLayout<PointerMetadata = usize> + Immutable,
+    {
+        ref_from_prefix_suffix(source, Some(count), CastType::Suffix).map(swap)
+    }
+
+    /// Interprets the given `source` as a `&mut Self` with a DST length equal
+    /// to `count`.
+    ///
+    /// This method attempts to return a reference to `source` interpreted as a
+    /// `Self` with `count` trailing elements. If the length of `source` is not
+    /// equal to the size of `Self` with `count` elements, or if `source` is not
+    /// appropriately aligned, this returns `Err`. If [`Self:
+    /// Unaligned`][self-unaligned], you can [infallibly discard the alignment
+    /// error][size-error-from].
+    ///
+    /// [self-unaligned]: Unaligned
+    /// [size-error-from]: error/struct.SizeError.html#method.from-1
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use zerocopy::FromBytes;
+    /// # use zerocopy_derive::*;
+    ///
+    /// # #[derive(Debug, PartialEq, Eq)]
+    /// #[derive(KnownLayout, FromBytes, IntoBytes, Immutable)]
+    /// #[repr(C)]
+    /// struct Pixel {
+    ///     r: u8,
+    ///     g: u8,
+    ///     b: u8,
+    ///     a: u8,
+    /// }
+    ///
+    /// let bytes = &mut [0, 1, 2, 3, 4, 5, 6, 7][..];
+    ///
+    /// let pixels = <[Pixel]>::mut_from_bytes_with_elems(bytes, 2).unwrap();
+    ///
+    /// assert_eq!(pixels, &[
+    ///     Pixel { r: 0, g: 1, b: 2, a: 3 },
+    ///     Pixel { r: 4, g: 5, b: 6, a: 7 },
+    /// ]);
+    ///
+    /// pixels[1] = Pixel { r: 0, g: 0, b: 0, a: 0 };
+    ///
+    /// assert_eq!(bytes, [0, 1, 2, 3, 0, 0, 0, 0]);
+    /// ```
+    ///
+    /// Since an explicit `count` is provided, this method supports types with
+    /// zero-sized trailing slice elements. Methods such as [`mut_from_bytes`]
+    /// which do not take an explicit count do not support such types.
+    ///
+    /// ```
+    /// use zerocopy::*;
+    /// # use zerocopy_derive::*;
+    ///
+    /// #[derive(FromBytes, IntoBytes, Immutable, KnownLayout)]
+    /// #[repr(C, packed)]
+    /// struct ZSTy {
+    ///     leading_sized: [u8; 2],
+    ///     trailing_dst: [()],
+    /// }
+    ///
+    /// let src = &mut [85, 85][..];
+    /// let zsty = ZSTy::mut_from_bytes_with_elems(src, 42).unwrap();
+    /// assert_eq!(zsty.trailing_dst.len(), 42);
+    /// ```
+    ///
+    /// [`mut_from_bytes`]: FromBytes::mut_from_bytes
+    ///
+    #[doc = codegen_header!("h5", "mut_from_bytes_with_elems")]
+    ///
+    /// See [`TryFromBytes::ref_from_bytes_with_elems`](#method.ref_from_bytes_with_elems.codegen).
+    #[must_use = "has no side effects"]
+    #[cfg_attr(zerocopy_inline_always, inline(always))]
+    #[cfg_attr(not(zerocopy_inline_always), inline)]
+    fn mut_from_bytes_with_elems(
+        source: &mut [u8],
+        count: usize,
+    ) -> Result<&mut Self, CastError<&mut [u8], Self>>
+    where
+        Self: IntoBytes + KnownLayout<PointerMetadata = usize> + Immutable,
+    {
+        let source = Ptr::from_mut(source);
+        let maybe_slf = source.try_cast_into_no_leftover::<_, BecauseImmutable>(Some(count));
+        match maybe_slf {
+            Ok(slf) => Ok(slf.recall_validity::<_, (_, (_, BecauseExclusive))>().as_mut()),
+            Err(err) => Err(err.map_src(|s| s.as_mut())),
+        }
+    }
+
+    /// Interprets the prefix of the given `source` as a `&mut Self` with DST
+    /// length equal to `count`.
+    ///
+    /// This method attempts to return a reference to the prefix of `source`
+    /// interpreted as a `Self` with `count` trailing elements, and a reference
+    /// to the preceding bytes. If there are insufficient bytes, or if `source`
+    /// is not appropriately aligned, this returns `Err`. If [`Self:
+    /// Unaligned`][self-unaligned], you can [infallibly discard the alignment
+    /// error][size-error-from].
+    ///
+    /// [self-unaligned]: Unaligned
+    /// [size-error-from]: error/struct.SizeError.html#method.from-1
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use zerocopy::FromBytes;
+    /// # use zerocopy_derive::*;
+    ///
+    /// # #[derive(Debug, PartialEq, Eq)]
+    /// #[derive(KnownLayout, FromBytes, IntoBytes, Immutable)]
+    /// #[repr(C)]
+    /// struct Pixel {
+    ///     r: u8,
+    ///     g: u8,
+    ///     b: u8,
+    ///     a: u8,
+    /// }
+    ///
+    /// // These are more bytes than are needed to encode two `Pixel`s.
+    /// let bytes = &mut [0, 1, 2, 3, 4, 5, 6, 7, 8, 9][..];
+    ///
+    /// let (pixels, suffix) = <[Pixel]>::mut_from_prefix_with_elems(bytes, 2).unwrap();
+    ///
+    /// assert_eq!(pixels, &[
+    ///     Pixel { r: 0, g: 1, b: 2, a: 3 },
+    ///     Pixel { r: 4, g: 5, b: 6, a: 7 },
+    /// ]);
+    ///
+    /// assert_eq!(suffix, &[8, 9]);
+    ///
+    /// pixels[1] = Pixel { r: 0, g: 0, b: 0, a: 0 };
+    /// suffix.fill(1);
+    ///
+    /// assert_eq!(bytes, [0, 1, 2, 3, 0, 0, 0, 0, 1, 1]);
+    /// ```
+    ///
+    /// Since an explicit `count` is provided, this method supports types with
+    /// zero-sized trailing slice elements. Methods such as [`mut_from_prefix`]
+    /// which do not take an explicit count do not support such types.
+    ///
+    /// ```
+    /// use zerocopy::*;
+    /// # use zerocopy_derive::*;
+    ///
+    /// #[derive(FromBytes, IntoBytes, Immutable, KnownLayout)]
+    /// #[repr(C, packed)]
+    /// struct ZSTy {
+    ///     leading_sized: [u8; 2],
+    ///     trailing_dst: [()],
+    /// }
+    ///
+    /// let src = &mut [85, 85][..];
+    /// let (zsty, _) = ZSTy::mut_from_prefix_with_elems(src, 42).unwrap();
+    /// assert_eq!(zsty.trailing_dst.len(), 42);
+    /// ```
+    ///
+    /// [`mut_from_prefix`]: FromBytes::mut_from_prefix
+    ///
+    #[doc = codegen_header!("h5", "mut_from_prefix_with_elems")]
+    ///
+    /// See [`TryFromBytes::ref_from_prefix_with_elems`](#method.ref_from_prefix_with_elems.codegen).
+    #[must_use = "has no side effects"]
+    #[cfg_attr(zerocopy_inline_always, inline(always))]
+    #[cfg_attr(not(zerocopy_inline_always), inline)]
+    fn mut_from_prefix_with_elems(
+        source: &mut [u8],
+        count: usize,
+    ) -> Result<(&mut Self, &mut [u8]), CastError<&mut [u8], Self>>
+    where
+        Self: IntoBytes + KnownLayout<PointerMetadata = usize>,
+    {
+        mut_from_prefix_suffix(source, Some(count), CastType::Prefix)
+    }
+
+    /// Interprets the suffix of the given `source` as a `&mut Self` with DST
+    /// length equal to `count`.
+    ///
+    /// This method attempts to return a reference to the suffix of `source`
+    /// interpreted as a `Self` with `count` trailing elements, and a reference
+    /// to the remaining bytes. If there are insufficient bytes, or if that
+    /// suffix of `source` is not appropriately aligned, this returns `Err`. If
+    /// [`Self: Unaligned`][self-unaligned], you can [infallibly discard the
+    /// alignment error][size-error-from].
+    ///
+    /// [self-unaligned]: Unaligned
+    /// [size-error-from]: error/struct.SizeError.html#method.from-1
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use zerocopy::FromBytes;
+    /// # use zerocopy_derive::*;
+    ///
+    /// # #[derive(Debug, PartialEq, Eq)]
+    /// #[derive(FromBytes, IntoBytes, Immutable)]
+    /// #[repr(C)]
+    /// struct Pixel {
+    ///     r: u8,
+    ///     g: u8,
+    ///     b: u8,
+    ///     a: u8,
+    /// }
+    ///
+    /// // These are more bytes than are needed to encode two `Pixel`s.
+    /// let bytes = &mut [0, 1, 2, 3, 4, 5, 6, 7, 8, 9][..];
+    ///
+    /// let (prefix, pixels) = <[Pixel]>::mut_from_suffix_with_elems(bytes, 2).unwrap();
+    ///
+    /// assert_eq!(prefix, &[0, 1]);
+    ///
+    /// assert_eq!(pixels, &[
+    ///     Pixel { r: 2, g: 3, b: 4, a: 5 },
+    ///     Pixel { r: 6, g: 7, b: 8, a: 9 },
+    /// ]);
+    ///
+    /// prefix.fill(9);
+    /// pixels[1] = Pixel { r: 0, g: 0, b: 0, a: 0 };
+    ///
+    /// assert_eq!(bytes, [9, 9, 2, 3, 4, 5, 0, 0, 0, 0]);
+    /// ```
+    ///
+    /// Since an explicit `count` is provided, this method supports types with
+    /// zero-sized trailing slice elements. Methods such as [`mut_from_suffix`]
+    /// which do not take an explicit count do not support such types.
+    ///
+    /// ```
+    /// use zerocopy::*;
+    /// # use zerocopy_derive::*;
+    ///
+    /// #[derive(FromBytes, IntoBytes, Immutable, KnownLayout)]
+    /// #[repr(C, packed)]
+    /// struct ZSTy {
+    ///     leading_sized: [u8; 2],
+    ///     trailing_dst: [()],
+    /// }
+    ///
+    /// let src = &mut [85, 85][..];
+    /// let (_, zsty) = ZSTy::mut_from_suffix_with_elems(src, 42).unwrap();
+    /// assert_eq!(zsty.trailing_dst.len(), 42);
+    /// ```
+    ///
+    /// [`mut_from_suffix`]: FromBytes::mut_from_suffix
+    ///
+    #[doc = codegen_header!("h5", "mut_from_suffix_with_elems")]
+    ///
+    /// See [`TryFromBytes::ref_from_suffix_with_elems`](#method.ref_from_suffix_with_elems.codegen).
+    #[must_use = "has no side effects"]
+    #[cfg_attr(zerocopy_inline_always, inline(always))]
+    #[cfg_attr(not(zerocopy_inline_always), inline)]
+    fn mut_from_suffix_with_elems(
+        source: &mut [u8],
+        count: usize,
+    ) -> Result<(&mut [u8], &mut Self), CastError<&mut [u8], Self>>
+    where
+        Self: IntoBytes + KnownLayout<PointerMetadata = usize>,
+    {
+        mut_from_prefix_suffix(source, Some(count), CastType::Suffix).map(swap)
+    }
+
+    /// Reads a copy of `Self` from the given `source`.
+    ///
+    /// If `source.len() != size_of::<Self>()`, `read_from_bytes` returns `Err`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use zerocopy::FromBytes;
+    /// # use zerocopy_derive::*;
+    ///
+    /// #[derive(FromBytes)]
+    /// #[repr(C)]
+    /// struct PacketHeader {
+    ///     src_port: [u8; 2],
+    ///     dst_port: [u8; 2],
+    ///     length: [u8; 2],
+    ///     checksum: [u8; 2],
+    /// }
+    ///
+    /// // These bytes encode a `PacketHeader`.
+    /// let bytes = &[0, 1, 2, 3, 4, 5, 6, 7][..];
+    ///
+    /// let header = PacketHeader::read_from_bytes(bytes).unwrap();
+    ///
+    /// assert_eq!(header.src_port, [0, 1]);
+    /// assert_eq!(header.dst_port, [2, 3]);
+    /// assert_eq!(header.length, [4, 5]);
+    /// assert_eq!(header.checksum, [6, 7]);
+    /// ```
+    ///
+    #[doc = codegen_section!(
+        header = "h5",
+        bench = "read_from_bytes",
+        format = "coco_static_size",
+    )]
+    #[must_use = "has no side effects"]
+    #[cfg_attr(zerocopy_inline_always, inline(always))]
+    #[cfg_attr(not(zerocopy_inline_always), inline)]
+    fn read_from_bytes(source: &[u8]) -> Result<Self, SizeError<&[u8], Self>>
+    where
+        Self: Sized,
+    {
+        match Ref::<_, Unalign<Self>>::sized_from(source) {
+            Ok(r) => Ok(Ref::read(&r).into_inner()),
+            Err(CastError::Size(e)) => Err(e.with_dst()),
+            Err(CastError::Alignment(_)) => {
+                // SAFETY: `Unalign<Self>` is trivially aligned, so
+                // `Ref::sized_from` cannot fail due to unmet alignment
+                // requirements.
+                unsafe { core::hint::unreachable_unchecked() }
+            }
+            Err(CastError::Validity(i)) => match i {},
+        }
+    }
+
+    /// Reads a copy of `Self` from the prefix of the given `source`.
+    ///
+    /// This attempts to read a `Self` from the first `size_of::<Self>()` bytes
+    /// of `source`, returning that `Self` and any remaining bytes. If
+    /// `source.len() < size_of::<Self>()`, it returns `Err`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use zerocopy::FromBytes;
+    /// # use zerocopy_derive::*;
+    ///
+    /// #[derive(FromBytes)]
+    /// #[repr(C)]
+    /// struct PacketHeader {
+    ///     src_port: [u8; 2],
+    ///     dst_port: [u8; 2],
+    ///     length: [u8; 2],
+    ///     checksum: [u8; 2],
+    /// }
+    ///
+    /// // These are more bytes than are needed to encode a `PacketHeader`.
