Merge tag 'trace-v7.3-2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-tracegrafted

Pull tracing fixes from Steven Rostedt:

 - Fix error output of boot instance creation failure

   Currently if a boot instance creation fails, instead of printing out
   the name of the instance that failed, it prints "(null)". That is
   because it prints "cur_str" that had already been processed by
   strsep(). Print the saved name instead.

   While at it, print the error code of the failure.

 - Fix use-after-free for same named historgrams

   Histograms can be named so that they can be used in multiple events.
   But if the named histogram has a variable attached, the second event
   that uses the named histogram which duplicates it and needs to free
   the original after duplication leaves the old variable in place and
   still visible. If another histogram uses than variable, it will use
   the stale one which will try to reference the freed duplicate
   histogram and crash the kernel.

   Free the duplicate variables along with the duplicated histogram
   data.

 - Check return value of kthread_run() in event self test

   The events self tests uses a kthread for testing but does not check
   if it succeeded in creating a kthread. If the kthread creation were
   to fail, the code will still try to call kthread_stop() on the error
   returned.

 - Fix race between reading trace_pipe and updating subbuffer size

   If a user is reading the trace_pipe file at the same time they update
   the ring buffer sub-buffer size, can cause the trace_pipe read to
   read stale data. Add trace_access_lock() around updating the ring
   buffer sub-buffer size.

 - Fix eventfs_inode on failure path in creation of the events directory

   In the creation of the "events" directory, if after allocating the
   eventfs_inode a failure is detected, it calls cleanup_ei() which
   calls free_ei(). The free_ei() will test if eventfs_inode being freed
   has no children. It is a bug if it does. But on the failure case of
   the creation of the "events" directory, the children lists have not
   yet been initialized and the free will trigger a warning because
   list_empty() on an uninitialized list returns false.

   Move the initialization into init_ei() where it makes more sense and
   makes sure that a created eventfs_inode has its lists initialized
   upon creation.

 - Check return value of kthread_run() in ftrace direct sample code

   The sample code that shows how to use the ftrace direct calls does
   not test the return of kthread_run() to see if it succeeds. Return a
   failure if the kthread_run() doesn't succeed.

 - Clear user events state on fork in case of alloc failure

   On fork, the child gets a pointer to the parent's user events state.
   It makes a copy of it then updates the child's pointer to it. But if
   the allocation fails, the duplication function leaves the child with
   a pointer to its parent's descriptor. When the child cleans up its
   data, it will free the parent's descriptor while the parent is still
   using it.

   In the duplication function, set the child's user_event_mm to NULL
   before testing if the allocation succeeded, and when it exits it will
   not free the parent's descriptor.

 - Fix retry exhaustion in simple ring buffer reader swap

   simple_ring_buffer_swap_reader_page() starts with retry set to 8 and
   post-decrements it only after a failed link replacement. On the final
   attempt, a successful replacement leaves retry at zero, while a
   failed replacement leaves it at -1.

   But the check for success expects the retry value to be non-zero and
   exits with an error on zero. This is the opposite result. Fix it.

 - Fail nicely when the remote swap_reader_page() returns an error

   Currently, if the swap_reader_page() of a remote buffer fails, it
   triggers a WARN_ON_ONCE() and continues normally. Instead, have it
   exit with an error and a pr_warn() print instead of a full WARNING.

* tag 'trace-v7.3-2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace:
  ring-buffer: Stop remote reader update when page swap fails
  tracing: Fix retry exhaustion in simple ring buffer reader swap
  tracing/user_events: Clear copied tracing state before fork duplication
  samples/ftrace: Fix kthread_stop() on ERR_PTR in ftrace-direct-multi-modify
  samples/ftrace: Fix kthread_stop() on ERR_PTR in ftrace-direct-modify
  eventfs: Initialize ei->children and ei->list in init_ei()
  tracing: Fix use-after-free in trace_pipe read on sub-buffer order change
  tracing: Fix crash passing ERR_PTR to kthread_stop()
  tracing: Fix use-after-free with same-name named triggers
  tracing: Fix logged instance name on creation failure

