Merge tag 'trace-v7.3-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-tracegrafted

Pull tracing fixes from Steven Rostedt:

 - Don't destroy user event fields when removal fails

   User event fields are destroyed before the event is removed from
   visibility. But that can fail leaving the still visible event with no
   fields. Move the destroying of the fields to after the event is
   successfully removed from visibility.

 - Initialize function graph state is fork before calling
   copy_exec_state()

   For non-CLONE_VM forks, copy_exec_state() allocates a new
   task_exec_state. If that allocation fails, ftrace_graph_exit_task()
   will free the tasks ret_stack pointer. Since that pointer is still
   using the parent's ret_stack, it mistakenly frees the parent's
   pointer too.

   Call ftrace_graph_init() on the task first which will NULL out the
   new tasks's ret_stack and if the copy fails, it will not free
   anything.

 - Remove FGRAPH_MAX_INDEX

   The macro FGRAPH_MAX_INDEX was added but never used. Remove it.

 - Save ent_size in function graph printing of nested functions

   The function graph tracer needs to look at the next event to see if
   the next event is the return of the current function entry. If it is,
   it prints a single line:

	ktime_get();

   Otherwise it prints it like a nested function:

	tick_nohz_irq_exit() {
	    ktime_get();
	    kcpustat_irq_exit();
	}

   In order to look at the next event, it must save the current event so
   that it has the information to print from it. It saves the event in
   the iterator descriptor called "ent". What it doesn't save is the
   ent_size of the event which is now used to know if the function graph
   arguments are to be printed. The peek doesn't save the size so the
   size used happens to be that of the size of the last event that was
   seen.

   Save the entry event size in the iterator descriptor so that the
   correct size is used.

 - Fix several errors with freeing data in the histogram code

   The histogram code had a lot of leaked or or incorrect accounting
   when failures happen. Correct them.

 - Fix histogram regression of .percent and .graph modifiers

   Up until 6.3 histogram values could have "percent" or "graph"
   modifiers that changed how they were printed. But a change that added
   restricting histograms values from being strings, stack traces and
   other modifiers inadvertently prevented them from using the percent
   and graph modifiers, which were legal use cases for values.

   Put back the percent and graph modifiers.

 - Fix various typos in the comments

 - Set the trace_clock before initializing a histogram with clock
   argument

   The histogram API allows the user to specific which trace clock to
   use via a "clock=" string. The histogram is set up first before the
   clock is checked. If the passed in clock is not valid, it exits
   without fully fixing up the histogram leaving it on the list and a
   use-after-free can trigger.

   Update the clock argument first and if it fails then exit gracefully
   before the histogram trigger is placed on any lists.

 - Restore :mod: trailer after parsing in ftrace_set_clr_event

   The function ftrace_set_clr_event() modifies the parse string and
   needs to put it back to what was passed in. It searches for ":mod:"
   via a strsep() but fails to put back the first ':' in the string.

   Add back the ':' in the passed in string.

 - Take trace_array reference when opening a tracer options file

   The options files are dynamically created and some tracers add their
   own options. When a tracer adds their own list of options, the
   trace_array holding them has an array to hold the list of options for
   each tracer. This array increases in size via a krealloc(), and the
   new entry gets a newly allocated array to hold the options of the new
   tracer being added.

   The element in each entry of the tracer's option array holds a
   pointer back to the trace_array, a pointer to the tracer it is
   associated to, a pointer to the flags of the option.

   The issue is that these arrays are freed when the trace_array is
   freed when its instance it represents is removed from the instances
   directory. There's a race that an open of one of these options files
   can happen when the instance is being removed.

   Add a new helper function to be called by the open function of the
   options file to iterate all existing trace_arrays under a lock and
   find the one that has the given option element in one of it's tracer
   arrays. If found, then update the associated trace_array's reference
   counter to keep it from being freed. If not found, have the open call
   return -ENODEV.

 - Disable interrupts when acquiring the lock in rb_wake_up_waiters()

   The function rb_wake_up_waiters() assumes it will be called in
   interrupt context and does not disable irqs when taking
   cpu_buffer->reader_lock, which can be called in hard interrupt
   context. The issue is in PREEMPT_RT, this function is called in
   thread context leaving this lock open to a deadlock.

   Take the lock with interrupts disabled.

 - Use rcu_assign_pointer() for tmp_ops filter hash

   The tmp_ops used in update_ftrace_direct_mod() assigns its
   filter_hash field directly, but that field is annotated as __rcu and
   sparse complains. Assign it with rcu_assign_pointer()

 - Fix use-after-free in enable_trigger_private_data_free()

   The trace_event_call is accessed through the event_trigger_data's
   trace_event_file pointer to put the trace_event_call on freeing. The
   issue is that the trace_event_file data may have been freed already
   causing a use-after-free. Add a field to the event_trigger_data that
   points directly to the trace_event_call so that it can decrement its
   reference directly without needing to go through the
   trace_event_file.