+    /// let bytes = &[0, 1, 2, 3, 4, 5, 6, 7, 8, 9][..];
+    ///
+    /// let (header, body) = PacketHeader::read_from_prefix(bytes).unwrap();
+    ///
+    /// assert_eq!(header.src_port, [0, 1]);
+    /// assert_eq!(header.dst_port, [2, 3]);
+    /// assert_eq!(header.length, [4, 5]);
+    /// assert_eq!(header.checksum, [6, 7]);
+    /// assert_eq!(body, [8, 9]);
+    /// ```
+    ///
+    #[doc = codegen_section!(
+        header = "h5",
+        bench = "read_from_prefix",
+        format = "coco_static_size",
+    )]
+    #[must_use = "has no side effects"]
+    #[cfg_attr(zerocopy_inline_always, inline(always))]
+    #[cfg_attr(not(zerocopy_inline_always), inline)]
+    fn read_from_prefix(source: &[u8]) -> Result<(Self, &[u8]), SizeError<&[u8], Self>>
+    where
+        Self: Sized,
+    {
+        match Ref::<_, Unalign<Self>>::sized_from_prefix(source) {
+            Ok((r, suffix)) => Ok((Ref::read(&r).into_inner(), suffix)),
+            Err(CastError::Size(e)) => Err(e.with_dst()),
+            Err(CastError::Alignment(_)) => {
+                // SAFETY: `Unalign<Self>` is trivially aligned, so
+                // `Ref::sized_from_prefix` cannot fail due to unmet alignment
+                // requirements.
+                unsafe { core::hint::unreachable_unchecked() }
+            }
+            Err(CastError::Validity(i)) => match i {},
+        }
+    }
+
+    /// Reads a copy of `Self` from the suffix of the given `source`.
+    ///
+    /// This attempts to read a `Self` from the last `size_of::<Self>()` bytes
+    /// of `source`, returning that `Self` and any preceding bytes. If
+    /// `source.len() < size_of::<Self>()`, it returns `Err`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use zerocopy::FromBytes;
+    /// # use zerocopy_derive::*;
+    ///
+    /// #[derive(FromBytes)]
+    /// #[repr(C)]
+    /// struct PacketTrailer {
+    ///     frame_check_sequence: [u8; 4],
+    /// }
+    ///
+    /// // These are more bytes than are needed to encode a `PacketTrailer`.
+    /// let bytes = &[0, 1, 2, 3, 4, 5, 6, 7, 8, 9][..];
+    ///
+    /// let (prefix, trailer) = PacketTrailer::read_from_suffix(bytes).unwrap();
+    ///
+    /// assert_eq!(prefix, [0, 1, 2, 3, 4, 5]);
+    /// assert_eq!(trailer.frame_check_sequence, [6, 7, 8, 9]);
+    /// ```
+    ///
+    #[doc = codegen_section!(
+        header = "h5",
+        bench = "read_from_suffix",
+        format = "coco_static_size",
+    )]
+    #[must_use = "has no side effects"]
+    #[cfg_attr(zerocopy_inline_always, inline(always))]
+    #[cfg_attr(not(zerocopy_inline_always), inline)]
+    fn read_from_suffix(source: &[u8]) -> Result<(&[u8], Self), SizeError<&[u8], Self>>
+    where
+        Self: Sized,
+    {
+        match Ref::<_, Unalign<Self>>::sized_from_suffix(source) {
+            Ok((prefix, r)) => Ok((prefix, Ref::read(&r).into_inner())),
+            Err(CastError::Size(e)) => Err(e.with_dst()),
+            Err(CastError::Alignment(_)) => {
+                // SAFETY: `Unalign<Self>` is trivially aligned, so
+                // `Ref::sized_from_suffix` cannot fail due to unmet alignment
+                // requirements.
+                unsafe { core::hint::unreachable_unchecked() }
+            }
+            Err(CastError::Validity(i)) => match i {},
+        }
+    }
+
+    /// Reads a copy of `self` from an `io::Read`.
+    ///
+    /// This is useful for interfacing with operating system byte sinks (files,
+    /// sockets, etc.).
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use zerocopy::{byteorder::big_endian::*, FromBytes};
+    /// use std::fs::File;
+    /// # use zerocopy_derive::*;
+    ///
+    /// #[derive(FromBytes)]
+    /// #[repr(C)]
+    /// struct BitmapFileHeader {
+    ///     signature: [u8; 2],
+    ///     size: U32,
+    ///     reserved: U64,
+    ///     offset: U64,
+    /// }
+    ///
+    /// let mut file = File::open("image.bin").unwrap();
+    /// let header = BitmapFileHeader::read_from_io(&mut file).unwrap();
+    /// ```
+    #[cfg(feature = "std")]
+    #[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
+    #[inline(always)]
+    fn read_from_io<R>(mut src: R) -> io::Result<Self>
+    where
+        Self: Sized,
+        R: io::Read,
+    {
+        // NOTE(#2319, #2320): We do `buf.zero()` separately rather than
+        // constructing `let buf = CoreMaybeUninit::zeroed()` because, if `Self`
+        // contains padding bytes, then a typed copy of `CoreMaybeUninit<Self>`
+        // will not necessarily preserve zeros written to those padding byte
+        // locations, and so `buf` could contain uninitialized bytes.
+        let mut buf = CoreMaybeUninit::<Self>::uninit();
+        buf.zero();
+
+        let ptr = Ptr::from_mut(&mut buf);
+        // SAFETY: After `buf.zero()`, `buf` consists entirely of initialized,
+        // zeroed bytes. Since `MaybeUninit` has no validity requirements, `ptr`
+        // cannot be used to write values which will violate `buf`'s bit
+        // validity. Since `ptr` has `Exclusive` aliasing, nothing other than
+        // `ptr` may be used to mutate `ptr`'s referent, and so its bit validity
+        // cannot be violated even though `buf` may have more permissive bit
+        // validity than `ptr`.
+        let ptr = unsafe { ptr.assume_validity::<invariant::Initialized>() };
+        let ptr = ptr.as_bytes();
+        src.read_exact(ptr.as_mut())?;
+        // SAFETY: `buf` entirely consists of initialized bytes, and `Self` is
+        // `FromBytes`.
+        Ok(unsafe { buf.assume_init() })
+    }
+
+    #[deprecated(since = "0.8.0", note = "renamed to `FromBytes::ref_from_bytes`")]
+    #[doc(hidden)]
+    #[must_use = "has no side effects"]
+    #[inline(always)]
+    fn ref_from(source: &[u8]) -> Option<&Self>
+    where
+        Self: KnownLayout + Immutable,
+    {
+        Self::ref_from_bytes(source).ok()
+    }
+
+    #[deprecated(since = "0.8.0", note = "renamed to `FromBytes::mut_from_bytes`")]
+    #[doc(hidden)]
+    #[must_use = "has no side effects"]
+    #[inline(always)]
+    fn mut_from(source: &mut [u8]) -> Option<&mut Self>
+    where
+        Self: KnownLayout + IntoBytes,
+    {
+        Self::mut_from_bytes(source).ok()
+    }
+
+    #[deprecated(since = "0.8.0", note = "renamed to `FromBytes::ref_from_prefix_with_elems`")]
+    #[doc(hidden)]
+    #[must_use = "has no side effects"]
+    #[inline(always)]
+    fn slice_from_prefix(source: &[u8], count: usize) -> Option<(&[Self], &[u8])>
+    where
+        Self: Sized + Immutable,
+    {
+        <[Self]>::ref_from_prefix_with_elems(source, count).ok()
+    }
+
+    #[deprecated(since = "0.8.0", note = "renamed to `FromBytes::ref_from_suffix_with_elems`")]
+    #[doc(hidden)]
+    #[must_use = "has no side effects"]
+    #[inline(always)]
+    fn slice_from_suffix(source: &[u8], count: usize) -> Option<(&[u8], &[Self])>
+    where
+        Self: Sized + Immutable,
+    {
+        <[Self]>::ref_from_suffix_with_elems(source, count).ok()
+    }
+
+    #[deprecated(since = "0.8.0", note = "renamed to `FromBytes::mut_from_prefix_with_elems`")]
+    #[doc(hidden)]
+    #[must_use = "has no side effects"]
+    #[inline(always)]
+    fn mut_slice_from_prefix(source: &mut [u8], count: usize) -> Option<(&mut [Self], &mut [u8])>
+    where
+        Self: Sized + IntoBytes,
+    {
+        <[Self]>::mut_from_prefix_with_elems(source, count).ok()
+    }
+
+    #[deprecated(since = "0.8.0", note = "renamed to `FromBytes::mut_from_suffix_with_elems`")]
+    #[doc(hidden)]
+    #[must_use = "has no side effects"]
+    #[inline(always)]
+    fn mut_slice_from_suffix(source: &mut [u8], count: usize) -> Option<(&mut [u8], &mut [Self])>
+    where
+        Self: Sized + IntoBytes,
+    {
+        <[Self]>::mut_from_suffix_with_elems(source, count).ok()
+    }
+
+    #[deprecated(since = "0.8.0", note = "renamed to `FromBytes::read_from_bytes`")]
+    #[doc(hidden)]
+    #[must_use = "has no side effects"]
+    #[inline(always)]
+    fn read_from(source: &[u8]) -> Option<Self>
+    where
+        Self: Sized,
+    {
+        Self::read_from_bytes(source).ok()
+    }
+}
+
+/// Interprets the given affix of the given bytes as a `&Self`.
+///
+/// This method computes the largest possible size of `Self` that can fit in the
+/// prefix or suffix bytes of `source`, then attempts to return both a reference
+/// to those bytes interpreted as a `Self`, and a reference to the excess bytes.
+/// If there are insufficient bytes, or if that affix of `source` is not
+/// appropriately aligned, this returns `Err`.
+#[inline(always)]
+fn ref_from_prefix_suffix<T: FromBytes + KnownLayout + Immutable + ?Sized>(
+    source: &[u8],
+    meta: Option<T::PointerMetadata>,
+    cast_type: CastType,
+) -> Result<(&T, &[u8]), CastError<&[u8], T>> {
+    let (slf, prefix_suffix) = Ptr::from_ref(source)
+        .try_cast_into::<_, BecauseImmutable>(cast_type, meta)
+        .map_err(|err| err.map_src(|s| s.as_ref()))?;
+    Ok((slf.recall_validity().as_ref(), prefix_suffix.as_ref()))
+}
+
+/// Interprets the given affix of the given bytes as a `&mut Self` without
+/// copying.
+///
+/// This method computes the largest possible size of `Self` that can fit in the
+/// prefix or suffix bytes of `source`, then attempts to return both a reference
+/// to those bytes interpreted as a `Self`, and a reference to the excess bytes.
+/// If there are insufficient bytes, or if that affix of `source` is not
+/// appropriately aligned, this returns `Err`.
+#[inline(always)]
+fn mut_from_prefix_suffix<T: FromBytes + IntoBytes + KnownLayout + ?Sized>(
+    source: &mut [u8],
+    meta: Option<T::PointerMetadata>,
+    cast_type: CastType,
+) -> Result<(&mut T, &mut [u8]), CastError<&mut [u8], T>> {
+    let (slf, prefix_suffix) = Ptr::from_mut(source)
+        .try_cast_into::<_, BecauseExclusive>(cast_type, meta)
+        .map_err(|err| err.map_src(|s| s.as_mut()))?;
+    Ok((slf.recall_validity::<_, (_, (_, _))>().as_mut(), prefix_suffix.as_mut()))
+}
+
+/// Analyzes whether a type is [`IntoBytes`].
+///
+/// This derive analyzes, at compile time, whether the annotated type satisfies
+/// the [safety conditions] of `IntoBytes` and implements `IntoBytes` if it is
+/// sound to do so. This derive can be applied to structs and enums (see below
+/// for union support); e.g.:
+///
+/// ```
+/// # use zerocopy_derive::{IntoBytes};
+/// #[derive(IntoBytes)]
+/// #[repr(C)]
+/// struct MyStruct {
+/// # /*
+///     ...
+/// # */
+/// }
+///
+/// #[derive(IntoBytes)]
+/// #[repr(u8)]
+/// enum MyEnum {
+/// #   Variant,
+/// # /*
+///     ...
+/// # */
+/// }
+/// ```
+///
+/// [safety conditions]: trait@IntoBytes#safety
+///
+/// # Error Messages
+///
+/// On Rust toolchains prior to 1.78.0, due to the way that the custom derive
+/// for `IntoBytes` is implemented, you may get an error like this:
+///
+/// ```text
+/// error[E0277]: the trait bound `(): PaddingFree<Foo, true>` is not satisfied
+///   --> lib.rs:23:10
+///    |
+///  1 | #[derive(IntoBytes)]
+///    |          ^^^^^^^^^ the trait `PaddingFree<Foo, true>` is not implemented for `()`
+///    |
+///    = help: the following implementations were found:
+///                   <() as PaddingFree<T, false>>
+/// ```
+///
+/// This error indicates that the type being annotated has padding bytes, which
+/// is illegal for `IntoBytes` types. Consider reducing the alignment of some
+/// fields by using types in the [`byteorder`] module, wrapping field types in
+/// [`Unalign`], adding explicit struct fields where those padding bytes would
+/// be, or using `#[repr(packed)]`. See the Rust Reference's page on [type
+/// layout] for more information about type layout and padding.
+///
+/// [type layout]: https://doc.rust-lang.org/reference/type-layout.html
+///
+/// # Unions
+///
+/// Currently, union bit validity is [up in the air][union-validity], and so
+/// zerocopy does not support `#[derive(IntoBytes)]` on unions by default.
+/// However, implementing `IntoBytes` on a union type is likely sound on all
+/// existing Rust toolchains - it's just that it may become unsound in the
+/// future. You can opt-in to `#[derive(IntoBytes)]` support on unions by
+/// passing the unstable `zerocopy_derive_union_into_bytes` cfg:
+///
+/// ```shell
+/// $ RUSTFLAGS='--cfg zerocopy_derive_union_into_bytes' cargo build
+/// ```
+///
+/// However, it is your responsibility to ensure that this derive is sound on
+/// the specific versions of the Rust toolchain you are using! We make no
+/// stability or soundness guarantees regarding this cfg, and may remove it at
+/// any point.
+///
+/// We are actively working with Rust to stabilize the necessary language
+/// guarantees to support this in a forwards-compatible way, which will enable
+/// us to remove the cfg gate. As part of this effort, we need to know how much
+/// demand there is for this feature. If you would like to use `IntoBytes` on
+/// unions, [please let us know][discussion].