1 files changed, 1098 insertions, 0 deletions

diff --git a/rust/syn/token.rs b/rust/syn/token.rs
new file mode 100644
index 000000000..18345cc58
--- /dev/null
+++ b/rust/syn/token.rs
@@ -0,0 +1,1098 @@
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
+//! Tokens representing Rust punctuation, keywords, and delimiters.
+//!
+//! The type names in this module can be difficult to keep straight, so we
+//! prefer to use the [`Token!`] macro instead. This is a type-macro that
+//! expands to the token type of the given token.
+//!
+//! [`Token!`]: crate::Token
+//!
+//! # Example
+//!
+//! The [`ItemStatic`] syntax tree node is defined like this.
+//!
+//! [`ItemStatic`]: crate::ItemStatic
+//!
+//! ```
+//! # use syn::{Attribute, Expr, Ident, Token, Type, Visibility};
+//! #
+//! pub struct ItemStatic {
+//!     pub attrs: Vec<Attribute>,
+//!     pub vis: Visibility,
+//!     pub static_token: Token![static],
+//!     pub mutability: Option<Token![mut]>,
+//!     pub ident: Ident,
+//!     pub colon_token: Token![:],
+//!     pub ty: Box<Type>,
+//!     pub eq_token: Token![=],
+//!     pub expr: Box<Expr>,
+//!     pub semi_token: Token![;],
+//! }
+//! ```
+//!
+//! # Parsing
+//!
+//! Keywords and punctuation can be parsed through the [`ParseStream::parse`]
+//! method. Delimiter tokens are parsed using the [`parenthesized!`],
+//! [`bracketed!`] and [`braced!`] macros.
+//!
+//! [`ParseStream::parse`]: crate::parse::ParseBuffer::parse()
+//! [`parenthesized!`]: crate::parenthesized!
+//! [`bracketed!`]: crate::bracketed!
+//! [`braced!`]: crate::braced!
+//!
+//! ```
+//! use syn::{Attribute, Result};
+//! use syn::parse::{Parse, ParseStream};
+//! #
+//! # enum ItemStatic {}
+//!
+//! // Parse the ItemStatic struct shown above.
+//! impl Parse for ItemStatic {
+//!     fn parse(input: ParseStream) -> Result<Self> {
+//!         # use syn::ItemStatic;
+//!         # fn parse(input: ParseStream) -> Result<ItemStatic> {
+//!         Ok(ItemStatic {
+//!             attrs: input.call(Attribute::parse_outer)?,
+//!             vis: input.parse()?,
+//!             static_token: input.parse()?,
+//!             mutability: input.parse()?,
+//!             ident: input.parse()?,
+//!             colon_token: input.parse()?,
+//!             ty: input.parse()?,
+//!             eq_token: input.parse()?,
+//!             expr: input.parse()?,
+//!             semi_token: input.parse()?,
+//!         })
+//!         # }
+//!         # unimplemented!()
+//!     }
+//! }
+//! ```
+//!
+//! # Other operations
+//!
+//! Every keyword and punctuation token supports the following operations.
+//!
+//! - [Peeking] — `input.peek(Token![...])`
+//!
+//! - [Parsing] — `input.parse::<Token![...]>()?`
+//!
+//! - [Printing] — `quote!( ... #the_token ... )`
+//!
+//! - Construction from a [`Span`] — `let the_token = Token![...](sp)`
+//!
+//! - Field access to its span — `let sp = the_token.span`
+//!
+//! [Peeking]: crate::parse::ParseBuffer::peek()
+//! [Parsing]: crate::parse::ParseBuffer::parse()
+//! [Printing]: https://docs.rs/quote/1.0/quote/trait.ToTokens.html
+//! [`Span`]: https://docs.rs/proc-macro2/1.0/proc_macro2/struct.Span.html
+
+#[cfg(feature = "parsing")]
+pub(crate) use self::private::CustomToken;
+use self::private::WithSpan;
+#[cfg(feature = "parsing")]
+use crate::buffer::Cursor;
+#[cfg(feature = "parsing")]
+use crate::error::Result;
+#[cfg(feature = "parsing")]
+use crate::lifetime::Lifetime;
+#[cfg(feature = "parsing")]
+use crate::parse::{Parse, ParseStream};
+use crate::span::IntoSpans;
+use proc_macro2::extra::DelimSpan;
+use proc_macro2::Span;
+#[cfg(feature = "printing")]
+use proc_macro2::TokenStream;
+#[cfg(any(feature = "parsing", feature = "printing"))]
+use proc_macro2::{Delimiter, Ident};
+#[cfg(feature = "parsing")]
+use proc_macro2::{Literal, Punct, TokenTree};
+#[cfg(feature = "printing")]
+use quote::{ToTokens, TokenStreamExt};
+#[cfg(feature = "extra-traits")]
+use std::cmp;
+#[cfg(feature = "extra-traits")]
+use std::fmt::{self, Debug};
+#[cfg(feature = "extra-traits")]
+use std::hash::{Hash, Hasher};
+use std::ops::{Deref, DerefMut};
+
+/// Marker trait for types that represent single tokens.
+///
+/// This trait is sealed and cannot be implemented for types outside of Syn.
+#[cfg(feature = "parsing")]
+pub trait Token: private::Sealed {
+    // Not public API.
+    #[doc(hidden)]
+    fn peek(cursor: Cursor) -> bool;
+
+    // Not public API.
+    #[doc(hidden)]
+    fn display() -> &'static str;
+}
+
+pub(crate) mod private {
+    #[cfg(feature = "parsing")]
+    use crate::buffer::Cursor;
+    use proc_macro2::Span;
+
+    #[cfg(feature = "parsing")]
+    pub trait Sealed {}
+
+    /// Support writing `token.span` rather than `token.spans[0]` on tokens that
+    /// hold a single span.
+    #[repr(transparent)]
+    #[allow(unknown_lints, repr_transparent_external_private_fields)] // False positive: https://github.com/rust-lang/rust/issues/78586#issuecomment-1722680482
+    pub struct WithSpan {
+        pub span: Span,
+    }
+
+    // Not public API.
+    #[doc(hidden)]
+    #[cfg(feature = "parsing")]
+    pub trait CustomToken {
+        fn peek(cursor: Cursor) -> bool;
+        fn display() -> &'static str;
+    }
+}
+
+#[cfg(feature = "parsing")]
+impl private::Sealed for Ident {}
+
+macro_rules! impl_low_level_token {
+    ($display:literal $($path:ident)::+ $get:ident) => {