 - Fix accounting of buffer data remote headers

   trace_buffer_desc_size() and trace_remote_alloc_buffer() undercount
   the number of pages is needed for the asked for size as it doesn't
   take into account the meta data on each page. Add a helper function
   to do the calculation properly and use that in these functions.

 - Catch nr_page_va overflow in ring_buffer_desc sizing

   The number of pages per remote ring buffer is capped by
   ring_buffer_desc::nr_page_va (32 bits). A buffer_size large enough to
   overflow that field would silently allocate a descriptor smaller than
   what was asked for.

 - Do not resize the subbuf order if any per_cpu buffer is disabled

   The mmapping of ring buffers disables resizing the subbuffers, but it
   is done per-cpu whereas the subbuf size change is done for all the
   per_cpu buffers under the buffer->mutex. It could change the size of
   some while the mapping is happening on others. Have the resize of the
   subbuf order check all the per_cpu buffers under the lock to see if
   any of them is disabled before starting and causing an inconsistency
   between buffers that are being mapped.

* tag 'trace-v7.3-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace: (25 commits)
  ring-buffer: Check resize_disabled before publishing the new subbuf order
  tracing/remotes: Catch nr_page_va overflow in ring_buffer_desc sizing
  tracing/remotes: Account for ring buffer page header in size calculation
  tracing: Don't dereference trace_event_file in deferred trigger free
  ftrace: Use rcu_assign_pointer() for tmp_ops filter hash
  ring-buffer: Acquire the lock with irqsave in rb_wake_up_waiters()
  tracing: Take trace_array reference when opening a tracer options file
  tracing: Fix ring_buffer_read_page_size() kernel-doc
  tracing: Restore :mod: trailer after parsing in ftrace_set_clr_event()
  tracing: Fix memory corruption from a "STACKTRACE" histogram key
  tracing: Fix memory corruption from the histogram stacktrace modifier
  tracing: Undo the registration when enabling the histogram trigger fails
  tracing: Take the reference before publishing the named histogram trigger
  tracing: Set the trace clock before registering the histogram trigger
  tracing: Fix typo "preceeded" in comment
  tracing: Fix typo "availabe" in comment
  tracing: Let histogram values keep the percent and graph modifiers
  tracing: Keep the entry count when the histogram stats allocation fails
  tracing: Free histogram the field rejected for a bad modifier
  tracing: Free histogram the var ref when its initialization fails
  ...