+///
+/// [union-validity]: https://github.com/rust-lang/unsafe-code-guidelines/issues/438
+/// [discussion]: https://github.com/google/zerocopy/discussions/1802
+///
+/// # Analysis
+///
+/// *This section describes, roughly, the analysis performed by this derive to
+/// determine whether it is sound to implement `IntoBytes` for a given type.
+/// Unless you are modifying the implementation of this derive, or attempting to
+/// manually implement `IntoBytes` for a type yourself, you don't need to read
+/// this section.*
+///
+/// If a type has the following properties, then this derive can implement
+/// `IntoBytes` for that type:
+///
+/// - If the type is a struct, its fields must be [`IntoBytes`]. Additionally:
+///     - if the type is `repr(transparent)` or `repr(packed)`, it is
+///       [`IntoBytes`] if its fields are [`IntoBytes`]; else,
+///     - if the type is `repr(C)` with at most one field, it is [`IntoBytes`]
+///       if its field is [`IntoBytes`]; else,
+///     - if the type has no generic parameters, it is [`IntoBytes`] if the type
+///       is sized and has no padding bytes; else,
+///     - if the type is `repr(C)`, its fields must be [`Unaligned`].
+/// - If the type is an enum:
+///   - It must have a defined representation (`repr`s `C`, `u8`, `u16`, `u32`,
+///     `u64`, `usize`, `i8`, `i16`, `i32`, `i64`, or `isize`).
+///   - It must have no padding bytes.
+///   - Its fields must be [`IntoBytes`].
+///
+/// This analysis is subject to change. Unsafe code may *only* rely on the
+/// documented [safety conditions] of `FromBytes`, and must *not* rely on the
+/// implementation details of this derive.
+///
+/// [Rust Reference]: https://doc.rust-lang.org/reference/type-layout.html
+#[cfg(any(feature = "derive", test))]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "derive")))]
+pub use zerocopy_derive::IntoBytes;
+
+/// Types that can be converted to an immutable slice of initialized bytes.
+///
+/// Any `IntoBytes` type can be converted to a slice of initialized bytes of the
+/// same size. This is useful for efficiently serializing structured data as raw
+/// bytes.
+///
+/// # Implementation
+///
+/// **Do not implement this trait yourself!** Instead, use
+/// [`#[derive(IntoBytes)]`][derive]; e.g.:
+///
+/// ```
+/// # use zerocopy_derive::IntoBytes;
+/// #[derive(IntoBytes)]
+/// #[repr(C)]
+/// struct MyStruct {
+/// # /*
+///     ...
+/// # */
+/// }
+///
+/// #[derive(IntoBytes)]
+/// #[repr(u8)]
+/// enum MyEnum {
+/// #   Variant0,
+/// # /*
+///     ...
+/// # */
+/// }
+/// ```
+///
+/// This derive performs a sophisticated, compile-time safety analysis to
+/// determine whether a type is `IntoBytes`. See the [derive
+/// documentation][derive] for guidance on how to interpret error messages
+/// produced by the derive's analysis.
+///
+/// # Safety
+///
+/// *This section describes what is required in order for `T: IntoBytes`, and
+/// what unsafe code may assume of such types. If you don't plan on implementing
+/// `IntoBytes` manually, and you don't plan on writing unsafe code that
+/// operates on `IntoBytes` types, then you don't need to read this section.*
+///
+/// If `T: IntoBytes`, then unsafe code may assume that it is sound to treat any
+/// `t: T` as an immutable `[u8]` of length `size_of_val(t)`. If a type is
+/// marked as `IntoBytes` which violates this contract, it may cause undefined
+/// behavior.
+///
+/// `#[derive(IntoBytes)]` only permits [types which satisfy these
+/// requirements][derive-analysis].
+///
+#[cfg_attr(
+    feature = "derive",
+    doc = "[derive]: zerocopy_derive::IntoBytes",
+    doc = "[derive-analysis]: zerocopy_derive::IntoBytes#analysis"
+)]
+#[cfg_attr(
+    not(feature = "derive"),
+    doc = concat!("[derive]: https://docs.rs/zerocopy/", env!("CARGO_PKG_VERSION"), "/zerocopy/derive.IntoBytes.html"),
+    doc = concat!("[derive-analysis]: https://docs.rs/zerocopy/", env!("CARGO_PKG_VERSION"), "/zerocopy/derive.IntoBytes.html#analysis"),
+)]
+#[cfg_attr(
+    not(no_zerocopy_diagnostic_on_unimplemented_1_78_0),
+    diagnostic::on_unimplemented(note = "Consider adding `#[derive(IntoBytes)]` to `{Self}`")
+)]
+pub unsafe trait IntoBytes {
+    // The `Self: Sized` bound makes it so that this function doesn't prevent
+    // `IntoBytes` from being object safe. Note that other `IntoBytes` methods
+    // prevent object safety, but those provide a benefit in exchange for object
+    // safety. If at some point we remove those methods, change their type
+    // signatures, or move them out of this trait so that `IntoBytes` is object
+    // safe again, it's important that this function not prevent object safety.
+    #[doc(hidden)]
+    fn only_derive_is_allowed_to_implement_this_trait()
+    where
+        Self: Sized;
+
+    /// Gets the bytes of this value.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use zerocopy::IntoBytes;
+    /// # use zerocopy_derive::*;
+    ///
+    /// #[derive(IntoBytes, Immutable)]
+    /// #[repr(C)]
+    /// struct PacketHeader {
+    ///     src_port: [u8; 2],
+    ///     dst_port: [u8; 2],
+    ///     length: [u8; 2],
+    ///     checksum: [u8; 2],
+    /// }
+    ///
+    /// let header = PacketHeader {
+    ///     src_port: [0, 1],
+    ///     dst_port: [2, 3],
+    ///     length: [4, 5],
+    ///     checksum: [6, 7],
+    /// };
+    ///
+    /// let bytes = header.as_bytes();
+    ///
+    /// assert_eq!(bytes, [0, 1, 2, 3, 4, 5, 6, 7]);
+    /// ```
+    ///
+    #[doc = codegen_section!(
+        header = "h5",
+        bench = "as_bytes",
+        format = "coco",
+        arity = 2,
+        [
+            open
+            @index 1
+            @title "Sized"
+            @variant "static_size"
+        ],
+        [
+            @index 2
+            @title "Unsized"
+            @variant "dynamic_size"
+        ]
+    )]
+    #[must_use = "has no side effects"]
+    #[inline(always)]
+    fn as_bytes(&self) -> &[u8]
+    where
+        Self: Immutable,
+    {
+        // Note that this method does not have a `Self: Sized` bound;
+        // `size_of_val` works for unsized values too.
+        let len = mem::size_of_val(self);
+        let slf: *const Self = self;
+
+        // SAFETY:
+        // - `slf.cast::<u8>()` is valid for reads for `len * size_of::<u8>()`
+        //   many bytes because...
+        //   - `slf` is the same pointer as `self`, and `self` is a reference
+        //     which points to an object whose size is `len`. Thus...
+        //     - The entire region of `len` bytes starting at `slf` is contained
+        //       within a single allocation.
+        //     - `slf` is non-null.
+        //   - `slf` is trivially aligned to `align_of::<u8>() == 1`.
+        // - `Self: IntoBytes` ensures that all of the bytes of `slf` are
+        //   initialized.
+        // - Since `slf` is derived from `self`, and `self` is an immutable
+        //   reference, the only other references to this memory region that
+        //   could exist are other immutable references, which by `Self:
+        //   Immutable` don't permit mutation.
+        // - The total size of the resulting slice is no larger than
+        //   `isize::MAX` because no allocation produced by safe code can be
+        //   larger than `isize::MAX`.
+        //
+        // FIXME(#429): Add references to docs and quotes.
+        unsafe { slice::from_raw_parts(slf.cast::<u8>(), len) }
+    }
+
+    /// Gets the bytes of this value mutably.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use zerocopy::IntoBytes;
+    /// # use zerocopy_derive::*;
+    ///
+    /// # #[derive(Eq, PartialEq, Debug)]
+    /// #[derive(FromBytes, IntoBytes, Immutable)]
+    /// #[repr(C)]
+    /// struct PacketHeader {
+    ///     src_port: [u8; 2],
+    ///     dst_port: [u8; 2],
+    ///     length: [u8; 2],
+    ///     checksum: [u8; 2],
+    /// }
+    ///
+    /// let mut header = PacketHeader {
+    ///     src_port: [0, 1],
+    ///     dst_port: [2, 3],
+    ///     length: [4, 5],
+    ///     checksum: [6, 7],
+    /// };
+    ///
+    /// let bytes = header.as_mut_bytes();
+    ///
+    /// assert_eq!(bytes, [0, 1, 2, 3, 4, 5, 6, 7]);
+    ///
+    /// bytes.reverse();
+    ///
+    /// assert_eq!(header, PacketHeader {
+    ///     src_port: [7, 6],
+    ///     dst_port: [5, 4],
+    ///     length: [3, 2],
+    ///     checksum: [1, 0],
+    /// });
+    /// ```
+    ///
+    #[doc = codegen_header!("h5", "as_mut_bytes")]
+    ///
+    /// See [`IntoBytes::as_bytes`](#method.as_bytes.codegen).
+    #[must_use = "has no side effects"]
+    #[inline(always)]
+    fn as_mut_bytes(&mut self) -> &mut [u8]
+    where
+        Self: FromBytes,
+    {
+        // Note that this method does not have a `Self: Sized` bound;
+        // `size_of_val` works for unsized values too.
+        let len = mem::size_of_val(self);
+        let slf: *mut Self = self;
+
+        // SAFETY:
+        // - `slf.cast::<u8>()` is valid for reads and writes for `len *
+        //   size_of::<u8>()` many bytes because...
+        //   - `slf` is the same pointer as `self`, and `self` is a reference
+        //     which points to an object whose size is `len`. Thus...
+        //     - The entire region of `len` bytes starting at `slf` is contained
+        //       within a single allocation.
+        //     - `slf` is non-null.
+        //   - `slf` is trivially aligned to `align_of::<u8>() == 1`.
+        // - `Self: IntoBytes` ensures that all of the bytes of `slf` are
+        //   initialized.
+        // - `Self: FromBytes` ensures that no write to this memory region
+        //   could result in it containing an invalid `Self`.
+        // - Since `slf` is derived from `self`, and `self` is a mutable
+        //   reference, no other references to this memory region can exist.
+        // - The total size of the resulting slice is no larger than
+        //   `isize::MAX` because no allocation produced by safe code can be
+        //   larger than `isize::MAX`.
+        //
+        // FIXME(#429): Add references to docs and quotes.
+        unsafe { slice::from_raw_parts_mut(slf.cast::<u8>(), len) }
+    }
+
+    /// Writes a copy of `self` to `dst`.
+    ///
+    /// If `dst.len() != size_of_val(self)`, `write_to` returns `Err`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use zerocopy::IntoBytes;
+    /// # use zerocopy_derive::*;
+    ///
+    /// #[derive(IntoBytes, Immutable)]
+    /// #[repr(C)]
+    /// struct PacketHeader {
+    ///     src_port: [u8; 2],
+    ///     dst_port: [u8; 2],
+    ///     length: [u8; 2],
+    ///     checksum: [u8; 2],
+    /// }
+    ///
+    /// let header = PacketHeader {
+    ///     src_port: [0, 1],
+    ///     dst_port: [2, 3],
+    ///     length: [4, 5],
+    ///     checksum: [6, 7],
+    /// };
+    ///
+    /// let mut bytes = [0, 0, 0, 0, 0, 0, 0, 0];
+    ///
+    /// header.write_to(&mut bytes[..]);
+    ///
+    /// assert_eq!(bytes, [0, 1, 2, 3, 4, 5, 6, 7]);
+    /// ```
+    ///
+    /// If too many or too few target bytes are provided, `write_to` returns
+    /// `Err` and leaves the target bytes unmodified:
+    ///
+    /// ```
+    /// # use zerocopy::IntoBytes;
+    /// # let header = u128::MAX;
+    /// let mut excessive_bytes = &mut [0u8; 128][..];
+    ///
+    /// let write_result = header.write_to(excessive_bytes);
+    ///
+    /// assert!(write_result.is_err());
+    /// assert_eq!(excessive_bytes, [0u8; 128]);
+    /// ```
+    ///
+    #[doc = codegen_section!(
+        header = "h5",
+        bench = "write_to",
+        format = "coco",
+        arity = 2,
+        [
+            open
+            @index 1
+            @title "Sized"
+            @variant "static_size"
+        ],
+        [
+            @index 2
+            @title "Unsized"
+            @variant "dynamic_size"
+        ]
+    )]
+    #[must_use = "callers should check the return value to see if the operation succeeded"]
+    #[cfg_attr(zerocopy_inline_always, inline(always))]
+    #[cfg_attr(not(zerocopy_inline_always), inline)]
+    #[allow(clippy::mut_from_ref)] // False positive: `&self -> &mut [u8]`
+    fn write_to(&self, dst: &mut [u8]) -> Result<(), SizeError<&Self, &mut [u8]>>
+    where
+        Self: Immutable,
+    {
+        let src = self.as_bytes();
+        if dst.len() == src.len() {
+            // SAFETY: Within this branch of the conditional, we have ensured
+            // that `dst.len()` is equal to `src.len()`. Neither the size of the
+            // source nor the size of the destination change between the above
+            // size check and the invocation of `copy_unchecked`.
+            unsafe { util::copy_unchecked(src, dst) }
+            Ok(())
+        } else {
+            Err(SizeError::new(self))
+        }
+    }
+
+    /// Writes a copy of `self` to the prefix of `dst`.