+        #[cfg(feature = "parsing")]
+        impl Token for $($path)::+ {
+            fn peek(cursor: Cursor) -> bool {
+                cursor.$get().is_some()
+            }
+
+            fn display() -> &'static str {
+                $display
+            }
+        }
+
+        #[cfg(feature = "parsing")]
+        impl private::Sealed for $($path)::+ {}
+    };
+}
+
+impl_low_level_token!("punctuation token" Punct punct);
+impl_low_level_token!("literal" Literal literal);
+impl_low_level_token!("token" TokenTree token_tree);
+impl_low_level_token!("group token" proc_macro2::Group any_group);
+impl_low_level_token!("lifetime" Lifetime lifetime);
+
+#[cfg(feature = "parsing")]
+impl<T: CustomToken> private::Sealed for T {}
+
+#[cfg(feature = "parsing")]
+impl<T: CustomToken> Token for T {
+    fn peek(cursor: Cursor) -> bool {
+        <Self as CustomToken>::peek(cursor)
+    }
+
+    fn display() -> &'static str {
+        <Self as CustomToken>::display()
+    }
+}
+
+macro_rules! define_keywords {
+    ($($token:literal pub struct $name:ident)*) => {
+        $(
+            #[doc = concat!('`', $token, '`')]
+            ///
+            /// Don't try to remember the name of this type &mdash; use the
+            /// [`Token!`] macro instead.
+            ///
+            /// [`Token!`]: crate::token
+            pub struct $name {
+                pub span: Span,
+            }
+
+            #[doc(hidden)]
+            #[allow(non_snake_case)]
+            pub fn $name<S: IntoSpans<Span>>(span: S) -> $name {
+                $name {
+                    span: span.into_spans(),
+                }
+            }
+
+            impl std::default::Default for $name {
+                fn default() -> Self {
+                    $name {
+                        span: Span::call_site(),
+                    }
+                }
+            }
+
+            #[cfg(feature = "clone-impls")]
+            #[cfg_attr(docsrs, doc(cfg(feature = "clone-impls")))]
+            impl Copy for $name {}
+
+            #[cfg(feature = "clone-impls")]
+            #[cfg_attr(docsrs, doc(cfg(feature = "clone-impls")))]
+            impl Clone for $name {
+                fn clone(&self) -> Self {
+                    *self
+                }
+            }
+
+            #[cfg(feature = "extra-traits")]
+            #[cfg_attr(docsrs, doc(cfg(feature = "extra-traits")))]
+            impl Debug for $name {
+                fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+                    f.write_str(stringify!($name))
+                }
+            }
+
+            #[cfg(feature = "extra-traits")]
+            #[cfg_attr(docsrs, doc(cfg(feature = "extra-traits")))]
+            impl cmp::Eq for $name {}
+
+            #[cfg(feature = "extra-traits")]
+            #[cfg_attr(docsrs, doc(cfg(feature = "extra-traits")))]
+            impl PartialEq for $name {
+                fn eq(&self, _other: &$name) -> bool {
+                    true
+                }
+            }
+
+            #[cfg(feature = "extra-traits")]
+            #[cfg_attr(docsrs, doc(cfg(feature = "extra-traits")))]
+            impl Hash for $name {
+                fn hash<H: Hasher>(&self, _state: &mut H) {}
+            }
+
+            #[cfg(feature = "printing")]
+            #[cfg_attr(docsrs, doc(cfg(feature = "printing")))]
+            impl ToTokens for $name {
+                fn to_tokens(&self, tokens: &mut TokenStream) {
+                    printing::keyword($token, self.span, tokens);
+                }
+            }
+
+            #[cfg(feature = "parsing")]
+            #[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
+            impl Parse for $name {
+                fn parse(input: ParseStream) -> Result<Self> {
+                    Ok($name {
+                        span: parsing::keyword(input, $token)?,
+                    })
+                }
+            }
+
+            #[cfg(feature = "parsing")]
+            impl Token for $name {
+                fn peek(cursor: Cursor) -> bool {
+                    parsing::peek_keyword(cursor, $token)
+                }
+
+                fn display() -> &'static str {
+                    concat!("`", $token, "`")
+                }
+            }
+
+            #[cfg(feature = "parsing")]
+            impl private::Sealed for $name {}
+        )*
+    };
+}
+
+macro_rules! impl_deref_if_len_is_1 {
+    ($name:ident/1) => {
+        impl Deref for $name {
+            type Target = WithSpan;
+
+            fn deref(&self) -> &Self::Target {
+                unsafe { &*(self as *const Self).cast::<WithSpan>() }
+            }
+        }
+
+        impl DerefMut for $name {
+            fn deref_mut(&mut self) -> &mut Self::Target {
+                unsafe { &mut *(self as *mut Self).cast::<WithSpan>() }
+            }
+        }
+    };
+
+    ($name:ident/$len:literal) => {};
+}
+
+macro_rules! define_punctuation_structs {
+    ($($token:literal pub struct $name:ident/$len:tt #[doc = $usage:literal])*) => {
+        $(
+            #[cfg_attr(not(doc), repr(transparent))]
+            #[allow(unknown_lints, repr_transparent_external_private_fields)] // False positive: https://github.com/rust-lang/rust/issues/78586#issuecomment-1722680482
+            #[doc = concat!('`', $token, '`')]
+            ///
+            /// Usage:
+            #[doc = concat!($usage, '.')]
+            ///
+            /// Don't try to remember the name of this type &mdash; use the
+            /// [`Token!`] macro instead.
+            ///
+            /// [`Token!`]: crate::token
+            pub struct $name {
+                pub spans: [Span; $len],
+            }
+
+            #[doc(hidden)]
+            #[allow(non_snake_case)]
+            pub fn $name<S: IntoSpans<[Span; $len]>>(spans: S) -> $name {
+                $name {
+                    spans: spans.into_spans(),
+                }
+            }
+
+            impl std::default::Default for $name {
+                fn default() -> Self {
+                    $name {
+                        spans: [Span::call_site(); $len],
+                    }
+                }
+            }
+
+            #[cfg(feature = "clone-impls")]
+            #[cfg_attr(docsrs, doc(cfg(feature = "clone-impls")))]
+            impl Copy for $name {}
+
+            #[cfg(feature = "clone-impls")]
+            #[cfg_attr(docsrs, doc(cfg(feature = "clone-impls")))]
+            impl Clone for $name {
+                fn clone(&self) -> Self {
+                    *self
+                }
+            }
+
+            #[cfg(feature = "extra-traits")]
+            #[cfg_attr(docsrs, doc(cfg(feature = "extra-traits")))]
+            impl Debug for $name {
+                fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+                    f.write_str(stringify!($name))
+                }
+            }
+
+            #[cfg(feature = "extra-traits")]
+            #[cfg_attr(docsrs, doc(cfg(feature = "extra-traits")))]
+            impl cmp::Eq for $name {}
+
+            #[cfg(feature = "extra-traits")]
+            #[cfg_attr(docsrs, doc(cfg(feature = "extra-traits")))]
+            impl PartialEq for $name {
+                fn eq(&self, _other: &$name) -> bool {
+                    true
+                }
+            }
+
+            #[cfg(feature = "extra-traits")]
+            #[cfg_attr(docsrs, doc(cfg(feature = "extra-traits")))]
+            impl Hash for $name {
+                fn hash<H: Hasher>(&self, _state: &mut H) {}
+            }
+
+            impl_deref_if_len_is_1!($name/$len);
+        )*
+    };
+}
+
+macro_rules! define_punctuation {
+    ($($token:literal pub struct $name:ident/$len:tt #[doc = $usage:literal])*) => {
+        $(
+            define_punctuation_structs! {
+                $token pub struct $name/$len #[doc = $usage]
+            }
+
+            #[cfg(feature = "printing")]
+            #[cfg_attr(docsrs, doc(cfg(feature = "printing")))]
+            impl ToTokens for $name {
+                fn to_tokens(&self, tokens: &mut TokenStream) {
+                    printing::punct($token, &self.spans, tokens);
+                }
+            }
+
+            #[cfg(feature = "parsing")]
+            #[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
+            impl Parse for $name {
+                fn parse(input: ParseStream) -> Result<Self> {
+                    Ok($name {
+                        spans: parsing::punct(input, $token)?,
+                    })
+                }
+            }
+
+            #[cfg(feature = "parsing")]
+            impl Token for $name {
+                fn peek(cursor: Cursor) -> bool {
+                    parsing::peek_punct(cursor, $token)
+                }
+
+                fn display() -> &'static str {
+                    concat!("`", $token, "`")
+                }
+            }
+
+            #[cfg(feature = "parsing")]
+            impl private::Sealed for $name {}
+        )*
+    };
+}
+
+macro_rules! define_delimiters {
+    ($($delim:ident pub struct $name:ident #[$doc:meta])*) => {
+        $(
+            #[$doc]
+            pub struct $name {
+                pub span: DelimSpan,
+            }
+
+            #[doc(hidden)]
+            #[allow(non_snake_case)]
+            pub fn $name<S: IntoSpans<DelimSpan>>(span: S) -> $name {
+                $name {
+                    span: span.into_spans(),
+                }
+            }
+
+            impl std::default::Default for $name {
+                fn default() -> Self {
+                    $name(Span::call_site())
+                }
+            }
+
+            #[cfg(feature = "clone-impls")]
+            #[cfg_attr(docsrs, doc(cfg(feature = "clone-impls")))]
+            impl Copy for $name {}
+
+            #[cfg(feature = "clone-impls")]
+            #[cfg_attr(docsrs, doc(cfg(feature = "clone-impls")))]
+            impl Clone for $name {
+                fn clone(&self) -> Self {
+                    *self
+                }
+            }
+
+            #[cfg(feature = "extra-traits")]
+            #[cfg_attr(docsrs, doc(cfg(feature = "extra-traits")))]
+            impl Debug for $name {
+                fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+                    f.write_str(stringify!($name))
+                }
+            }
+
+            #[cfg(feature = "extra-traits")]
+            #[cfg_attr(docsrs, doc(cfg(feature = "extra-traits")))]
+            impl cmp::Eq for $name {}
+
+            #[cfg(feature = "extra-traits")]
+            #[cfg_attr(docsrs, doc(cfg(feature = "extra-traits")))]
+            impl PartialEq for $name {
+                fn eq(&self, _other: &$name) -> bool {