1 files changed, 1157 insertions, 0 deletions

diff --git a/rust/syn/punctuated.rs b/rust/syn/punctuated.rs
new file mode 100644
index 000000000..f79152940
--- /dev/null
+++ b/rust/syn/punctuated.rs
@@ -0,0 +1,1157 @@
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
+//! A punctuated sequence of syntax tree nodes separated by punctuation.
+//!
+//! Lots of things in Rust are punctuated sequences.
+//!
+//! - The fields of a struct are `Punctuated<Field, Token![,]>`.
+//! - The segments of a path are `Punctuated<PathSegment, Token![::]>`.
+//! - The bounds on a generic parameter are `Punctuated<TypeParamBound,
+//!   Token![+]>`.
+//! - The arguments to a function call are `Punctuated<Expr, Token![,]>`.
+//!
+//! This module provides a common representation for these punctuated sequences
+//! in the form of the [`Punctuated<T, P>`] type. We store a vector of pairs of
+//! syntax tree node + punctuation, where every node in the sequence is followed
+//! by punctuation except for possibly the final one.
+//!
+//! [`Punctuated<T, P>`]: Punctuated
+//!
+//! ```text
+//! a_function_call(arg1, arg2, arg3);
+//!                 ~~~~^ ~~~~^ ~~~~
+//! ```
+
+use crate::drops::{NoDrop, TrivialDrop};
+#[cfg(feature = "parsing")]
+use crate::error::Result;
+#[cfg(feature = "parsing")]
+use crate::parse::{Parse, ParseStream};
+#[cfg(feature = "parsing")]
+use crate::token::Token;
+#[cfg(feature = "extra-traits")]
+use std::fmt::{self, Debug};
+#[cfg(feature = "extra-traits")]
+use std::hash::{Hash, Hasher};
+#[cfg(any(feature = "full", feature = "derive"))]
+use std::iter;
+use std::ops::{Index, IndexMut};
+use std::option;
+use std::slice;
+use std::vec;
+
+/// **A punctuated sequence of syntax tree nodes of type `T` separated by
+/// punctuation of type `P`.**
+///
+/// Refer to the [module documentation] for details about punctuated sequences.
+///
+/// [module documentation]: self
+pub struct Punctuated<T, P> {
+    inner: Vec<(T, P)>,
+    last: Option<Box<T>>,
+}
+
+impl<T, P> Punctuated<T, P> {
+    /// Creates an empty punctuated sequence.
+    pub const fn new() -> Self {
+        Punctuated {
+            inner: Vec::new(),
+            last: None,
+        }
+    }
+
+    /// Determines whether this punctuated sequence is empty, meaning it
+    /// contains no syntax tree nodes or punctuation.
+    pub fn is_empty(&self) -> bool {
+        self.inner.len() == 0 && self.last.is_none()
+    }
+
+    /// Returns the number of syntax tree nodes in this punctuated sequence.
+    ///
+    /// This is the number of nodes of type `T`, not counting the punctuation of
+    /// type `P`.
+    pub fn len(&self) -> usize {
+        self.inner.len() + if self.last.is_some() { 1 } else { 0 }
+    }
+
+    /// Borrows the first element in this sequence.
+    pub fn first(&self) -> Option<&T> {
+        self.iter().next()
+    }
+
+    /// Mutably borrows the first element in this sequence.
+    pub fn first_mut(&mut self) -> Option<&mut T> {
+        self.iter_mut().next()
+    }
+
+    /// Borrows the last element in this sequence.
+    pub fn last(&self) -> Option<&T> {
+        self.iter().next_back()
+    }
+
+    /// Mutably borrows the last element in this sequence.
+    pub fn last_mut(&mut self) -> Option<&mut T> {
+        self.iter_mut().next_back()
+    }
+
+    /// Borrows the element at the given index.
+    pub fn get(&self, index: usize) -> Option<&T> {
+        if let Some((value, _punct)) = self.inner.get(index) {
+            Some(value)
+        } else if index == self.inner.len() {
+            self.last.as_deref()
+        } else {
+            None
+        }
+    }
+
+    /// Mutably borrows the element at the given index.
+    pub fn get_mut(&mut self, index: usize) -> Option<&mut T> {
+        let inner_len = self.inner.len();
+        if let Some((value, _punct)) = self.inner.get_mut(index) {
+            Some(value)
+        } else if index == inner_len {
+            self.last.as_deref_mut()
+        } else {
+            None
+        }
+    }
+
+    /// Returns an iterator over borrowed syntax tree nodes of type `&T`.
+    pub fn iter(&self) -> Iter<T> {
+        Iter {
+            inner: Box::new(NoDrop::new(PrivateIter {
+                inner: self.inner.iter(),
+                last: self.last.as_ref().map(Box::as_ref).into_iter(),
+            })),
+        }
+    }
+
+    /// Returns an iterator over mutably borrowed syntax tree nodes of type
+    /// `&mut T`.
+    pub fn iter_mut(&mut self) -> IterMut<T> {
+        IterMut {
+            inner: Box::new(NoDrop::new(PrivateIterMut {
+                inner: self.inner.iter_mut(),
+                last: self.last.as_mut().map(Box::as_mut).into_iter(),