+    ///
+    /// `write_to_prefix` writes `self` to the first `size_of_val(self)` bytes
+    /// of `dst`. If `dst.len() < size_of_val(self)`, it returns `Err`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use zerocopy::IntoBytes;
+    /// # use zerocopy_derive::*;
+    ///
+    /// #[derive(IntoBytes, Immutable)]
+    /// #[repr(C)]
+    /// struct PacketHeader {
+    ///     src_port: [u8; 2],
+    ///     dst_port: [u8; 2],
+    ///     length: [u8; 2],
+    ///     checksum: [u8; 2],
+    /// }
+    ///
+    /// let header = PacketHeader {
+    ///     src_port: [0, 1],
+    ///     dst_port: [2, 3],
+    ///     length: [4, 5],
+    ///     checksum: [6, 7],
+    /// };
+    ///
+    /// let mut bytes = [0, 0, 0, 0, 0, 0, 0, 0, 0, 0];
+    ///
+    /// header.write_to_prefix(&mut bytes[..]);
+    ///
+    /// assert_eq!(bytes, [0, 1, 2, 3, 4, 5, 6, 7, 0, 0]);
+    /// ```
+    ///
+    /// If insufficient target bytes are provided, `write_to_prefix` returns
+    /// `Err` and leaves the target bytes unmodified:
+    ///
+    /// ```
+    /// # use zerocopy::IntoBytes;
+    /// # let header = u128::MAX;
+    /// let mut insufficient_bytes = &mut [0, 0][..];
+    ///
+    /// let write_result = header.write_to_suffix(insufficient_bytes);
+    ///
+    /// assert!(write_result.is_err());
+    /// assert_eq!(insufficient_bytes, [0, 0]);
+    /// ```
+    ///
+    #[doc = codegen_section!(
+        header = "h5",
+        bench = "write_to_prefix",
+        format = "coco",
+        arity = 2,
+        [
+            open
+            @index 1
+            @title "Sized"
+            @variant "static_size"
+        ],
+        [
+            @index 2
+            @title "Unsized"
+            @variant "dynamic_size"
+        ]
+    )]
+    #[must_use = "callers should check the return value to see if the operation succeeded"]
+    #[cfg_attr(zerocopy_inline_always, inline(always))]
+    #[cfg_attr(not(zerocopy_inline_always), inline)]
+    #[allow(clippy::mut_from_ref)] // False positive: `&self -> &mut [u8]`
+    fn write_to_prefix(&self, dst: &mut [u8]) -> Result<(), SizeError<&Self, &mut [u8]>>
+    where
+        Self: Immutable,
+    {
+        let src = self.as_bytes();
+        match dst.get_mut(..src.len()) {
+            Some(dst) => {
+                // SAFETY: Within this branch of the `match`, we have ensured
+                // through fallible subslicing that `dst.len()` is equal to
+                // `src.len()`. Neither the size of the source nor the size of
+                // the destination change between the above subslicing operation
+                // and the invocation of `copy_unchecked`.
+                unsafe { util::copy_unchecked(src, dst) }
+                Ok(())
+            }
+            None => Err(SizeError::new(self)),
+        }
+    }
+
+    /// Writes a copy of `self` to the suffix of `dst`.
+    ///
+    /// `write_to_suffix` writes `self` to the last `size_of_val(self)` bytes of
+    /// `dst`. If `dst.len() < size_of_val(self)`, it returns `Err`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use zerocopy::IntoBytes;
+    /// # use zerocopy_derive::*;
+    ///
+    /// #[derive(IntoBytes, Immutable)]
+    /// #[repr(C)]
+    /// struct PacketHeader {
+    ///     src_port: [u8; 2],
+    ///     dst_port: [u8; 2],
+    ///     length: [u8; 2],
+    ///     checksum: [u8; 2],
+    /// }
+    ///
+    /// let header = PacketHeader {
+    ///     src_port: [0, 1],
+    ///     dst_port: [2, 3],
+    ///     length: [4, 5],
+    ///     checksum: [6, 7],
+    /// };
+    ///
+    /// let mut bytes = [0, 0, 0, 0, 0, 0, 0, 0, 0, 0];
+    ///
+    /// header.write_to_suffix(&mut bytes[..]);
+    ///
+    /// assert_eq!(bytes, [0, 0, 0, 1, 2, 3, 4, 5, 6, 7]);
+    ///
+    /// let mut insufficient_bytes = &mut [0, 0][..];
+    ///
+    /// let write_result = header.write_to_suffix(insufficient_bytes);
+    ///
+    /// assert!(write_result.is_err());
+    /// assert_eq!(insufficient_bytes, [0, 0]);
+    /// ```
+    ///
+    /// If insufficient target bytes are provided, `write_to_suffix` returns
+    /// `Err` and leaves the target bytes unmodified:
+    ///
+    /// ```
+    /// # use zerocopy::IntoBytes;
+    /// # let header = u128::MAX;
+    /// let mut insufficient_bytes = &mut [0, 0][..];
+    ///
+    /// let write_result = header.write_to_suffix(insufficient_bytes);
+    ///
+    /// assert!(write_result.is_err());
+    /// assert_eq!(insufficient_bytes, [0, 0]);
+    /// ```
+    ///
+    #[doc = codegen_section!(
+        header = "h5",
+        bench = "write_to_suffix",
+        format = "coco",
+        arity = 2,
+        [
+            open
+            @index 1
+            @title "Sized"
+            @variant "static_size"
+        ],
+        [
+            @index 2
+            @title "Unsized"
+            @variant "dynamic_size"
+        ]
+    )]
+    #[must_use = "callers should check the return value to see if the operation succeeded"]
+    #[cfg_attr(zerocopy_inline_always, inline(always))]
+    #[cfg_attr(not(zerocopy_inline_always), inline)]
+    #[allow(clippy::mut_from_ref)] // False positive: `&self -> &mut [u8]`
+    fn write_to_suffix(&self, dst: &mut [u8]) -> Result<(), SizeError<&Self, &mut [u8]>>
+    where
+        Self: Immutable,
+    {
+        let src = self.as_bytes();
+        let start = if let Some(start) = dst.len().checked_sub(src.len()) {
+            start
+        } else {
+            return Err(SizeError::new(self));
+        };
+        let dst = if let Some(dst) = dst.get_mut(start..) {
+            dst
+        } else {
+            // get_mut() should never return None here. We return a `SizeError`
+            // rather than .unwrap() because in the event the branch is not
+            // optimized away, returning a value is generally lighter-weight
+            // than panicking.
+            return Err(SizeError::new(self));
+        };
+        // SAFETY: Through fallible subslicing of `dst`, we have ensured that
+        // `dst.len()` is equal to `src.len()`. Neither the size of the source
+        // nor the size of the destination change between the above subslicing
+        // operation and the invocation of `copy_unchecked`.
+        unsafe {
+            util::copy_unchecked(src, dst);
+        }
+        Ok(())
+    }
+
+    /// Writes a copy of `self` to an `io::Write`.
+    ///
+    /// This is a shorthand for `dst.write_all(self.as_bytes())`, and is useful
+    /// for interfacing with operating system byte sinks (files, sockets, etc.).
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use zerocopy::{byteorder::big_endian::U16, FromBytes, IntoBytes};
+    /// use std::fs::File;
+    /// # use zerocopy_derive::*;
+    ///
+    /// #[derive(FromBytes, IntoBytes, Immutable, KnownLayout)]
+    /// #[repr(C, packed)]
+    /// struct GrayscaleImage {
+    ///     height: U16,
+    ///     width: U16,
+    ///     pixels: [U16],
+    /// }
+    ///
+    /// let image = GrayscaleImage::ref_from_bytes(&[0, 0, 0, 0][..]).unwrap();
+    /// let mut file = File::create("image.bin").unwrap();
+    /// image.write_to_io(&mut file).unwrap();
+    /// ```
+    ///
+    /// If the write fails, `write_to_io` returns `Err` and a partial write may
+    /// have occurred; e.g.:
+    ///
+    /// ```
+    /// # use zerocopy::IntoBytes;
+    ///
+    /// let src = u128::MAX;
+    /// let mut dst = [0u8; 2];
+    ///
+    /// let write_result = src.write_to_io(&mut dst[..]);
+    ///
+    /// assert!(write_result.is_err());
+    /// assert_eq!(dst, [255, 255]);
+    /// ```
+    #[cfg(feature = "std")]
+    #[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
+    #[inline(always)]
+    fn write_to_io<W>(&self, mut dst: W) -> io::Result<()>
+    where
+        Self: Immutable,
+        W: io::Write,
+    {
+        dst.write_all(self.as_bytes())
+    }
+
+    #[deprecated(since = "0.8.0", note = "`IntoBytes::as_bytes_mut` was renamed to `as_mut_bytes`")]
+    #[doc(hidden)]
+    #[inline]
+    fn as_bytes_mut(&mut self) -> &mut [u8]
+    where
+        Self: FromBytes,
+    {
+        self.as_mut_bytes()
+    }
+}
+
+/// Analyzes whether a type is [`Unaligned`].
+///
+/// This derive analyzes, at compile time, whether the annotated type satisfies
+/// the [safety conditions] of `Unaligned` and implements `Unaligned` if it is
+/// sound to do so. This derive can be applied to structs, enums, and unions;
+/// e.g.:
+///
+/// ```
+/// # use zerocopy_derive::Unaligned;
+/// #[derive(Unaligned)]
+/// #[repr(C)]
+/// struct MyStruct {
+/// # /*
+///     ...
+/// # */
+/// }
+///
+/// #[derive(Unaligned)]
+/// #[repr(u8)]
+/// enum MyEnum {
+/// #   Variant0,
+/// # /*
+///     ...
+/// # */
+/// }
+///
+/// #[derive(Unaligned)]
+/// #[repr(packed)]
+/// union MyUnion {
+/// #   variant: u8,
+/// # /*
+///     ...
+/// # */
+/// }
+/// ```
+///
+/// # Analysis
+///
+/// *This section describes, roughly, the analysis performed by this derive to
+/// determine whether it is sound to implement `Unaligned` for a given type.
+/// Unless you are modifying the implementation of this derive, or attempting to
+/// manually implement `Unaligned` for a type yourself, you don't need to read
+/// this section.*
+///
+/// If a type has the following properties, then this derive can implement
+/// `Unaligned` for that type:
+///
+/// - If the type is a struct or union:
+///   - If `repr(align(N))` is provided, `N` must equal 1.
+///   - If the type is `repr(C)` or `repr(transparent)`, all fields must be
+///     [`Unaligned`].
+///   - If the type is not `repr(C)` or `repr(transparent)`, it must be
+///     `repr(packed)` or `repr(packed(1))`.
+/// - If the type is an enum:
+///   - If `repr(align(N))` is provided, `N` must equal 1.
+///   - It must be a field-less enum (meaning that all variants have no fields).
+///   - It must be `repr(i8)` or `repr(u8)`.
+///
+/// [safety conditions]: trait@Unaligned#safety
+#[cfg(any(feature = "derive", test))]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "derive")))]
+pub use zerocopy_derive::Unaligned;
+
+/// Types with no alignment requirement.
+///
+/// If `T: Unaligned`, then `align_of::<T>() == 1`.
+///
+/// # Implementation
+///
+/// **Do not implement this trait yourself!** Instead, use
+/// [`#[derive(Unaligned)]`][derive]; e.g.:
+///
+/// ```
+/// # use zerocopy_derive::Unaligned;
+/// #[derive(Unaligned)]
+/// #[repr(C)]
+/// struct MyStruct {
+/// # /*
+///     ...
+/// # */
+/// }
+///
+/// #[derive(Unaligned)]
+/// #[repr(u8)]
+/// enum MyEnum {
+/// #   Variant0,
+/// # /*
+///     ...
+/// # */
+/// }
+///
+/// #[derive(Unaligned)]
+/// #[repr(packed)]
+/// union MyUnion {
+/// #   variant: u8,
+/// # /*
+///     ...
+/// # */
+/// }
+/// ```
+///
+/// This derive performs a sophisticated, compile-time safety analysis to
+/// determine whether a type is `Unaligned`.
+///
+/// # Safety
+///
+/// *This section describes what is required in order for `T: Unaligned`, and
+/// what unsafe code may assume of such types. If you don't plan on implementing
+/// `Unaligned` manually, and you don't plan on writing unsafe code that
+/// operates on `Unaligned` types, then you don't need to read this section.*
+///
+/// If `T: Unaligned`, then unsafe code may assume that it is sound to produce a
+/// reference to `T` at any memory location regardless of alignment. If a type
+/// is marked as `Unaligned` which violates this contract, it may cause
+/// undefined behavior.
+///
+/// `#[derive(Unaligned)]` only permits [types which satisfy these
+/// requirements][derive-analysis].
+///
+#[cfg_attr(
+    feature = "derive",
+    doc = "[derive]: zerocopy_derive::Unaligned",
+    doc = "[derive-analysis]: zerocopy_derive::Unaligned#analysis"
+)]
+#[cfg_attr(
+    not(feature = "derive"),
+    doc = concat!("[derive]: https://docs.rs/zerocopy/", env!("CARGO_PKG_VERSION"), "/zerocopy/derive.Unaligned.html"),
+    doc = concat!("[derive-analysis]: https://docs.rs/zerocopy/", env!("CARGO_PKG_VERSION"), "/zerocopy/derive.Unaligned.html#analysis"),
+)]
+#[cfg_attr(
+    not(no_zerocopy_diagnostic_on_unimplemented_1_78_0),
+    diagnostic::on_unimplemented(note = "Consider adding `#[derive(Unaligned)]` to `{Self}`")
+)]
+pub unsafe trait Unaligned {
+    // The `Self: Sized` bound makes it so that `Unaligned` is still object
+    // safe.
+    #[doc(hidden)]
+    fn only_derive_is_allowed_to_implement_this_trait()
+    where
+        Self: Sized;
+}
+
+/// Derives optimized [`PartialEq`] and [`Eq`] implementations.
+///
+/// This derive can be applied to structs and enums implementing both
+/// [`Immutable`] and [`IntoBytes`]; e.g.:
+///
+/// ```
+/// # use zerocopy_derive::{ByteEq, Immutable, IntoBytes};
+/// #[derive(ByteEq, Immutable, IntoBytes)]
+/// #[repr(C)]
+/// struct MyStruct {
+/// # /*
+///     ...
+/// # */
+/// }
+///
+/// #[derive(ByteEq, Immutable, IntoBytes)]
+/// #[repr(u8)]
+/// enum MyEnum {
+/// #   Variant,
+/// # /*
+///     ...
+/// # */
+/// }
+/// ```
+///
+/// The standard library's [`derive(Eq, PartialEq)`][derive@PartialEq] computes
+/// equality by individually comparing each field. Instead, the implementation
+/// of [`PartialEq::eq`] emitted by `derive(ByteHash)` converts the entirety of
+/// `self` and `other` to byte slices and compares those slices for equality.
+/// This may have performance advantages.