+                    true
+                }
+            }
+
+            #[cfg(feature = "extra-traits")]
+            #[cfg_attr(docsrs, doc(cfg(feature = "extra-traits")))]
+            impl Hash for $name {
+                fn hash<H: Hasher>(&self, _state: &mut H) {}
+            }
+
+            impl $name {
+                #[cfg(feature = "printing")]
+                #[cfg_attr(docsrs, doc(cfg(feature = "printing")))]
+                pub fn surround<F>(&self, tokens: &mut TokenStream, f: F)
+                where
+                    F: FnOnce(&mut TokenStream),
+                {
+                    let mut inner = TokenStream::new();
+                    f(&mut inner);
+                    printing::delim(Delimiter::$delim, self.span.join(), tokens, inner);
+                }
+            }
+
+            #[cfg(feature = "parsing")]
+            impl private::Sealed for $name {}
+        )*
+    };
+}
+
+define_punctuation_structs! {
+    "_" pub struct Underscore/1 /// wildcard patterns, inferred types, unnamed items in constants, extern crates, use declarations, and destructuring assignment
+}
+
+#[cfg(feature = "printing")]
+#[cfg_attr(docsrs, doc(cfg(feature = "printing")))]
+impl ToTokens for Underscore {
+    fn to_tokens(&self, tokens: &mut TokenStream) {
+        tokens.append(Ident::new("_", self.span));
+    }
+}
+
+#[cfg(feature = "parsing")]
+#[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
+impl Parse for Underscore {
+    fn parse(input: ParseStream) -> Result<Self> {
+        input.step(|cursor| {
+            if let Some((ident, rest)) = cursor.ident() {
+                if ident == "_" {
+                    return Ok((Underscore(ident.span()), rest));
+                }
+            }
+            if let Some((punct, rest)) = cursor.punct() {
+                if punct.as_char() == '_' {
+                    return Ok((Underscore(punct.span()), rest));
+                }
+            }
+            Err(cursor.error("expected `_`"))
+        })
+    }
+}
+
+#[cfg(feature = "parsing")]
+impl Token for Underscore {
+    fn peek(cursor: Cursor) -> bool {
+        if let Some((ident, _rest)) = cursor.ident() {
+            return ident == "_";
+        }
+        if let Some((punct, _rest)) = cursor.punct() {
+            return punct.as_char() == '_';
+        }
+        false
+    }
+
+    fn display() -> &'static str {
+        "`_`"
+    }
+}
+
+#[cfg(feature = "parsing")]
+impl private::Sealed for Underscore {}
+
+/// None-delimited group
+pub struct Group {
+    pub span: Span,
+}
+
+#[doc(hidden)]
+#[allow(non_snake_case)]
+pub fn Group<S: IntoSpans<Span>>(span: S) -> Group {
+    Group {
+        span: span.into_spans(),
+    }
+}
+
+impl std::default::Default for Group {
+    fn default() -> Self {
+        Group {
+            span: Span::call_site(),
+        }
+    }
+}
+
+#[cfg(feature = "clone-impls")]
+#[cfg_attr(docsrs, doc(cfg(feature = "clone-impls")))]
+impl Copy for Group {}
+
+#[cfg(feature = "clone-impls")]
+#[cfg_attr(docsrs, doc(cfg(feature = "clone-impls")))]
+impl Clone for Group {
+    fn clone(&self) -> Self {
+        *self
+    }
+}
+
+#[cfg(feature = "extra-traits")]
+#[cfg_attr(docsrs, doc(cfg(feature = "extra-traits")))]
+impl Debug for Group {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.write_str("Group")
+    }
+}
+
+#[cfg(feature = "extra-traits")]
+#[cfg_attr(docsrs, doc(cfg(feature = "extra-traits")))]
+impl cmp::Eq for Group {}
+
+#[cfg(feature = "extra-traits")]
+#[cfg_attr(docsrs, doc(cfg(feature = "extra-traits")))]
+impl PartialEq for Group {
+    fn eq(&self, _other: &Group) -> bool {
+        true
+    }
+}
+
+#[cfg(feature = "extra-traits")]
+#[cfg_attr(docsrs, doc(cfg(feature = "extra-traits")))]
+impl Hash for Group {
+    fn hash<H: Hasher>(&self, _state: &mut H) {}
+}
+
+impl Group {
+    #[cfg(feature = "printing")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "printing")))]
+    pub fn surround<F>(&self, tokens: &mut TokenStream, f: F)
+    where
+        F: FnOnce(&mut TokenStream),
+    {
+        let mut inner = TokenStream::new();
+        f(&mut inner);
+        printing::delim(Delimiter::None, self.span, tokens, inner);
+    }
+}
+
+#[cfg(feature = "parsing")]
+impl private::Sealed for Group {}
+
+#[cfg(feature = "parsing")]
+impl Token for Paren {
+    fn peek(cursor: Cursor) -> bool {
+        cursor.group(Delimiter::Parenthesis).is_some()
+    }
+
+    fn display() -> &'static str {
+        "parentheses"
+    }
+}
+
+#[cfg(feature = "parsing")]
+impl Token for Brace {
+    fn peek(cursor: Cursor) -> bool {
+        cursor.group(Delimiter::Brace).is_some()
+    }
+
+    fn display() -> &'static str {
+        "curly braces"
+    }
+}
+
+#[cfg(feature = "parsing")]
+impl Token for Bracket {
+    fn peek(cursor: Cursor) -> bool {
+        cursor.group(Delimiter::Bracket).is_some()
+    }
+
+    fn display() -> &'static str {
+        "square brackets"
+    }
+}
+
+#[cfg(feature = "parsing")]
+impl Token for Group {
+    fn peek(cursor: Cursor) -> bool {
+        cursor.group(Delimiter::None).is_some()
+    }
+
+    fn display() -> &'static str {
+        "invisible group"
+    }
+}
+
+define_keywords! {
+    "abstract"    pub struct Abstract
+    "as"          pub struct As
+    "async"       pub struct Async
+    "auto"        pub struct Auto
+    "await"       pub struct Await
+    "become"      pub struct Become