+            })),
+        }
+    }
+
+    /// Returns an iterator over the contents of this sequence as borrowed
+    /// punctuated pairs.
+    pub fn pairs(&self) -> Pairs<T, P> {
+        Pairs {
+            inner: self.inner.iter(),
+            last: self.last.as_ref().map(Box::as_ref).into_iter(),
+        }
+    }
+
+    /// Returns an iterator over the contents of this sequence as mutably
+    /// borrowed punctuated pairs.
+    pub fn pairs_mut(&mut self) -> PairsMut<T, P> {
+        PairsMut {
+            inner: self.inner.iter_mut(),
+            last: self.last.as_mut().map(Box::as_mut).into_iter(),
+        }
+    }
+
+    /// Returns an iterator over the contents of this sequence as owned
+    /// punctuated pairs.
+    pub fn into_pairs(self) -> IntoPairs<T, P> {
+        IntoPairs {
+            inner: self.inner.into_iter(),
+            last: self.last.map(|t| *t).into_iter(),
+        }
+    }
+
+    /// Appends a syntax tree node onto the end of this punctuated sequence. The
+    /// sequence must already have a trailing punctuation, or be empty.
+    ///
+    /// Use [`push`] instead if the punctuated sequence may or may not already
+    /// have trailing punctuation.
+    ///
+    /// [`push`]: Punctuated::push
+    ///
+    /// # Panics
+    ///
+    /// Panics if the sequence is nonempty and does not already have a trailing
+    /// punctuation.
+    pub fn push_value(&mut self, value: T) {
+        assert!(
+            self.empty_or_trailing(),
+            "Punctuated::push_value: cannot push value if Punctuated is missing trailing punctuation",
+        );
+
+        self.last = Some(Box::new(value));
+    }
+
+    /// Appends a trailing punctuation onto the end of this punctuated sequence.
+    /// The sequence must be non-empty and must not already have trailing
+    /// punctuation.
+    ///
+    /// # Panics
+    ///
+    /// Panics if the sequence is empty or already has a trailing punctuation.
+    pub fn push_punct(&mut self, punctuation: P) {
+        assert!(
+            self.last.is_some(),
+            "Punctuated::push_punct: cannot push punctuation if Punctuated is empty or already has trailing punctuation",
+        );
+
+        let last = self.last.take().unwrap();
+        self.inner.push((*last, punctuation));
+    }
+
+    /// Removes the last punctuated pair from this sequence, or `None` if the
+    /// sequence is empty.
+    pub fn pop(&mut self) -> Option<Pair<T, P>> {
+        if self.last.is_some() {
+            self.last.take().map(|t| Pair::End(*t))
+        } else {
+            self.inner.pop().map(|(t, p)| Pair::Punctuated(t, p))
+        }
+    }
+
+    /// Removes the trailing punctuation from this punctuated sequence, or
+    /// `None` if there isn't any.
+    pub fn pop_punct(&mut self) -> Option<P> {
+        if self.last.is_some() {
+            None
+        } else {
+            let (t, p) = self.inner.pop()?;
+            self.last = Some(Box::new(t));
+            Some(p)
+        }
+    }
+
+    /// Determines whether this punctuated sequence ends with a trailing
+    /// punctuation.
+    pub fn trailing_punct(&self) -> bool {
+        self.last.is_none() && !self.is_empty()
+    }
+
+    /// Returns true if either this `Punctuated` is empty, or it has a trailing
+    /// punctuation.
+    ///
+    /// Equivalent to `punctuated.is_empty() || punctuated.trailing_punct()`.
+    pub fn empty_or_trailing(&self) -> bool {
+        self.last.is_none()
+    }
+
+    /// Appends a syntax tree node onto the end of this punctuated sequence.
+    ///
+    /// If there is not a trailing punctuation in this sequence when this method
+    /// is called, the default value of punctuation type `P` is inserted before
+    /// the given value of type `T`.
+    pub fn push(&mut self, value: T)
+    where
+        P: Default,
+    {
+        if !self.empty_or_trailing() {
+            self.push_punct(Default::default());
+        }
+        self.push_value(value);
+    }
+
+    /// Inserts an element at position `index`.
+    ///
+    /// # Panics
+    ///
+    /// Panics if `index` is greater than the number of elements previously in
+    /// this punctuated sequence.
+    pub fn insert(&mut self, index: usize, value: T)
+    where
+        P: Default,
+    {
+        assert!(
+            index <= self.len(),
+            "Punctuated::insert: index out of range",
+        );
+
+        if index == self.len() {
+            self.push(value);
+        } else {
+            self.inner.insert(index, (value, Default::default()));
+        }
+    }
+
+    /// Clears the sequence of all values and punctuation, making it empty.
+    pub fn clear(&mut self) {
+        self.inner.clear();