+#[cfg(any(feature = "derive", test))]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "derive")))]
+pub use zerocopy_derive::ByteEq;
+/// Derives an optimized [`Hash`] implementation.
+///
+/// This derive can be applied to structs and enums implementing both
+/// [`Immutable`] and [`IntoBytes`]; e.g.:
+///
+/// ```
+/// # use zerocopy_derive::{ByteHash, Immutable, IntoBytes};
+/// #[derive(ByteHash, Immutable, IntoBytes)]
+/// #[repr(C)]
+/// struct MyStruct {
+/// # /*
+///     ...
+/// # */
+/// }
+///
+/// #[derive(ByteHash, Immutable, IntoBytes)]
+/// #[repr(u8)]
+/// enum MyEnum {
+/// #   Variant,
+/// # /*
+///     ...
+/// # */
+/// }
+/// ```
+///
+/// The standard library's [`derive(Hash)`][derive@Hash] produces hashes by
+/// individually hashing each field and combining the results. Instead, the
+/// implementations of [`Hash::hash()`] and [`Hash::hash_slice()`] generated by
+/// `derive(ByteHash)` convert the entirety of `self` to a byte slice and hashes
+/// it in a single call to [`Hasher::write()`]. This may have performance
+/// advantages.
+///
+/// [`Hash`]: core::hash::Hash
+/// [`Hash::hash()`]: core::hash::Hash::hash()
+/// [`Hash::hash_slice()`]: core::hash::Hash::hash_slice()
+#[cfg(any(feature = "derive", test))]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "derive")))]
+pub use zerocopy_derive::ByteHash;
+/// Implements [`SplitAt`].
+///
+/// This derive can be applied to structs; e.g.:
+///
+/// ```
+/// # use zerocopy_derive::{ByteEq, Immutable, IntoBytes};
+/// #[derive(ByteEq, Immutable, IntoBytes)]
+/// #[repr(C)]
+/// struct MyStruct {
+/// # /*
+///     ...
+/// # */
+/// }
+/// ```
+#[cfg(any(feature = "derive", test))]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "derive")))]
+pub use zerocopy_derive::SplitAt;
+
+#[cfg(feature = "alloc")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "alloc")))]
+#[cfg(not(no_zerocopy_panic_in_const_and_vec_try_reserve_1_57_0))]
+mod alloc_support {
+    use super::*;
+
+    /// Extends a `Vec<T>` by pushing `additional` new items onto the end of the
+    /// vector. The new items are initialized with zeros.
+    #[cfg(not(no_zerocopy_panic_in_const_and_vec_try_reserve_1_57_0))]
+    #[doc(hidden)]
+    #[deprecated(since = "0.8.0", note = "moved to `FromZeros`")]
+    #[inline(always)]
+    pub fn extend_vec_zeroed<T: FromZeros>(
+        v: &mut Vec<T>,
+        additional: usize,
+    ) -> Result<(), AllocError> {
+        <T as FromZeros>::extend_vec_zeroed(v, additional)
+    }
+
+    /// Inserts `additional` new items into `Vec<T>` at `position`. The new
+    /// items are initialized with zeros.
+    ///
+    /// # Panics
+    ///
+    /// Panics if `position > v.len()`.
+    #[cfg(not(no_zerocopy_panic_in_const_and_vec_try_reserve_1_57_0))]
+    #[doc(hidden)]
+    #[deprecated(since = "0.8.0", note = "moved to `FromZeros`")]
+    #[inline(always)]
+    pub fn insert_vec_zeroed<T: FromZeros>(
+        v: &mut Vec<T>,
+        position: usize,
+        additional: usize,
+    ) -> Result<(), AllocError> {
+        <T as FromZeros>::insert_vec_zeroed(v, position, additional)
+    }
+}
+
+#[cfg(feature = "alloc")]
+#[cfg(not(no_zerocopy_panic_in_const_and_vec_try_reserve_1_57_0))]
+#[doc(hidden)]
+pub use alloc_support::*;
+
+#[cfg(test)]
+#[allow(clippy::assertions_on_result_states, clippy::unreadable_literal)]
+mod tests {
+    use static_assertions::assert_impl_all;
+
+    use super::*;
+    use crate::util::testutil::*;
+
+    // An unsized type.
+    //
+    // This is used to test the custom derives of our traits. The `[u8]` type
+    // gets a hand-rolled impl, so it doesn't exercise our custom derives.
+    #[derive(Debug, Eq, PartialEq, FromBytes, IntoBytes, Unaligned, Immutable)]
+    #[repr(transparent)]
+    struct Unsized([u8]);
+
+    impl Unsized {
+        fn from_mut_slice(slc: &mut [u8]) -> &mut Unsized {
+            // SAFETY: This *probably* sound - since the layouts of `[u8]` and
+            // `Unsized` are the same, so are the layouts of `&mut [u8]` and
+            // `&mut Unsized`. [1] Even if it turns out that this isn't actually
+            // guaranteed by the language spec, we can just change this since
+            // it's in test code.
+            //
+            // [1] https://github.com/rust-lang/unsafe-code-guidelines/issues/375
+            unsafe { mem::transmute(slc) }
+        }
+    }
+
+    #[test]
+    fn test_known_layout() {
+        // Test that `$ty` and `ManuallyDrop<$ty>` have the expected layout.
+        // Test that `PhantomData<$ty>` has the same layout as `()` regardless
+        // of `$ty`.
+        macro_rules! test {
+            ($ty:ty, $expect:expr) => {
+                let expect = $expect;
+                assert_eq!(<$ty as KnownLayout>::LAYOUT, expect);
+                assert_eq!(<ManuallyDrop<$ty> as KnownLayout>::LAYOUT, expect);
+                assert_eq!(<PhantomData<$ty> as KnownLayout>::LAYOUT, <() as KnownLayout>::LAYOUT);
+            };
+        }
+
+        let layout =
+            |offset, align, trailing_slice_elem_size, statically_shallow_unpadded| DstLayout {
+                align: NonZeroUsize::new(align).unwrap(),
+                size_info: match trailing_slice_elem_size {
+                    None => SizeInfo::Sized { size: offset },
+                    Some(elem_size) => {
+                        SizeInfo::SliceDst(TrailingSliceLayout { offset, elem_size })
+                    }
+                },
+                statically_shallow_unpadded,
+            };
+
+        test!((), layout(0, 1, None, false));
+        test!(u8, layout(1, 1, None, false));
+        // Use `align_of` because `u64` alignment may be smaller than 8 on some
+        // platforms.
+        test!(u64, layout(8, mem::align_of::<u64>(), None, false));
+        test!(AU64, layout(8, 8, None, false));
+
+        test!(Option<&'static ()>, usize::LAYOUT);
+
+        test!([()], layout(0, 1, Some(0), true));
+        test!([u8], layout(0, 1, Some(1), true));
+        test!(str, layout(0, 1, Some(1), true));
+    }
+
+    #[cfg(feature = "derive")]
+    #[test]
+    fn test_known_layout_derive() {
+        // In this and other files (`late_compile_pass.rs`,
+        // `mid_compile_pass.rs`, and `struct.rs`), we test success and failure
+        // modes of `derive(KnownLayout)` for the following combination of
+        // properties:
+        //
+        // +------------+--------------------------------------+-----------+
+        // |            |      trailing field properties       |           |
+        // | `repr(C)`? | generic? | `KnownLayout`? | `Sized`? | Type Name |
+        // |------------+----------+----------------+----------+-----------|
+        // |          N |        N |              N |        N |      KL00 |
+        // |          N |        N |              N |        Y |      KL01 |
+        // |          N |        N |              Y |        N |      KL02 |
+        // |          N |        N |              Y |        Y |      KL03 |
+        // |          N |        Y |              N |        N |      KL04 |
+        // |          N |        Y |              N |        Y |      KL05 |
+        // |          N |        Y |              Y |        N |      KL06 |
+        // |          N |        Y |              Y |        Y |      KL07 |
+        // |          Y |        N |              N |        N |      KL08 |
+        // |          Y |        N |              N |        Y |      KL09 |
+        // |          Y |        N |              Y |        N |      KL10 |
+        // |          Y |        N |              Y |        Y |      KL11 |
+        // |          Y |        Y |              N |        N |      KL12 |
+        // |          Y |        Y |              N |        Y |      KL13 |
+        // |          Y |        Y |              Y |        N |      KL14 |
+        // |          Y |        Y |              Y |        Y |      KL15 |
+        // +------------+----------+----------------+----------+-----------+
+
+        struct NotKnownLayout<T = ()> {
+            _t: T,
+        }
+
+        #[derive(KnownLayout)]
+        #[repr(C)]
+        struct AlignSize<const ALIGN: usize, const SIZE: usize>
+        where
+            elain::Align<ALIGN>: elain::Alignment,
+        {
+            _align: elain::Align<ALIGN>,
+            size: [u8; SIZE],
+        }
+
+        type AU16 = AlignSize<2, 2>;
+        type AU32 = AlignSize<4, 4>;
+
+        fn _assert_kl<T: ?Sized + KnownLayout>(_: &T) {}
+
+        let sized_layout = |align, size| DstLayout {
+            align: NonZeroUsize::new(align).unwrap(),
+            size_info: SizeInfo::Sized { size },
+            statically_shallow_unpadded: false,
+        };
+
+        let unsized_layout = |align, elem_size, offset, statically_shallow_unpadded| DstLayout {
+            align: NonZeroUsize::new(align).unwrap(),
+            size_info: SizeInfo::SliceDst(TrailingSliceLayout { offset, elem_size }),
+            statically_shallow_unpadded,
+        };
+
+        // | `repr(C)`? | generic? | `KnownLayout`? | `Sized`? | Type Name |
+        // |          N |        N |              N |        Y |      KL01 |
+        #[allow(dead_code)]
+        #[derive(KnownLayout)]
+        struct KL01(NotKnownLayout<AU32>, NotKnownLayout<AU16>);
+
+        let expected = DstLayout::for_type::<KL01>();
+
+        assert_eq!(<KL01 as KnownLayout>::LAYOUT, expected);
+        assert_eq!(<KL01 as KnownLayout>::LAYOUT, sized_layout(4, 8));
+
+        // ...with `align(N)`:
+        #[allow(dead_code)]
+        #[derive(KnownLayout)]
+        #[repr(align(64))]
+        struct KL01Align(NotKnownLayout<AU32>, NotKnownLayout<AU16>);
+
+        let expected = DstLayout::for_type::<KL01Align>();
+
+        assert_eq!(<KL01Align as KnownLayout>::LAYOUT, expected);
+        assert_eq!(<KL01Align as KnownLayout>::LAYOUT, sized_layout(64, 64));
+
+        // ...with `packed`:
+        #[allow(dead_code)]
+        #[derive(KnownLayout)]
+        #[repr(packed)]
+        struct KL01Packed(NotKnownLayout<AU32>, NotKnownLayout<AU16>);
+
+        let expected = DstLayout::for_type::<KL01Packed>();
+
+        assert_eq!(<KL01Packed as KnownLayout>::LAYOUT, expected);
+        assert_eq!(<KL01Packed as KnownLayout>::LAYOUT, sized_layout(1, 6));
+
+        // ...with `packed(N)`:
+        #[allow(dead_code)]
+        #[derive(KnownLayout)]
+        #[repr(packed(2))]
+        struct KL01PackedN(NotKnownLayout<AU32>, NotKnownLayout<AU16>);
+
+        assert_impl_all!(KL01PackedN: KnownLayout);
+
+        let expected = DstLayout::for_type::<KL01PackedN>();
+
+        assert_eq!(<KL01PackedN as KnownLayout>::LAYOUT, expected);
+        assert_eq!(<KL01PackedN as KnownLayout>::LAYOUT, sized_layout(2, 6));
+
+        // | `repr(C)`? | generic? | `KnownLayout`? | `Sized`? | Type Name |
+        // |          N |        N |              Y |        Y |      KL03 |
+        #[allow(dead_code)]
+        #[derive(KnownLayout)]
+        struct KL03(NotKnownLayout, u8);
+
+        let expected = DstLayout::for_type::<KL03>();
+
+        assert_eq!(<KL03 as KnownLayout>::LAYOUT, expected);
+        assert_eq!(<KL03 as KnownLayout>::LAYOUT, sized_layout(1, 1));
+
+        // ... with `align(N)`
+        #[allow(dead_code)]
+        #[derive(KnownLayout)]
+        #[repr(align(64))]
+        struct KL03Align(NotKnownLayout<AU32>, u8);
+
+        let expected = DstLayout::for_type::<KL03Align>();
+
+        assert_eq!(<KL03Align as KnownLayout>::LAYOUT, expected);
+        assert_eq!(<KL03Align as KnownLayout>::LAYOUT, sized_layout(64, 64));
+
+        // ... with `packed`:
+        #[allow(dead_code)]
+        #[derive(KnownLayout)]
+        #[repr(packed)]
+        struct KL03Packed(NotKnownLayout<AU32>, u8);
+
+        let expected = DstLayout::for_type::<KL03Packed>();
+
+        assert_eq!(<KL03Packed as KnownLayout>::LAYOUT, expected);
+        assert_eq!(<KL03Packed as KnownLayout>::LAYOUT, sized_layout(1, 5));
+
+        // ... with `packed(N)`
+        #[allow(dead_code)]
+        #[derive(KnownLayout)]
+        #[repr(packed(2))]
+        struct KL03PackedN(NotKnownLayout<AU32>, u8);
+
+        assert_impl_all!(KL03PackedN: KnownLayout);
+
+        let expected = DstLayout::for_type::<KL03PackedN>();
+
+        assert_eq!(<KL03PackedN as KnownLayout>::LAYOUT, expected);