+    "box"         pub struct Box
+    "break"       pub struct Break
+    "const"       pub struct Const
+    "continue"    pub struct Continue
+    "crate"       pub struct Crate
+    "default"     pub struct Default
+    "do"          pub struct Do
+    "dyn"         pub struct Dyn
+    "else"        pub struct Else
+    "enum"        pub struct Enum
+    "extern"      pub struct Extern
+    "final"       pub struct Final
+    "fn"          pub struct Fn
+    "for"         pub struct For
+    "if"          pub struct If
+    "impl"        pub struct Impl
+    "in"          pub struct In
+    "let"         pub struct Let
+    "loop"        pub struct Loop
+    "macro"       pub struct Macro
+    "match"       pub struct Match
+    "mod"         pub struct Mod
+    "move"        pub struct Move
+    "mut"         pub struct Mut
+    "override"    pub struct Override
+    "priv"        pub struct Priv
+    "pub"         pub struct Pub
+    "raw"         pub struct Raw
+    "ref"         pub struct Ref
+    "return"      pub struct Return
+    "Self"        pub struct SelfType
+    "self"        pub struct SelfValue
+    "static"      pub struct Static
+    "struct"      pub struct Struct
+    "super"       pub struct Super
+    "trait"       pub struct Trait
+    "try"         pub struct Try
+    "type"        pub struct Type
+    "typeof"      pub struct Typeof
+    "union"       pub struct Union
+    "unsafe"      pub struct Unsafe
+    "unsized"     pub struct Unsized
+    "use"         pub struct Use
+    "virtual"     pub struct Virtual
+    "where"       pub struct Where
+    "while"       pub struct While
+    "yield"       pub struct Yield
+}
+
+define_punctuation! {
+    "&"           pub struct And/1        /// bitwise and logical AND, borrow, references, reference patterns
+    "&&"          pub struct AndAnd/2     /// lazy AND, borrow, references, reference patterns
+    "&="          pub struct AndEq/2      /// bitwise AND assignment
+    "@"           pub struct At/1         /// subpattern binding
+    "^"           pub struct Caret/1      /// bitwise and logical XOR
+    "^="          pub struct CaretEq/2    /// bitwise XOR assignment
+    ":"           pub struct Colon/1      /// various separators
+    ","           pub struct Comma/1      /// various separators
+    "$"           pub struct Dollar/1     /// macros
+    "."           pub struct Dot/1        /// field access, tuple index
+    ".."          pub struct DotDot/2     /// range, struct expressions, patterns, range patterns
+    "..."         pub struct DotDotDot/3  /// variadic functions, range patterns
+    "..="         pub struct DotDotEq/3   /// inclusive range, range patterns
+    "="           pub struct Eq/1         /// assignment, attributes, various type definitions
+    "=="          pub struct EqEq/2       /// equal
+    "=>"          pub struct FatArrow/2   /// match arms, macros
+    ">="          pub struct Ge/2         /// greater than or equal to, generics
+    ">"           pub struct Gt/1         /// greater than, generics, paths
+    "<-"          pub struct LArrow/2     /// unused
+    "<="          pub struct Le/2         /// less than or equal to
+    "<"           pub struct Lt/1         /// less than, generics, paths
+    "-"           pub struct Minus/1      /// subtraction, negation
+    "-="          pub struct MinusEq/2    /// subtraction assignment
+    "!="          pub struct Ne/2         /// not equal
+    "!"           pub struct Not/1        /// bitwise and logical NOT, macro calls, inner attributes, never type, negative impls
+    "|"           pub struct Or/1         /// bitwise and logical OR, closures, patterns in match, if let, and while let
+    "|="          pub struct OrEq/2       /// bitwise OR assignment
+    "||"          pub struct OrOr/2       /// lazy OR, closures
+    "::"          pub struct PathSep/2    /// path separator
+    "%"           pub struct Percent/1    /// remainder
+    "%="          pub struct PercentEq/2  /// remainder assignment
+    "+"           pub struct Plus/1       /// addition, trait bounds, macro Kleene matcher
+    "+="          pub struct PlusEq/2     /// addition assignment
+    "#"           pub struct Pound/1      /// attributes
+    "?"           pub struct Question/1   /// question mark operator, questionably sized, macro Kleene matcher
+    "->"          pub struct RArrow/2     /// function return type, closure return type, function pointer type
+    ";"           pub struct Semi/1       /// terminator for various items and statements, array types
+    "<<"          pub struct Shl/2        /// shift left, nested generics
+    "<<="         pub struct ShlEq/3      /// shift left assignment
+    ">>"          pub struct Shr/2        /// shift right, nested generics
+    ">>="         pub struct ShrEq/3      /// shift right assignment, nested generics
+    "/"           pub struct Slash/1      /// division
+    "/="          pub struct SlashEq/2    /// division assignment
+    "*"           pub struct Star/1       /// multiplication, dereference, raw pointers, macro Kleene matcher, use wildcards
+    "*="          pub struct StarEq/2     /// multiplication assignment
+    "~"           pub struct Tilde/1      /// unused since before Rust 1.0
+}
+
+define_delimiters! {
+    Brace         pub struct Brace        /// `{`&hellip;`}`