+        self.last = None;
+    }
+
+    /// Parses zero or more occurrences of `T` separated by punctuation of type
+    /// `P`, with optional trailing punctuation.
+    ///
+    /// Parsing continues until the end of this parse stream. The entire content
+    /// of this parse stream must consist of `T` and `P`.
+    #[cfg(feature = "parsing")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
+    pub fn parse_terminated(input: ParseStream) -> Result<Self>
+    where
+        T: Parse,
+        P: Parse,
+    {
+        Self::parse_terminated_with(input, T::parse)
+    }
+
+    /// Parses zero or more occurrences of `T` using the given parse function,
+    /// separated by punctuation of type `P`, with optional trailing
+    /// punctuation.
+    ///
+    /// Like [`parse_terminated`], the entire content of this stream is expected
+    /// to be parsed.
+    ///
+    /// [`parse_terminated`]: Punctuated::parse_terminated
+    #[cfg(feature = "parsing")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
+    pub fn parse_terminated_with<'a>(
+        input: ParseStream<'a>,
+        parser: fn(ParseStream<'a>) -> Result<T>,
+    ) -> Result<Self>
+    where
+        P: Parse,
+    {
+        let mut punctuated = Punctuated::new();
+
+        loop {
+            if input.is_empty() {
+                break;
+            }
+            let value = parser(input)?;
+            punctuated.push_value(value);
+            if input.is_empty() {
+                break;
+            }
+            let punct = input.parse()?;
+            punctuated.push_punct(punct);
+        }
+
+        Ok(punctuated)
+    }
+
+    /// Parses one or more occurrences of `T` separated by punctuation of type
+    /// `P`, not accepting trailing punctuation.
+    ///
+    /// Parsing continues as long as punctuation `P` is present at the head of
+    /// the stream. This method returns upon parsing a `T` and observing that it
+    /// is not followed by a `P`, even if there are remaining tokens in the
+    /// stream.
+    #[cfg(feature = "parsing")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
+    pub fn parse_separated_nonempty(input: ParseStream) -> Result<Self>
+    where
+        T: Parse,
+        P: Token + Parse,
+    {
+        Self::parse_separated_nonempty_with(input, T::parse)
+    }
+
+    /// Parses one or more occurrences of `T` using the given parse function,
+    /// separated by punctuation of type `P`, not accepting trailing
+    /// punctuation.
+    ///
+    /// Like [`parse_separated_nonempty`], may complete early without parsing
+    /// the entire content of this stream.
+    ///
+    /// [`parse_separated_nonempty`]: Punctuated::parse_separated_nonempty
+    #[cfg(feature = "parsing")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
+    pub fn parse_separated_nonempty_with<'a>(
+        input: ParseStream<'a>,
+        parser: fn(ParseStream<'a>) -> Result<T>,
+    ) -> Result<Self>
+    where
+        P: Token + Parse,
+    {
+        let mut punctuated = Punctuated::new();
+
+        loop {
+            let value = parser(input)?;
+            punctuated.push_value(value);
+            if !P::peek(input.cursor()) {
+                break;
+            }
+            let punct = input.parse()?;
+            punctuated.push_punct(punct);
+        }
+
+        Ok(punctuated)
+    }
+}
+
+#[cfg(feature = "clone-impls")]
+#[cfg_attr(docsrs, doc(cfg(feature = "clone-impls")))]
+impl<T, P> Clone for Punctuated<T, P>
+where
+    T: Clone,
+    P: Clone,
+{
+    fn clone(&self) -> Self {
+        Punctuated {
+            inner: self.inner.clone(),
+            last: self.last.clone(),
+        }
+    }
+
+    fn clone_from(&mut self, other: &Self) {
+        self.inner.clone_from(&other.inner);
+        self.last.clone_from(&other.last);
+    }
+}
+
+#[cfg(feature = "extra-traits")]
+#[cfg_attr(docsrs, doc(cfg(feature = "extra-traits")))]
+impl<T, P> Eq for Punctuated<T, P>
+where
+    T: Eq,
+    P: Eq,
+{
+}
+
+#[cfg(feature = "extra-traits")]
+#[cfg_attr(docsrs, doc(cfg(feature = "extra-traits")))]
+impl<T, P> PartialEq for Punctuated<T, P>
+where
+    T: PartialEq,
+    P: PartialEq,
+{
+    fn eq(&self, other: &Self) -> bool {
+        let Punctuated { inner, last } = self;
+        *inner == other.inner && *last == other.last
+    }
+}
+
+#[cfg(feature = "extra-traits")]
+#[cfg_attr(docsrs, doc(cfg(feature = "extra-traits")))]
+impl<T, P> Hash for Punctuated<T, P>
+where
+    T: Hash,
+    P: Hash,
+{
+    fn hash<H: Hasher>(&self, state: &mut H) {
+        let Punctuated { inner, last } = self;
+        inner.hash(state);
+        last.hash(state);
+    }
+}
+
+#[cfg(feature = "extra-traits")]