+        assert_eq!(<KL03PackedN as KnownLayout>::LAYOUT, sized_layout(2, 6));
+
+        // | `repr(C)`? | generic? | `KnownLayout`? | `Sized`? | Type Name |
+        // |          N |        Y |              N |        Y |      KL05 |
+        #[allow(dead_code)]
+        #[derive(KnownLayout)]
+        struct KL05<T>(u8, T);
+
+        fn _test_kl05<T>(t: T) -> impl KnownLayout {
+            KL05(0u8, t)
+        }
+
+        // | `repr(C)`? | generic? | `KnownLayout`? | `Sized`? | Type Name |
+        // |          N |        Y |              Y |        Y |      KL07 |
+        #[allow(dead_code)]
+        #[derive(KnownLayout)]
+        struct KL07<T: KnownLayout>(u8, T);
+
+        fn _test_kl07<T: KnownLayout>(t: T) -> impl KnownLayout {
+            let _ = KL07(0u8, t);
+        }
+
+        // | `repr(C)`? | generic? | `KnownLayout`? | `Sized`? | Type Name |
+        // |          Y |        N |              Y |        N |      KL10 |
+        #[allow(dead_code)]
+        #[derive(KnownLayout)]
+        #[repr(C)]
+        struct KL10(NotKnownLayout<AU32>, [u8]);
+
+        let expected = DstLayout::new_zst(None)
+            .extend(DstLayout::for_type::<NotKnownLayout<AU32>>(), None)
+            .extend(<[u8] as KnownLayout>::LAYOUT, None)
+            .pad_to_align();
+
+        assert_eq!(<KL10 as KnownLayout>::LAYOUT, expected);
+        assert_eq!(<KL10 as KnownLayout>::LAYOUT, unsized_layout(4, 1, 4, false));
+
+        // ...with `align(N)`:
+        #[allow(dead_code)]
+        #[derive(KnownLayout)]
+        #[repr(C, align(64))]
+        struct KL10Align(NotKnownLayout<AU32>, [u8]);
+
+        let repr_align = NonZeroUsize::new(64);
+
+        let expected = DstLayout::new_zst(repr_align)
+            .extend(DstLayout::for_type::<NotKnownLayout<AU32>>(), None)
+            .extend(<[u8] as KnownLayout>::LAYOUT, None)
+            .pad_to_align();
+
+        assert_eq!(<KL10Align as KnownLayout>::LAYOUT, expected);
+        assert_eq!(<KL10Align as KnownLayout>::LAYOUT, unsized_layout(64, 1, 4, false));
+
+        // ...with `packed`:
+        #[allow(dead_code)]
+        #[derive(KnownLayout)]
+        #[repr(C, packed)]
+        struct KL10Packed(NotKnownLayout<AU32>, [u8]);
+
+        let repr_packed = NonZeroUsize::new(1);
+
+        let expected = DstLayout::new_zst(None)
+            .extend(DstLayout::for_type::<NotKnownLayout<AU32>>(), repr_packed)
+            .extend(<[u8] as KnownLayout>::LAYOUT, repr_packed)
+            .pad_to_align();
+
+        assert_eq!(<KL10Packed as KnownLayout>::LAYOUT, expected);
+        assert_eq!(<KL10Packed as KnownLayout>::LAYOUT, unsized_layout(1, 1, 4, false));
+
+        // ...with `packed(N)`:
+        #[allow(dead_code)]
+        #[derive(KnownLayout)]
+        #[repr(C, packed(2))]
+        struct KL10PackedN(NotKnownLayout<AU32>, [u8]);
+
+        let repr_packed = NonZeroUsize::new(2);
+
+        let expected = DstLayout::new_zst(None)
+            .extend(DstLayout::for_type::<NotKnownLayout<AU32>>(), repr_packed)
+            .extend(<[u8] as KnownLayout>::LAYOUT, repr_packed)
+            .pad_to_align();
+
+        assert_eq!(<KL10PackedN as KnownLayout>::LAYOUT, expected);
+        assert_eq!(<KL10PackedN as KnownLayout>::LAYOUT, unsized_layout(2, 1, 4, false));
+
+        // | `repr(C)`? | generic? | `KnownLayout`? | `Sized`? | Type Name |
+        // |          Y |        N |              Y |        Y |      KL11 |
+        #[allow(dead_code)]
+        #[derive(KnownLayout)]
+        #[repr(C)]
+        struct KL11(NotKnownLayout<AU64>, u8);
+
+        let expected = DstLayout::new_zst(None)
+            .extend(DstLayout::for_type::<NotKnownLayout<AU64>>(), None)
+            .extend(<u8 as KnownLayout>::LAYOUT, None)
+            .pad_to_align();
+
+        assert_eq!(<KL11 as KnownLayout>::LAYOUT, expected);
+        assert_eq!(<KL11 as KnownLayout>::LAYOUT, sized_layout(8, 16));
+
+        // ...with `align(N)`:
+        #[allow(dead_code)]
+        #[derive(KnownLayout)]
+        #[repr(C, align(64))]
+        struct KL11Align(NotKnownLayout<AU64>, u8);
+
+        let repr_align = NonZeroUsize::new(64);
+
+        let expected = DstLayout::new_zst(repr_align)
+            .extend(DstLayout::for_type::<NotKnownLayout<AU64>>(), None)
+            .extend(<u8 as KnownLayout>::LAYOUT, None)
+            .pad_to_align();
+
+        assert_eq!(<KL11Align as KnownLayout>::LAYOUT, expected);
+        assert_eq!(<KL11Align as KnownLayout>::LAYOUT, sized_layout(64, 64));
+
+        // ...with `packed`:
+        #[allow(dead_code)]
+        #[derive(KnownLayout)]
+        #[repr(C, packed)]
+        struct KL11Packed(NotKnownLayout<AU64>, u8);
+
+        let repr_packed = NonZeroUsize::new(1);
+
+        let expected = DstLayout::new_zst(None)
+            .extend(DstLayout::for_type::<NotKnownLayout<AU64>>(), repr_packed)
+            .extend(<u8 as KnownLayout>::LAYOUT, repr_packed)
+            .pad_to_align();
+
+        assert_eq!(<KL11Packed as KnownLayout>::LAYOUT, expected);
+        assert_eq!(<KL11Packed as KnownLayout>::LAYOUT, sized_layout(1, 9));
+
+        // ...with `packed(N)`:
+        #[allow(dead_code)]
+        #[derive(KnownLayout)]
+        #[repr(C, packed(2))]
+        struct KL11PackedN(NotKnownLayout<AU64>, u8);
+
+        let repr_packed = NonZeroUsize::new(2);
+
+        let expected = DstLayout::new_zst(None)
+            .extend(DstLayout::for_type::<NotKnownLayout<AU64>>(), repr_packed)
+            .extend(<u8 as KnownLayout>::LAYOUT, repr_packed)
+            .pad_to_align();
+
+        assert_eq!(<KL11PackedN as KnownLayout>::LAYOUT, expected);
+        assert_eq!(<KL11PackedN as KnownLayout>::LAYOUT, sized_layout(2, 10));
+
+        // | `repr(C)`? | generic? | `KnownLayout`? | `Sized`? | Type Name |
+        // |          Y |        Y |              Y |        N |      KL14 |
+        #[allow(dead_code)]
+        #[derive(KnownLayout)]
+        #[repr(C)]
+        struct KL14<T: ?Sized + KnownLayout>(u8, T);
+
+        fn _test_kl14<T: ?Sized + KnownLayout>(kl: &KL14<T>) {
+            _assert_kl(kl)
+        }
+
+        // | `repr(C)`? | generic? | `KnownLayout`? | `Sized`? | Type Name |
+        // |          Y |        Y |              Y |        Y |      KL15 |
+        #[allow(dead_code)]
+        #[derive(KnownLayout)]
+        #[repr(C)]
+        struct KL15<T: KnownLayout>(u8, T);
+
+        fn _test_kl15<T: KnownLayout>(t: T) -> impl KnownLayout {
+            let _ = KL15(0u8, t);
+        }
+
+        // Test a variety of combinations of field types:
+        //  - ()
+        //  - u8
+        //  - AU16
+        //  - [()]
+        //  - [u8]
+        //  - [AU16]
+
+        #[allow(clippy::upper_case_acronyms, dead_code)]
+        #[derive(KnownLayout)]
+        #[repr(C)]
+        struct KLTU<T, U: ?Sized>(T, U);
+
+        assert_eq!(<KLTU<(), ()> as KnownLayout>::LAYOUT, sized_layout(1, 0));
+
+        assert_eq!(<KLTU<(), u8> as KnownLayout>::LAYOUT, sized_layout(1, 1));
+
+        assert_eq!(<KLTU<(), AU16> as KnownLayout>::LAYOUT, sized_layout(2, 2));
+
+        assert_eq!(<KLTU<(), [()]> as KnownLayout>::LAYOUT, unsized_layout(1, 0, 0, false));
+
+        assert_eq!(<KLTU<(), [u8]> as KnownLayout>::LAYOUT, unsized_layout(1, 1, 0, false));
+
+        assert_eq!(<KLTU<(), [AU16]> as KnownLayout>::LAYOUT, unsized_layout(2, 2, 0, false));
+
+        assert_eq!(<KLTU<u8, ()> as KnownLayout>::LAYOUT, sized_layout(1, 1));
+
+        assert_eq!(<KLTU<u8, u8> as KnownLayout>::LAYOUT, sized_layout(1, 2));
+
+        assert_eq!(<KLTU<u8, AU16> as KnownLayout>::LAYOUT, sized_layout(2, 4));
+
+        assert_eq!(<KLTU<u8, [()]> as KnownLayout>::LAYOUT, unsized_layout(1, 0, 1, false));
+
+        assert_eq!(<KLTU<u8, [u8]> as KnownLayout>::LAYOUT, unsized_layout(1, 1, 1, false));
+
+        assert_eq!(<KLTU<u8, [AU16]> as KnownLayout>::LAYOUT, unsized_layout(2, 2, 2, false));
+
+        assert_eq!(<KLTU<AU16, ()> as KnownLayout>::LAYOUT, sized_layout(2, 2));
+
+        assert_eq!(<KLTU<AU16, u8> as KnownLayout>::LAYOUT, sized_layout(2, 4));
+
+        assert_eq!(<KLTU<AU16, AU16> as KnownLayout>::LAYOUT, sized_layout(2, 4));
+
+        assert_eq!(<KLTU<AU16, [()]> as KnownLayout>::LAYOUT, unsized_layout(2, 0, 2, false));
+
+        assert_eq!(<KLTU<AU16, [u8]> as KnownLayout>::LAYOUT, unsized_layout(2, 1, 2, false));
+
+        assert_eq!(<KLTU<AU16, [AU16]> as KnownLayout>::LAYOUT, unsized_layout(2, 2, 2, false));
+
+        // Test a variety of field counts.
+
+        #[derive(KnownLayout)]
+        #[repr(C)]
+        struct KLF0;
+
+        assert_eq!(<KLF0 as KnownLayout>::LAYOUT, sized_layout(1, 0));
+
+        #[derive(KnownLayout)]
+        #[repr(C)]
+        struct KLF1([u8]);
+
+        assert_eq!(<KLF1 as KnownLayout>::LAYOUT, unsized_layout(1, 1, 0, true));
+
+        #[derive(KnownLayout)]
+        #[repr(C)]
+        struct KLF2(NotKnownLayout<u8>, [u8]);
+
+        assert_eq!(<KLF2 as KnownLayout>::LAYOUT, unsized_layout(1, 1, 1, false));
+
+        #[derive(KnownLayout)]
+        #[repr(C)]
+        struct KLF3(NotKnownLayout<u8>, NotKnownLayout<AU16>, [u8]);
+
+        assert_eq!(<KLF3 as KnownLayout>::LAYOUT, unsized_layout(2, 1, 4, false));
+
+        #[derive(KnownLayout)]
+        #[repr(C)]
+        struct KLF4(NotKnownLayout<u8>, NotKnownLayout<AU16>, NotKnownLayout<AU32>, [u8]);
+
+        assert_eq!(<KLF4 as KnownLayout>::LAYOUT, unsized_layout(4, 1, 8, false));
+    }
+
+    #[test]
+    fn test_object_safety() {
+        fn _takes_immutable(_: &dyn Immutable) {}
+        fn _takes_unaligned(_: &dyn Unaligned) {}
+    }
+
+    #[test]
+    fn test_from_zeros_only() {
+        // Test types that implement `FromZeros` but not `FromBytes`.
+
+        assert!(!bool::new_zeroed());
+        assert_eq!(char::new_zeroed(), '\0');
+
+        #[cfg(feature = "alloc")]
+        {
+            assert_eq!(bool::new_box_zeroed(), Ok(Box::new(false)));
+            assert_eq!(char::new_box_zeroed(), Ok(Box::new('\0')));
+
+            assert_eq!(
+                <[bool]>::new_box_zeroed_with_elems(3).unwrap().as_ref(),
+                [false, false, false]
+            );
+            assert_eq!(
+                <[char]>::new_box_zeroed_with_elems(3).unwrap().as_ref(),
+                ['\0', '\0', '\0']
+            );
+
+            assert_eq!(bool::new_vec_zeroed(3).unwrap().as_ref(), [false, false, false]);
+            assert_eq!(char::new_vec_zeroed(3).unwrap().as_ref(), ['\0', '\0', '\0']);
+        }
+
+        let mut string = "hello".to_string();
+        let s: &mut str = string.as_mut();
+        assert_eq!(s, "hello");
+        s.zero();
+        assert_eq!(s, "\0\0\0\0\0");
+    }
+
+    #[test]
+    fn test_zst_count_preserved() {
+        // Test that, when an explicit count is provided to for a type with a
+        // ZST trailing slice element, that count is preserved. This is
+        // important since, for such types, all element counts result in objects
+        // of the same size, and so the correct behavior is ambiguous. However,
+        // preserving the count as requested by the user is the behavior that we
+        // document publicly.
+
+        // FromZeros methods
+        #[cfg(feature = "alloc")]
+        assert_eq!(<[()]>::new_box_zeroed_with_elems(3).unwrap().len(), 3);
+        #[cfg(feature = "alloc")]
+        assert_eq!(<()>::new_vec_zeroed(3).unwrap().len(), 3);
+
+        // FromBytes methods
+        assert_eq!(<[()]>::ref_from_bytes_with_elems(&[][..], 3).unwrap().len(), 3);
+        assert_eq!(<[()]>::ref_from_prefix_with_elems(&[][..], 3).unwrap().0.len(), 3);
+        assert_eq!(<[()]>::ref_from_suffix_with_elems(&[][..], 3).unwrap().1.len(), 3);
+        assert_eq!(<[()]>::mut_from_bytes_with_elems(&mut [][..], 3).unwrap().len(), 3);
+        assert_eq!(<[()]>::mut_from_prefix_with_elems(&mut [][..], 3).unwrap().0.len(), 3);
+        assert_eq!(<[()]>::mut_from_suffix_with_elems(&mut [][..], 3).unwrap().1.len(), 3);
+    }
+
+    #[test]
+    fn test_read_write() {
+        const VAL: u64 = 0x12345678;
+        #[cfg(target_endian = "big")]
+        const VAL_BYTES: [u8; 8] = VAL.to_be_bytes();
+        #[cfg(target_endian = "little")]
+        const VAL_BYTES: [u8; 8] = VAL.to_le_bytes();
+        const ZEROS: [u8; 8] = [0u8; 8];
+
+        // Test `FromBytes::{read_from, read_from_prefix, read_from_suffix}`.