+    Bracket       pub struct Bracket      /// `[`&hellip;`]`
+    Parenthesis   pub struct Paren        /// `(`&hellip;`)`
+}
+
+/// A type-macro that expands to the name of the Rust type representation of a
+/// given token.
+///
+/// As a type, `Token!` is commonly used in the type of struct fields, the type
+/// of a `let` statement, or in turbofish for a `parse` function.
+///
+/// ```
+/// use syn::{Ident, Token};
+/// use syn::parse::{Parse, ParseStream, Result};
+///
+/// // `struct Foo;`
+/// pub struct UnitStruct {
+///     struct_token: Token![struct],
+///     ident: Ident,
+///     semi_token: Token![;],
+/// }
+///
+/// impl Parse for UnitStruct {
+///     fn parse(input: ParseStream) -> Result<Self> {
+///         let struct_token: Token![struct] = input.parse()?;
+///         let ident: Ident = input.parse()?;
+///         let semi_token = input.parse::<Token![;]>()?;
+///         Ok(UnitStruct { struct_token, ident, semi_token })
+///     }
+/// }
+/// ```
+///
+/// As an expression, `Token!` is used for peeking tokens or instantiating
+/// tokens from a span.
+///
+/// ```
+/// # use syn::{Ident, Token};
+/// # use syn::parse::{Parse, ParseStream, Result};
+/// #
+/// # struct UnitStruct {
+/// #     struct_token: Token![struct],
+/// #     ident: Ident,
+/// #     semi_token: Token![;],
+/// # }
+/// #
+/// # impl Parse for UnitStruct {
+/// #     fn parse(input: ParseStream) -> Result<Self> {
+/// #         unimplemented!()
+/// #     }
+/// # }
+/// #
+/// fn make_unit_struct(name: Ident) -> UnitStruct {
+///     let span = name.span();
+///     UnitStruct {
+///         struct_token: Token![struct](span),
+///         ident: name,
+///         semi_token: Token![;](span),
+///     }
+/// }
+///
+/// # fn parse(input: ParseStream) -> Result<()> {
+/// if input.peek(Token![struct]) {
+///     let unit_struct: UnitStruct = input.parse()?;
+///     /* ... */
+/// }
+/// # Ok(())
+/// # }
+/// ```
+///
+/// See the [token module] documentation for details and examples.
+///
+/// [token module]: crate::token
+#[macro_export]
+macro_rules! Token {
+    [abstract]    => { $crate::token::Abstract };
+    [as]          => { $crate::token::As };
+    [async]       => { $crate::token::Async };
+    [auto]        => { $crate::token::Auto };
+    [await]       => { $crate::token::Await };
+    [become]      => { $crate::token::Become };
+    [box]         => { $crate::token::Box };
+    [break]       => { $crate::token::Break };
+    [const]       => { $crate::token::Const };
+    [continue]    => { $crate::token::Continue };
+    [crate]       => { $crate::token::Crate };
+    [default]     => { $crate::token::Default };
+    [do]          => { $crate::token::Do };
+    [dyn]         => { $crate::token::Dyn };
+    [else]        => { $crate::token::Else };
+    [enum]        => { $crate::token::Enum };
+    [extern]      => { $crate::token::Extern };
+    [final]       => { $crate::token::Final };
+    [fn]          => { $crate::token::Fn };
+    [for]         => { $crate::token::For };
+    [if]          => { $crate::token::If };
+    [impl]        => { $crate::token::Impl };
+    [in]          => { $crate::token::In };
+    [let]         => { $crate::token::Let };
+    [loop]        => { $crate::token::Loop };
+    [macro]       => { $crate::token::Macro };
+    [match]       => { $crate::token::Match };
+    [mod]         => { $crate::token::Mod };
+    [move]        => { $crate::token::Move };
+    [mut]         => { $crate::token::Mut };
+    [override]    => { $crate::token::Override };
+    [priv]        => { $crate::token::Priv };
+    [pub]         => { $crate::token::Pub };
+    [raw]         => { $crate::token::Raw };
+    [ref]         => { $crate::token::Ref };
+    [return]      => { $crate::token::Return };
+    [Self]        => { $crate::token::SelfType };
+    [self]        => { $crate::token::SelfValue };
+    [static]      => { $crate::token::Static };
+    [struct]      => { $crate::token::Struct };
+    [super]       => { $crate::token::Super };
+    [trait]       => { $crate::token::Trait };
+    [try]         => { $crate::token::Try };
+    [type]        => { $crate::token::Type };
+    [typeof]      => { $crate::token::Typeof };
+    [union]       => { $crate::token::Union };
+    [unsafe]      => { $crate::token::Unsafe };
+    [unsized]     => { $crate::token::Unsized };
+    [use]         => { $crate::token::Use };
+    [virtual]     => { $crate::token::Virtual };
+    [where]       => { $crate::token::Where };
+    [while]       => { $crate::token::While };
+    [yield]       => { $crate::token::Yield };
+    [&]           => { $crate::token::And };
+    [&&]          => { $crate::token::AndAnd };
+    [&=]          => { $crate::token::AndEq };
+    [@]           => { $crate::token::At };
+    [^]           => { $crate::token::Caret };
+    [^=]          => { $crate::token::CaretEq };
+    [:]           => { $crate::token::Colon };
+    [,]           => { $crate::token::Comma };
+    [$]           => { $crate::token::Dollar };
+    [.]           => { $crate::token::Dot };
+    [..]          => { $crate::token::DotDot };
+    [...]         => { $crate::token::DotDotDot };
+    [..=]         => { $crate::token::DotDotEq };
+    [=]           => { $crate::token::Eq };
+    [==]          => { $crate::token::EqEq };
+    [=>]          => { $crate::token::FatArrow };