+#[cfg_attr(docsrs, doc(cfg(feature = "extra-traits")))]
+impl<T: Debug, P: Debug> Debug for Punctuated<T, P> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        let mut list = f.debug_list();
+        for (t, p) in &self.inner {
+            list.entry(t);
+            list.entry(p);
+        }
+        if let Some(last) = &self.last {
+            list.entry(last);
+        }
+        list.finish()
+    }
+}
+
+impl<T, P> FromIterator<T> for Punctuated<T, P>
+where
+    P: Default,
+{
+    fn from_iter<I: IntoIterator<Item = T>>(i: I) -> Self {
+        let mut ret = Punctuated::new();
+        ret.extend(i);
+        ret
+    }
+}
+
+impl<T, P> Extend<T> for Punctuated<T, P>
+where
+    P: Default,
+{
+    fn extend<I: IntoIterator<Item = T>>(&mut self, i: I) {
+        for value in i {
+            self.push(value);
+        }
+    }
+}
+
+impl<T, P> FromIterator<Pair<T, P>> for Punctuated<T, P> {
+    fn from_iter<I: IntoIterator<Item = Pair<T, P>>>(i: I) -> Self {
+        let mut ret = Punctuated::new();
+        do_extend(&mut ret, i.into_iter());
+        ret
+    }
+}
+
+impl<T, P> Extend<Pair<T, P>> for Punctuated<T, P>
+where
+    P: Default,
+{
+    fn extend<I: IntoIterator<Item = Pair<T, P>>>(&mut self, i: I) {
+        if !self.empty_or_trailing() {
+            self.push_punct(P::default());
+        }
+        do_extend(self, i.into_iter());
+    }
+}
+
+fn do_extend<T, P, I>(punctuated: &mut Punctuated<T, P>, i: I)
+where
+    I: Iterator<Item = Pair<T, P>>,
+{
+    let mut nomore = false;
+    for pair in i {
+        if nomore {
+            panic!("punctuated extended with items after a Pair::End");
+        }
+        match pair {
+            Pair::Punctuated(a, b) => punctuated.inner.push((a, b)),
+            Pair::End(a) => {
+                punctuated.last = Some(Box::new(a));
+                nomore = true;
+            }
+        }
+    }
+}
+
+impl<T, P> IntoIterator for Punctuated<T, P> {
+    type Item = T;
+    type IntoIter = IntoIter<T>;
+
+    fn into_iter(self) -> Self::IntoIter {
+        let mut elements = Vec::with_capacity(self.len());
+        elements.extend(self.inner.into_iter().map(|pair| pair.0));
+        elements.extend(self.last.map(|t| *t));
+
+        IntoIter {
+            inner: elements.into_iter(),
+        }
+    }
+}
+
+impl<'a, T, P> IntoIterator for &'a Punctuated<T, P> {
+    type Item = &'a T;
+    type IntoIter = Iter<'a, T>;
+
+    fn into_iter(self) -> Self::IntoIter {
+        Punctuated::iter(self)
+    }
+}
+
+impl<'a, T, P> IntoIterator for &'a mut Punctuated<T, P> {
+    type Item = &'a mut T;
+    type IntoIter = IterMut<'a, T>;
+
+    fn into_iter(self) -> Self::IntoIter {
+        Punctuated::iter_mut(self)
+    }
+}
+
+impl<T, P> Default for Punctuated<T, P> {
+    fn default() -> Self {
+        Punctuated::new()
+    }
+}
+
+/// An iterator over borrowed pairs of type `Pair<&T, &P>`.
+///
+/// Refer to the [module documentation] for details about punctuated sequences.
+///
+/// [module documentation]: self
+pub struct Pairs<'a, T: 'a, P: 'a> {
+    inner: slice::Iter<'a, (T, P)>,
+    last: option::IntoIter<&'a T>,
+}
+
+impl<'a, T, P> Iterator for Pairs<'a, T, P> {
+    type Item = Pair<&'a T, &'a P>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        self.inner
+            .next()
+            .map(|(t, p)| Pair::Punctuated(t, p))
+            .or_else(|| self.last.next().map(Pair::End))
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        (self.len(), Some(self.len()))
+    }
+}
+
+impl<'a, T, P> DoubleEndedIterator for Pairs<'a, T, P> {
+    fn next_back(&mut self) -> Option<Self::Item> {
+        self.last
+            .next()
+            .map(Pair::End)
+            .or_else(|| self.inner.next_back().map(|(t, p)| Pair::Punctuated(t, p)))
+    }
+}
+
+impl<'a, T, P> ExactSizeIterator for Pairs<'a, T, P> {
+    fn len(&self) -> usize {
+        self.inner.len() + self.last.len()
+    }
+}
+
+// No Clone bound on T or P.
+impl<'a, T, P> Clone for Pairs<'a, T, P> {
+    fn clone(&self) -> Self {
+        Pairs {
+            inner: self.inner.clone(),
+            last: self.last.clone(),
+        }
+    }
+}
+
+/// An iterator over mutably borrowed pairs of type `Pair<&mut T, &mut P>`.
+///
+/// Refer to the [module documentation] for details about punctuated sequences.
+///
+/// [module documentation]: self
+pub struct PairsMut<'a, T: 'a, P: 'a> {
+    inner: slice::IterMut<'a, (T, P)>,
+    last: option::IntoIter<&'a mut T>,
+}
+
+impl<'a, T, P> Iterator for PairsMut<'a, T, P> {
+    type Item = Pair<&'a mut T, &'a mut P>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        self.inner
+            .next()
+            .map(|(t, p)| Pair::Punctuated(t, p))