+
+        assert_eq!(u64::read_from_bytes(&VAL_BYTES[..]), Ok(VAL));
+        // The first 8 bytes are from `VAL_BYTES` and the second 8 bytes are all
+        // zeros.
+        let bytes_with_prefix: [u8; 16] = transmute!([VAL_BYTES, [0; 8]]);
+        assert_eq!(u64::read_from_prefix(&bytes_with_prefix[..]), Ok((VAL, &ZEROS[..])));
+        assert_eq!(u64::read_from_suffix(&bytes_with_prefix[..]), Ok((&VAL_BYTES[..], 0)));
+        // The first 8 bytes are all zeros and the second 8 bytes are from
+        // `VAL_BYTES`
+        let bytes_with_suffix: [u8; 16] = transmute!([[0; 8], VAL_BYTES]);
+        assert_eq!(u64::read_from_prefix(&bytes_with_suffix[..]), Ok((0, &VAL_BYTES[..])));
+        assert_eq!(u64::read_from_suffix(&bytes_with_suffix[..]), Ok((&ZEROS[..], VAL)));
+
+        // Test `IntoBytes::{write_to, write_to_prefix, write_to_suffix}`.
+
+        let mut bytes = [0u8; 8];
+        assert_eq!(VAL.write_to(&mut bytes[..]), Ok(()));
+        assert_eq!(bytes, VAL_BYTES);
+        let mut bytes = [0u8; 16];
+        assert_eq!(VAL.write_to_prefix(&mut bytes[..]), Ok(()));
+        let want: [u8; 16] = transmute!([VAL_BYTES, [0; 8]]);
+        assert_eq!(bytes, want);
+        let mut bytes = [0u8; 16];
+        assert_eq!(VAL.write_to_suffix(&mut bytes[..]), Ok(()));
+        let want: [u8; 16] = transmute!([[0; 8], VAL_BYTES]);
+        assert_eq!(bytes, want);
+    }
+
+    #[test]
+    #[cfg(feature = "std")]
+    fn test_read_io_with_padding_soundness() {
+        // This test is designed to exhibit potential UB in
+        // `FromBytes::read_from_io`. (see #2319, #2320).
+
+        // On most platforms (where `align_of::<u16>() == 2`), `WithPadding`
+        // will have inter-field padding between `x` and `y`.
+        #[derive(FromBytes)]
+        #[repr(C)]
+        struct WithPadding {
+            x: u8,
+            y: u16,
+        }
+        struct ReadsInRead;
+        impl std::io::Read for ReadsInRead {
+            fn read(&mut self, buf: &mut [u8]) -> std::io::Result<usize> {
+                // This body branches on every byte of `buf`, ensuring that it
+                // exhibits UB if any byte of `buf` is uninitialized.
+                if buf.iter().all(|&x| x == 0) {
+                    Ok(buf.len())
+                } else {
+                    buf.iter_mut().for_each(|x| *x = 0);
+                    Ok(buf.len())
+                }
+            }
+        }
+        assert!(matches!(WithPadding::read_from_io(ReadsInRead), Ok(WithPadding { x: 0, y: 0 })));
+    }
+
+    #[test]
+    #[cfg(feature = "std")]
+    fn test_read_write_io() {
+        let mut long_buffer = [0, 0, 0, 0];
+        assert!(matches!(u16::MAX.write_to_io(&mut long_buffer[..]), Ok(())));
+        assert_eq!(long_buffer, [255, 255, 0, 0]);
+        assert!(matches!(u16::read_from_io(&long_buffer[..]), Ok(u16::MAX)));
+
+        let mut short_buffer = [0, 0];
+        assert!(u32::MAX.write_to_io(&mut short_buffer[..]).is_err());
+        assert_eq!(short_buffer, [255, 255]);
+        assert!(u32::read_from_io(&short_buffer[..]).is_err());
+    }
+
+    #[test]
+    fn test_try_from_bytes_try_read_from() {
+        assert_eq!(<bool as TryFromBytes>::try_read_from_bytes(&[0]), Ok(false));
+        assert_eq!(<bool as TryFromBytes>::try_read_from_bytes(&[1]), Ok(true));
+
+        assert_eq!(<bool as TryFromBytes>::try_read_from_prefix(&[0, 2]), Ok((false, &[2][..])));
+        assert_eq!(<bool as TryFromBytes>::try_read_from_prefix(&[1, 2]), Ok((true, &[2][..])));
+
+        assert_eq!(<bool as TryFromBytes>::try_read_from_suffix(&[2, 0]), Ok((&[2][..], false)));
+        assert_eq!(<bool as TryFromBytes>::try_read_from_suffix(&[2, 1]), Ok((&[2][..], true)));
+
+        // If we don't pass enough bytes, it fails.
+        assert!(matches!(
+            <u8 as TryFromBytes>::try_read_from_bytes(&[]),
+            Err(TryReadError::Size(_))
+        ));
+        assert!(matches!(
+            <u8 as TryFromBytes>::try_read_from_prefix(&[]),
+            Err(TryReadError::Size(_))
+        ));
+        assert!(matches!(
+            <u8 as TryFromBytes>::try_read_from_suffix(&[]),
+            Err(TryReadError::Size(_))
+        ));
+
+        // If we pass too many bytes, it fails.
+        assert!(matches!(
+            <u8 as TryFromBytes>::try_read_from_bytes(&[0, 0]),
+            Err(TryReadError::Size(_))
+        ));
+
+        // If we pass an invalid value, it fails.
+        assert!(matches!(
+            <bool as TryFromBytes>::try_read_from_bytes(&[2]),
+            Err(TryReadError::Validity(_))
+        ));
+        assert!(matches!(
+            <bool as TryFromBytes>::try_read_from_prefix(&[2, 0]),
+            Err(TryReadError::Validity(_))
+        ));
+        assert!(matches!(
+            <bool as TryFromBytes>::try_read_from_suffix(&[0, 2]),
+            Err(TryReadError::Validity(_))
+        ));
+
+        // Reading from a misaligned buffer should still succeed. Since `AU64`'s
+        // alignment is 8, and since we read from two adjacent addresses one
+        // byte apart, it is guaranteed that at least one of them (though
+        // possibly both) will be misaligned.
+        let bytes: [u8; 9] = [0, 0, 0, 0, 0, 0, 0, 0, 0];
+        assert_eq!(<AU64 as TryFromBytes>::try_read_from_bytes(&bytes[..8]), Ok(AU64(0)));
+        assert_eq!(<AU64 as TryFromBytes>::try_read_from_bytes(&bytes[1..9]), Ok(AU64(0)));
+
+        assert_eq!(
+            <AU64 as TryFromBytes>::try_read_from_prefix(&bytes[..8]),
+            Ok((AU64(0), &[][..]))
+        );
+        assert_eq!(
+            <AU64 as TryFromBytes>::try_read_from_prefix(&bytes[1..9]),
+            Ok((AU64(0), &[][..]))
+        );
+
+        assert_eq!(
+            <AU64 as TryFromBytes>::try_read_from_suffix(&bytes[..8]),
+            Ok((&[][..], AU64(0)))
+        );
+        assert_eq!(
+            <AU64 as TryFromBytes>::try_read_from_suffix(&bytes[1..9]),
+            Ok((&[][..], AU64(0)))
+        );
+    }
+
+    #[test]
+    fn test_ref_from_mut_from_bytes() {
+        // Test `FromBytes::{ref_from_bytes, mut_from_bytes}{,_prefix,Suffix}`
+        // success cases. Exhaustive coverage for these methods is covered by
+        // the `Ref` tests above, which these helper methods defer to.
+
+        let mut buf =
+            Align::<[u8; 16], AU64>::new([0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15]);
+
+        assert_eq!(
+            AU64::ref_from_bytes(&buf.t[8..]).unwrap().0.to_ne_bytes(),
+            [8, 9, 10, 11, 12, 13, 14, 15]
+        );
+        let suffix = AU64::mut_from_bytes(&mut buf.t[8..]).unwrap();
+        suffix.0 = 0x0101010101010101;
+        // The `[u8:9]` is a non-half size of the full buffer, which would catch
+        // `from_prefix` having the same implementation as `from_suffix` (issues #506, #511).
+        assert_eq!(
+            <[u8; 9]>::ref_from_suffix(&buf.t[..]).unwrap(),
+            (&[0, 1, 2, 3, 4, 5, 6][..], &[7u8, 1, 1, 1, 1, 1, 1, 1, 1])
+        );
+        let (prefix, suffix) = AU64::mut_from_suffix(&mut buf.t[1..]).unwrap();
+        assert_eq!(prefix, &mut [1u8, 2, 3, 4, 5, 6, 7][..]);
+        suffix.0 = 0x0202020202020202;
+        let (prefix, suffix) = <[u8; 10]>::mut_from_suffix(&mut buf.t[..]).unwrap();
+        assert_eq!(prefix, &mut [0u8, 1, 2, 3, 4, 5][..]);
+        suffix[0] = 42;
+        assert_eq!(
+            <[u8; 9]>::ref_from_prefix(&buf.t[..]).unwrap(),
+            (&[0u8, 1, 2, 3, 4, 5, 42, 7, 2], &[2u8, 2, 2, 2, 2, 2, 2][..])
+        );
+        <[u8; 2]>::mut_from_prefix(&mut buf.t[..]).unwrap().0[1] = 30;
+        assert_eq!(buf.t, [0, 30, 2, 3, 4, 5, 42, 7, 2, 2, 2, 2, 2, 2, 2, 2]);
+    }
+
+    #[test]
+    fn test_ref_from_mut_from_bytes_error() {
+        // Test `FromBytes::{ref_from_bytes, mut_from_bytes}{,_prefix,Suffix}`
+        // error cases.
+
+        // Fail because the buffer is too large.
+        let mut buf = Align::<[u8; 16], AU64>::default();
+        // `buf.t` should be aligned to 8, so only the length check should fail.
+        assert!(AU64::ref_from_bytes(&buf.t[..]).is_err());
+        assert!(AU64::mut_from_bytes(&mut buf.t[..]).is_err());
+        assert!(<[u8; 8]>::ref_from_bytes(&buf.t[..]).is_err());
+        assert!(<[u8; 8]>::mut_from_bytes(&mut buf.t[..]).is_err());
+
+        // Fail because the buffer is too small.
+        let mut buf = Align::<[u8; 4], AU64>::default();
+        assert!(AU64::ref_from_bytes(&buf.t[..]).is_err());
+        assert!(AU64::mut_from_bytes(&mut buf.t[..]).is_err());
+        assert!(<[u8; 8]>::ref_from_bytes(&buf.t[..]).is_err());
+        assert!(<[u8; 8]>::mut_from_bytes(&mut buf.t[..]).is_err());
+        assert!(AU64::ref_from_prefix(&buf.t[..]).is_err());
+        assert!(AU64::mut_from_prefix(&mut buf.t[..]).is_err());
+        assert!(AU64::ref_from_suffix(&buf.t[..]).is_err());
+        assert!(AU64::mut_from_suffix(&mut buf.t[..]).is_err());
+        assert!(<[u8; 8]>::ref_from_prefix(&buf.t[..]).is_err());
+        assert!(<[u8; 8]>::mut_from_prefix(&mut buf.t[..]).is_err());
+        assert!(<[u8; 8]>::ref_from_suffix(&buf.t[..]).is_err());
+        assert!(<[u8; 8]>::mut_from_suffix(&mut buf.t[..]).is_err());
+
+        // Fail because the alignment is insufficient.
+        let mut buf = Align::<[u8; 13], AU64>::default();
+        assert!(AU64::ref_from_bytes(&buf.t[1..]).is_err());
+        assert!(AU64::mut_from_bytes(&mut buf.t[1..]).is_err());
+        assert!(AU64::ref_from_bytes(&buf.t[1..]).is_err());
+        assert!(AU64::mut_from_bytes(&mut buf.t[1..]).is_err());
+        assert!(AU64::ref_from_prefix(&buf.t[1..]).is_err());
+        assert!(AU64::mut_from_prefix(&mut buf.t[1..]).is_err());
+        assert!(AU64::ref_from_suffix(&buf.t[..]).is_err());
+        assert!(AU64::mut_from_suffix(&mut buf.t[..]).is_err());
+    }
+
+    #[test]
+    fn test_to_methods() {
+        /// Run a series of tests by calling `IntoBytes` methods on `t`.
+        ///
+        /// `bytes` is the expected byte sequence returned from `t.as_bytes()`
+        /// before `t` has been modified. `post_mutation` is the expected
+        /// sequence returned from `t.as_bytes()` after `t.as_mut_bytes()[0]`
+        /// has had its bits flipped (by applying `^= 0xFF`).
+        ///
+        /// `N` is the size of `t` in bytes.
+        fn test<T: FromBytes + IntoBytes + Immutable + Debug + Eq + ?Sized, const N: usize>(
+            t: &mut T,
+            bytes: &[u8],
+            post_mutation: &T,
+        ) {
+            // Test that we can access the underlying bytes, and that we get the
+            // right bytes and the right number of bytes.
+            assert_eq!(t.as_bytes(), bytes);
+
+            // Test that changes to the underlying byte slices are reflected in
+            // the original object.
+            t.as_mut_bytes()[0] ^= 0xFF;
+            assert_eq!(t, post_mutation);
+            t.as_mut_bytes()[0] ^= 0xFF;
+
+            // `write_to` rejects slices that are too small or too large.
+            assert!(t.write_to(&mut vec![0; N - 1][..]).is_err());
+            assert!(t.write_to(&mut vec![0; N + 1][..]).is_err());
+
+            // `write_to` works as expected.
+            let mut bytes = [0; N];
+            assert_eq!(t.write_to(&mut bytes[..]), Ok(()));
+            assert_eq!(bytes, t.as_bytes());
+
+            // `write_to_prefix` rejects slices that are too small.