+    [>=]          => { $crate::token::Ge };
+    [>]           => { $crate::token::Gt };
+    [<-]          => { $crate::token::LArrow };
+    [<=]          => { $crate::token::Le };
+    [<]           => { $crate::token::Lt };
+    [-]           => { $crate::token::Minus };
+    [-=]          => { $crate::token::MinusEq };
+    [!=]          => { $crate::token::Ne };
+    [!]           => { $crate::token::Not };
+    [|]           => { $crate::token::Or };
+    [|=]          => { $crate::token::OrEq };
+    [||]          => { $crate::token::OrOr };
+    [::]          => { $crate::token::PathSep };
+    [%]           => { $crate::token::Percent };
+    [%=]          => { $crate::token::PercentEq };
+    [+]           => { $crate::token::Plus };
+    [+=]          => { $crate::token::PlusEq };
+    [#]           => { $crate::token::Pound };
+    [?]           => { $crate::token::Question };
+    [->]          => { $crate::token::RArrow };
+    [;]           => { $crate::token::Semi };
+    [<<]          => { $crate::token::Shl };
+    [<<=]         => { $crate::token::ShlEq };
+    [>>]          => { $crate::token::Shr };
+    [>>=]         => { $crate::token::ShrEq };
+    [/]           => { $crate::token::Slash };
+    [/=]          => { $crate::token::SlashEq };
+    [*]           => { $crate::token::Star };
+    [*=]          => { $crate::token::StarEq };
+    [~]           => { $crate::token::Tilde };
+    [_]           => { $crate::token::Underscore };
+}
+
+// Not public API.
+#[doc(hidden)]
+#[cfg(feature = "parsing")]
+pub(crate) mod parsing {
+    use crate::buffer::Cursor;
+    use crate::error::{Error, Result};
+    use crate::parse::ParseStream;
+    use proc_macro2::{Spacing, Span};
+
+    pub(crate) fn keyword(input: ParseStream, token: &str) -> Result<Span> {
+        input.step(|cursor| {
+            if let Some((ident, rest)) = cursor.ident() {
+                if ident == token {
+                    return Ok((ident.span(), rest));
+                }
+            }
+            Err(cursor.error(format!("expected `{}`", token)))
+        })
+    }
+
+    pub(crate) fn peek_keyword(cursor: Cursor, token: &str) -> bool {
+        if let Some((ident, _rest)) = cursor.ident() {
+            ident == token
+        } else {
+            false
+        }
+    }
+
+    #[doc(hidden)]
+    pub fn punct<const N: usize>(input: ParseStream, token: &str) -> Result<[Span; N]> {
+        let mut spans = [input.span(); N];
+        punct_helper(input, token, &mut spans)?;
+        Ok(spans)
+    }
+
+    fn punct_helper(input: ParseStream, token: &str, spans: &mut [Span]) -> Result<()> {
+        input.step(|cursor| {
+            let mut cursor = *cursor;
+            assert_eq!(token.len(), spans.len());
+
+            for (i, ch) in token.chars().enumerate() {
+                match cursor.punct() {
+                    Some((punct, rest)) => {
+                        spans[i] = punct.span();
+                        if punct.as_char() != ch {
+                            break;
+                        } else if i == token.len() - 1 {
+                            return Ok(((), rest));
+                        } else if punct.spacing() != Spacing::Joint {
+                            break;
+                        }
+                        cursor = rest;
+                    }
+                    None => break,
+                }
+            }
+
+            Err(Error::new(spans[0], format!("expected `{}`", token)))
+        })
+    }
+
+    #[doc(hidden)]
+    pub fn peek_punct(mut cursor: Cursor, token: &str) -> bool {
+        for (i, ch) in token.chars().enumerate() {
+            match cursor.punct() {
+                Some((punct, rest)) => {
+                    if punct.as_char() != ch {
+                        break;
+                    } else if i == token.len() - 1 {
+                        return true;
+                    } else if punct.spacing() != Spacing::Joint {
+                        break;
+                    }
+                    cursor = rest;
+                }
+                None => break,
+            }
+        }
+        false
+    }
+}
+
+// Not public API.
+#[doc(hidden)]
+#[cfg(feature = "printing")]
+pub(crate) mod printing {
+    use proc_macro2::{Delimiter, Group, Ident, Punct, Spacing, Span, TokenStream};
+    use quote::TokenStreamExt;
+
+    #[doc(hidden)]
+    pub fn punct(s: &str, spans: &[Span], tokens: &mut TokenStream) {
+        assert_eq!(s.len(), spans.len());
+
+        let mut chars = s.chars();
+        let mut spans = spans.iter();
+        let ch = chars.next_back().unwrap();
+        let span = spans.next_back().unwrap();
+        for (ch, span) in chars.zip(spans) {
+            let mut op = Punct::new(ch, Spacing::Joint);
+            op.set_span(*span);
+            tokens.append(op);
+        }
+
+        let mut op = Punct::new(ch, Spacing::Alone);
+        op.set_span(*span);
+        tokens.append(op);
+    }
+
+    pub(crate) fn keyword(s: &str, span: Span, tokens: &mut TokenStream) {
+        tokens.append(Ident::new(s, span));
+    }
+
+    pub(crate) fn delim(
+        delim: Delimiter,
+        span: Span,
+        tokens: &mut TokenStream,
+        inner: TokenStream,
+    ) {
+        let mut g = Group::new(delim, inner);
+        g.set_span(span);
+        tokens.append(g);
+    }
+}