+            .or_else(|| self.last.next().map(Pair::End))
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        (self.len(), Some(self.len()))
+    }
+}
+
+impl<'a, T, P> DoubleEndedIterator for PairsMut<'a, T, P> {
+    fn next_back(&mut self) -> Option<Self::Item> {
+        self.last
+            .next()
+            .map(Pair::End)
+            .or_else(|| self.inner.next_back().map(|(t, p)| Pair::Punctuated(t, p)))
+    }
+}
+
+impl<'a, T, P> ExactSizeIterator for PairsMut<'a, T, P> {
+    fn len(&self) -> usize {
+        self.inner.len() + self.last.len()
+    }
+}
+
+/// An iterator over owned pairs of type `Pair<T, P>`.
+///
+/// Refer to the [module documentation] for details about punctuated sequences.
+///
+/// [module documentation]: self
+pub struct IntoPairs<T, P> {
+    inner: vec::IntoIter<(T, P)>,
+    last: option::IntoIter<T>,
+}
+
+impl<T, P> Iterator for IntoPairs<T, P> {
+    type Item = Pair<T, P>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        self.inner
+            .next()
+            .map(|(t, p)| Pair::Punctuated(t, p))
+            .or_else(|| self.last.next().map(Pair::End))
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        (self.len(), Some(self.len()))
+    }
+}
+
+impl<T, P> DoubleEndedIterator for IntoPairs<T, P> {
+    fn next_back(&mut self) -> Option<Self::Item> {
+        self.last
+            .next()
+            .map(Pair::End)
+            .or_else(|| self.inner.next_back().map(|(t, p)| Pair::Punctuated(t, p)))
+    }
+}
+
+impl<T, P> ExactSizeIterator for IntoPairs<T, P> {
+    fn len(&self) -> usize {
+        self.inner.len() + self.last.len()
+    }
+}
+
+impl<T, P> Clone for IntoPairs<T, P>
+where
+    T: Clone,
+    P: Clone,
+{
+    fn clone(&self) -> Self {
+        IntoPairs {
+            inner: self.inner.clone(),
+            last: self.last.clone(),
+        }
+    }
+}
+
+/// An iterator over owned values of type `T`.
+///
+/// Refer to the [module documentation] for details about punctuated sequences.
+///
+/// [module documentation]: self
+pub struct IntoIter<T> {
+    inner: vec::IntoIter<T>,
+}
+
+impl<T> Iterator for IntoIter<T> {
+    type Item = T;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        self.inner.next()
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        (self.len(), Some(self.len()))
+    }
+}
+
+impl<T> DoubleEndedIterator for IntoIter<T> {
+    fn next_back(&mut self) -> Option<Self::Item> {
+        self.inner.next_back()
+    }
+}
+
+impl<T> ExactSizeIterator for IntoIter<T> {
+    fn len(&self) -> usize {
+        self.inner.len()
+    }
+}
+
+impl<T> Clone for IntoIter<T>
+where
+    T: Clone,
+{
+    fn clone(&self) -> Self {
+        IntoIter {
+            inner: self.inner.clone(),
+        }
+    }
+}
+
+/// An iterator over borrowed values of type `&T`.
+///
+/// Refer to the [module documentation] for details about punctuated sequences.
+///
+/// [module documentation]: self
+pub struct Iter<'a, T: 'a> {
+    inner: Box<NoDrop<dyn IterTrait<'a, T> + 'a>>,
+}
+
+trait IterTrait<'a, T: 'a>: Iterator<Item = &'a T> + DoubleEndedIterator + ExactSizeIterator {
+    fn clone_box(&self) -> Box<NoDrop<dyn IterTrait<'a, T> + 'a>>;
+}
+
+struct PrivateIter<'a, T: 'a, P: 'a> {
+    inner: slice::Iter<'a, (T, P)>,
+    last: option::IntoIter<&'a T>,
+}
+
+impl<'a, T, P> TrivialDrop for PrivateIter<'a, T, P>
+where
+    slice::Iter<'a, (T, P)>: TrivialDrop,
+    option::IntoIter<&'a T>: TrivialDrop,
+{
+}
+
+#[cfg(any(feature = "full", feature = "derive"))]
+pub(crate) fn empty_punctuated_iter<'a, T>() -> Iter<'a, T> {
+    Iter {
+        inner: Box::new(NoDrop::new(iter::empty())),
+    }
+}
+
+// No Clone bound on T.
+impl<'a, T> Clone for Iter<'a, T> {
+    fn clone(&self) -> Self {
+        Iter {
+            inner: self.inner.clone_box(),
+        }
+    }
+}
+
+impl<'a, T> Iterator for Iter<'a, T> {
+    type Item = &'a T;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        self.inner.next()
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        (self.len(), Some(self.len()))
+    }
+}
+
+impl<'a, T> DoubleEndedIterator for Iter<'a, T> {
+    fn next_back(&mut self) -> Option<Self::Item> {
+        self.inner.next_back()
+    }
+}
+
+impl<'a, T> ExactSizeIterator for Iter<'a, T> {
+    fn len(&self) -> usize {
+        self.inner.len()
+    }
+}
+
+impl<'a, T, P> Iterator for PrivateIter<'a, T, P> {
+    type Item = &'a T;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        self.inner
+            .next()
+            .map(|pair| &pair.0)
+            .or_else(|| self.last.next())
+    }
+}
+
+impl<'a, T, P> DoubleEndedIterator for PrivateIter<'a, T, P> {