+            assert!(t.write_to_prefix(&mut vec![0; N - 1][..]).is_err());
+
+            // `write_to_prefix` works with exact-sized slices.
+            let mut bytes = [0; N];
+            assert_eq!(t.write_to_prefix(&mut bytes[..]), Ok(()));
+            assert_eq!(bytes, t.as_bytes());
+
+            // `write_to_prefix` works with too-large slices, and any bytes past
+            // the prefix aren't modified.
+            let mut too_many_bytes = vec![0; N + 1];
+            too_many_bytes[N] = 123;
+            assert_eq!(t.write_to_prefix(&mut too_many_bytes[..]), Ok(()));
+            assert_eq!(&too_many_bytes[..N], t.as_bytes());
+            assert_eq!(too_many_bytes[N], 123);
+
+            // `write_to_suffix` rejects slices that are too small.
+            assert!(t.write_to_suffix(&mut vec![0; N - 1][..]).is_err());
+
+            // `write_to_suffix` works with exact-sized slices.
+            let mut bytes = [0; N];
+            assert_eq!(t.write_to_suffix(&mut bytes[..]), Ok(()));
+            assert_eq!(bytes, t.as_bytes());
+
+            // `write_to_suffix` works with too-large slices, and any bytes
+            // before the suffix aren't modified.
+            let mut too_many_bytes = vec![0; N + 1];
+            too_many_bytes[0] = 123;
+            assert_eq!(t.write_to_suffix(&mut too_many_bytes[..]), Ok(()));
+            assert_eq!(&too_many_bytes[1..], t.as_bytes());
+            assert_eq!(too_many_bytes[0], 123);
+        }
+
+        #[derive(Debug, Eq, PartialEq, FromBytes, IntoBytes, Immutable)]
+        #[repr(C)]
+        struct Foo {
+            a: u32,
+            b: Wrapping<u32>,
+            c: Option<NonZeroU32>,
+        }
+
+        let expected_bytes: Vec<u8> = if cfg!(target_endian = "little") {
+            vec![1, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0]
+        } else {
+            vec![0, 0, 0, 1, 0, 0, 0, 2, 0, 0, 0, 0]
+        };
+        let post_mutation_expected_a =
+            if cfg!(target_endian = "little") { 0x00_00_00_FE } else { 0xFF_00_00_01 };
+        test::<_, 12>(
+            &mut Foo { a: 1, b: Wrapping(2), c: None },
+            expected_bytes.as_bytes(),
+            &Foo { a: post_mutation_expected_a, b: Wrapping(2), c: None },
+        );
+        test::<_, 3>(
+            Unsized::from_mut_slice(&mut [1, 2, 3]),
+            &[1, 2, 3],
+            Unsized::from_mut_slice(&mut [0xFE, 2, 3]),
+        );
+    }
+
+    #[test]
+    fn test_array() {
+        #[derive(FromBytes, IntoBytes, Immutable)]
+        #[repr(C)]
+        struct Foo {
+            a: [u16; 33],
+        }
+
+        let foo = Foo { a: [0xFFFF; 33] };
+        let expected = [0xFFu8; 66];
+        assert_eq!(foo.as_bytes(), &expected[..]);
+    }
+
+    #[test]
+    fn test_new_zeroed() {
+        assert!(!bool::new_zeroed());
+        assert_eq!(u64::new_zeroed(), 0);
+        // This test exists in order to exercise unsafe code, especially when
+        // running under Miri.
+        #[allow(clippy::unit_cmp)]
+        {
+            assert_eq!(<()>::new_zeroed(), ());
+        }
+    }
+
+    #[test]
+    fn test_transparent_packed_generic_struct() {
+        #[derive(IntoBytes, FromBytes, Unaligned)]
+        #[repr(transparent)]
+        #[allow(dead_code)] // We never construct this type
+        struct Foo<T> {
+            _t: T,
+            _phantom: PhantomData<()>,
+        }
+
+        assert_impl_all!(Foo<u32>: FromZeros, FromBytes, IntoBytes);
+        assert_impl_all!(Foo<u8>: Unaligned);
+
+        #[derive(IntoBytes, FromBytes, Unaligned)]
+        #[repr(C, packed)]
+        #[allow(dead_code)] // We never construct this type
+        struct Bar<T, U> {
+            _t: T,
+            _u: U,
+        }
+
+        assert_impl_all!(Bar<u8, AU64>: FromZeros, FromBytes, IntoBytes, Unaligned);
+    }
+
+    #[cfg(feature = "alloc")]
+    mod alloc {
+        use super::*;
+
+        #[cfg(not(no_zerocopy_panic_in_const_and_vec_try_reserve_1_57_0))]
+        #[test]
+        fn test_extend_vec_zeroed() {
+            // Test extending when there is an existing allocation.
+            let mut v = vec![100u16, 200, 300];
+            FromZeros::extend_vec_zeroed(&mut v, 3).unwrap();
+            assert_eq!(v.len(), 6);
+            assert_eq!(&*v, &[100, 200, 300, 0, 0, 0]);
+            drop(v);
+
+            // Test extending when there is no existing allocation.
+            let mut v: Vec<u64> = Vec::new();
+            FromZeros::extend_vec_zeroed(&mut v, 3).unwrap();
+            assert_eq!(v.len(), 3);
+            assert_eq!(&*v, &[0, 0, 0]);
+            drop(v);
+        }
+
+        #[cfg(not(no_zerocopy_panic_in_const_and_vec_try_reserve_1_57_0))]
+        #[test]
+        fn test_extend_vec_zeroed_zst() {
+            // Test extending when there is an existing (fake) allocation.
+            let mut v = vec![(), (), ()];
+            <()>::extend_vec_zeroed(&mut v, 3).unwrap();
+            assert_eq!(v.len(), 6);
+            assert_eq!(&*v, &[(), (), (), (), (), ()]);
+            drop(v);
+
+            // Test extending when there is no existing (fake) allocation.
+            let mut v: Vec<()> = Vec::new();
+            <()>::extend_vec_zeroed(&mut v, 3).unwrap();
+            assert_eq!(&*v, &[(), (), ()]);
+            drop(v);
+        }
+
+        #[cfg(not(no_zerocopy_panic_in_const_and_vec_try_reserve_1_57_0))]
+        #[test]
+        fn test_insert_vec_zeroed() {
+            // Insert at start (no existing allocation).
+            let mut v: Vec<u64> = Vec::new();
+            u64::insert_vec_zeroed(&mut v, 0, 2).unwrap();
+            assert_eq!(v.len(), 2);
+            assert_eq!(&*v, &[0, 0]);
+            drop(v);
+
+            // Insert at start.
+            let mut v = vec![100u64, 200, 300];
+            u64::insert_vec_zeroed(&mut v, 0, 2).unwrap();
+            assert_eq!(v.len(), 5);
+            assert_eq!(&*v, &[0, 0, 100, 200, 300]);
+            drop(v);
+
+            // Insert at middle.
+            let mut v = vec![100u64, 200, 300];
+            u64::insert_vec_zeroed(&mut v, 1, 1).unwrap();
+            assert_eq!(v.len(), 4);
+            assert_eq!(&*v, &[100, 0, 200, 300]);
+            drop(v);
+
+            // Insert at end.
+            let mut v = vec![100u64, 200, 300];
+            u64::insert_vec_zeroed(&mut v, 3, 1).unwrap();
+            assert_eq!(v.len(), 4);
+            assert_eq!(&*v, &[100, 200, 300, 0]);
+            drop(v);
+        }
+
+        #[cfg(not(no_zerocopy_panic_in_const_and_vec_try_reserve_1_57_0))]
+        #[test]
+        fn test_insert_vec_zeroed_zst() {
+            // Insert at start (no existing fake allocation).
+            let mut v: Vec<()> = Vec::new();
+            <()>::insert_vec_zeroed(&mut v, 0, 2).unwrap();
+            assert_eq!(v.len(), 2);
+            assert_eq!(&*v, &[(), ()]);
+            drop(v);
+
+            // Insert at start.
+            let mut v = vec![(), (), ()];
+            <()>::insert_vec_zeroed(&mut v, 0, 2).unwrap();
+            assert_eq!(v.len(), 5);
+            assert_eq!(&*v, &[(), (), (), (), ()]);
+            drop(v);
+
+            // Insert at middle.
+            let mut v = vec![(), (), ()];
+            <()>::insert_vec_zeroed(&mut v, 1, 1).unwrap();
+            assert_eq!(v.len(), 4);
+            assert_eq!(&*v, &[(), (), (), ()]);
+            drop(v);
+
+            // Insert at end.
+            let mut v = vec![(), (), ()];
+            <()>::insert_vec_zeroed(&mut v, 3, 1).unwrap();
+            assert_eq!(v.len(), 4);
+            assert_eq!(&*v, &[(), (), (), ()]);
+            drop(v);
+        }
+
+        #[test]
+        fn test_new_box_zeroed() {
+            assert_eq!(u64::new_box_zeroed(), Ok(Box::new(0)));
+        }
+
+        #[test]
+        fn test_new_box_zeroed_array() {
+            drop(<[u32; 0x1000]>::new_box_zeroed());
+        }
+
+        #[test]
+        fn test_new_box_zeroed_zst() {
+            // This test exists in order to exercise unsafe code, especially
+            // when running under Miri.
+            #[allow(clippy::unit_cmp)]
+            {
+                assert_eq!(<()>::new_box_zeroed(), Ok(Box::new(())));
+            }
+        }
+
+        #[test]
+        fn test_new_box_zeroed_with_elems() {
+            let mut s: Box<[u64]> = <[u64]>::new_box_zeroed_with_elems(3).unwrap();
+            assert_eq!(s.len(), 3);
+            assert_eq!(&*s, &[0, 0, 0]);
+            s[1] = 3;
+            assert_eq!(&*s, &[0, 3, 0]);
+        }
+
+        #[test]
+        fn test_new_box_zeroed_with_elems_empty() {
+            let s: Box<[u64]> = <[u64]>::new_box_zeroed_with_elems(0).unwrap();
+            assert_eq!(s.len(), 0);
+        }
+
+        #[test]
+        fn test_new_box_zeroed_with_elems_zst() {
+            let mut s: Box<[()]> = <[()]>::new_box_zeroed_with_elems(3).unwrap();
+            assert_eq!(s.len(), 3);
+            assert!(s.get(10).is_none());
+            // This test exists in order to exercise unsafe code, especially
+            // when running under Miri.
+            #[allow(clippy::unit_cmp)]
+            {
+                assert_eq!(s[1], ());
+            }
+            s[2] = ();
+        }
+
+        #[test]
+        fn test_new_box_zeroed_with_elems_zst_empty() {
+            let s: Box<[()]> = <[()]>::new_box_zeroed_with_elems(0).unwrap();
+            assert_eq!(s.len(), 0);
+        }
+
+        #[test]
+        fn new_box_zeroed_with_elems_errors() {
+            assert_eq!(<[u16]>::new_box_zeroed_with_elems(usize::MAX), Err(AllocError));
+
+            let max = <usize as core::convert::TryFrom<_>>::try_from(isize::MAX).unwrap();
+            assert_eq!(
+                <[u16]>::new_box_zeroed_with_elems((max / mem::size_of::<u16>()) + 1),
+                Err(AllocError)
+            );
+        }
+    }
+
+    #[test]
+    #[allow(deprecated)]
+    fn test_deprecated_from_bytes() {
+        let val = 0u32;
+        let bytes = val.as_bytes();
+
+        assert!(u32::ref_from(bytes).is_some());
+        // mut_from needs mut bytes
+        let mut val = 0u32;
+        let mut_bytes = val.as_mut_bytes();
+        assert!(u32::mut_from(mut_bytes).is_some());
+
+        assert!(u32::read_from(bytes).is_some());
+
+        let (slc, rest) = <u32>::slice_from_prefix(bytes, 0).unwrap();
+        assert!(slc.is_empty());
+        assert_eq!(rest.len(), 4);
+
+        let (rest, slc) = <u32>::slice_from_suffix(bytes, 0).unwrap();
+        assert!(slc.is_empty());
+        assert_eq!(rest.len(), 4);
+
+        let (slc, rest) = <u32>::mut_slice_from_prefix(mut_bytes, 0).unwrap();
+        assert!(slc.is_empty());
+        assert_eq!(rest.len(), 4);
+
+        let (rest, slc) = <u32>::mut_slice_from_suffix(mut_bytes, 0).unwrap();
+        assert!(slc.is_empty());
+        assert_eq!(rest.len(), 4);
+    }
+
+    #[test]
+    fn test_try_ref_from_prefix_suffix() {
+        use crate::util::testutil::Align;
+        let bytes = &Align::<[u8; 4], u32>::new([0u8; 4]).t[..];
+        let (r, rest): (&u32, &[u8]) = u32::try_ref_from_prefix(bytes).unwrap();
+        assert_eq!(*r, 0);
+        assert_eq!(rest.len(), 0);
+
+        let (rest, r): (&[u8], &u32) = u32::try_ref_from_suffix(bytes).unwrap();
+        assert_eq!(*r, 0);
+        assert_eq!(rest.len(), 0);
+    }
+
+    #[test]
+    fn test_raw_dangling() {
+        use crate::util::AsAddress;
+        let ptr: NonNull<u32> = u32::raw_dangling();
+        assert_eq!(AsAddress::addr(ptr), 1);
+
+        let ptr: NonNull<[u32]> = <[u32]>::raw_dangling();
+        assert_eq!(AsAddress::addr(ptr), 1);
+    }
+
+    #[test]
+    fn test_try_ref_from_prefix_with_elems() {
+        use crate::util::testutil::Align;
+        let bytes = &Align::<[u8; 8], u32>::new([0u8; 8]).t[..];
+        let (r, rest): (&[u32], &[u8]) = <[u32]>::try_ref_from_prefix_with_elems(bytes, 2).unwrap();
+        assert_eq!(r.len(), 2);
+        assert_eq!(rest.len(), 0);
+    }
+
+    #[test]
+    fn test_try_ref_from_suffix_with_elems() {
+        use crate::util::testutil::Align;
+        let bytes = &Align::<[u8; 8], u32>::new([0u8; 8]).t[..];
+        let (rest, r): (&[u8], &[u32]) = <[u32]>::try_ref_from_suffix_with_elems(bytes, 2).unwrap();
+        assert_eq!(r.len(), 2);
+        assert_eq!(rest.len(), 0);
+    }
+}