+    fn next_back(&mut self) -> Option<Self::Item> {
+        self.last
+            .next()
+            .or_else(|| self.inner.next_back().map(|pair| &pair.0))
+    }
+}
+
+impl<'a, T, P> ExactSizeIterator for PrivateIter<'a, T, P> {
+    fn len(&self) -> usize {
+        self.inner.len() + self.last.len()
+    }
+}
+
+// No Clone bound on T or P.
+impl<'a, T, P> Clone for PrivateIter<'a, T, P> {
+    fn clone(&self) -> Self {
+        PrivateIter {
+            inner: self.inner.clone(),
+            last: self.last.clone(),
+        }
+    }
+}
+
+impl<'a, T, I> IterTrait<'a, T> for I
+where
+    T: 'a,
+    I: DoubleEndedIterator<Item = &'a T>
+        + ExactSizeIterator<Item = &'a T>
+        + Clone
+        + TrivialDrop
+        + 'a,
+{
+    fn clone_box(&self) -> Box<NoDrop<dyn IterTrait<'a, T> + 'a>> {
+        Box::new(NoDrop::new(self.clone()))
+    }
+}
+
+/// An iterator over mutably borrowed values of type `&mut T`.
+///
+/// Refer to the [module documentation] for details about punctuated sequences.
+///
+/// [module documentation]: self
+pub struct IterMut<'a, T: 'a> {
+    inner: Box<NoDrop<dyn IterMutTrait<'a, T, Item = &'a mut T> + 'a>>,
+}
+
+trait IterMutTrait<'a, T: 'a>:
+    DoubleEndedIterator<Item = &'a mut T> + ExactSizeIterator<Item = &'a mut T>
+{
+}
+
+struct PrivateIterMut<'a, T: 'a, P: 'a> {
+    inner: slice::IterMut<'a, (T, P)>,
+    last: option::IntoIter<&'a mut T>,
+}
+
+impl<'a, T, P> TrivialDrop for PrivateIterMut<'a, T, P>
+where
+    slice::IterMut<'a, (T, P)>: TrivialDrop,
+    option::IntoIter<&'a mut T>: TrivialDrop,
+{
+}
+
+#[cfg(any(feature = "full", feature = "derive"))]
+pub(crate) fn empty_punctuated_iter_mut<'a, T>() -> IterMut<'a, T> {
+    IterMut {
+        inner: Box::new(NoDrop::new(iter::empty())),
+    }
+}
+
+impl<'a, T> Iterator for IterMut<'a, T> {
+    type Item = &'a mut T;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        self.inner.next()
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        (self.len(), Some(self.len()))
+    }
+}
+
+impl<'a, T> DoubleEndedIterator for IterMut<'a, T> {
+    fn next_back(&mut self) -> Option<Self::Item> {
+        self.inner.next_back()
+    }
+}
+
+impl<'a, T> ExactSizeIterator for IterMut<'a, T> {
+    fn len(&self) -> usize {
+        self.inner.len()
+    }
+}
+
+impl<'a, T, P> Iterator for PrivateIterMut<'a, T, P> {
+    type Item = &'a mut T;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        self.inner
+            .next()
+            .map(|pair| &mut pair.0)
+            .or_else(|| self.last.next())
+    }
+}
+
+impl<'a, T, P> DoubleEndedIterator for PrivateIterMut<'a, T, P> {
+    fn next_back(&mut self) -> Option<Self::Item> {
+        self.last
+            .next()
+            .or_else(|| self.inner.next_back().map(|pair| &mut pair.0))
+    }
+}
+
+impl<'a, T, P> ExactSizeIterator for PrivateIterMut<'a, T, P> {
+    fn len(&self) -> usize {
+        self.inner.len() + self.last.len()
+    }
+}
+
+impl<'a, T, I> IterMutTrait<'a, T> for I
+where
+    T: 'a,
+    I: DoubleEndedIterator<Item = &'a mut T> + ExactSizeIterator<Item = &'a mut T> + 'a,
+{
+}
+
+/// A single syntax tree node of type `T` followed by its trailing punctuation
+/// of type `P` if any.
+///
+/// Refer to the [module documentation] for details about punctuated sequences.
+///
+/// [module documentation]: self
+pub enum Pair<T, P> {
+    Punctuated(T, P),
+    End(T),
+}
+
+impl<T, P> Pair<T, P> {
+    /// Extracts the syntax tree node from this punctuated pair, discarding the
+    /// following punctuation.
+    pub fn into_value(self) -> T {
+        match self {
+            Pair::Punctuated(t, _) | Pair::End(t) => t,
+        }
+    }
+
+    /// Borrows the syntax tree node from this punctuated pair.
+    pub fn value(&self) -> &T {
+        match self {
+            Pair::Punctuated(t, _) | Pair::End(t) => t,
+        }
+    }
+
+    /// Mutably borrows the syntax tree node from this punctuated pair.
+    pub fn value_mut(&mut self) -> &mut T {
+        match self {
+            Pair::Punctuated(t, _) | Pair::End(t) => t,
+        }
+    }
+
+    /// Borrows the punctuation from this punctuated pair, unless this pair is
+    /// the final one and there is no trailing punctuation.
+    pub fn punct(&self) -> Option<&P> {
+        match self {
+            Pair::Punctuated(_, p) => Some(p),
+            Pair::End(_) => None,
+        }
+    }
+
+    /// Mutably borrows the punctuation from this punctuated pair, unless the
+    /// pair is the final one and there is no trailing punctuation.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// # use proc_macro2::Span;
+    /// # use syn::punctuated::Punctuated;
+    /// # use syn::{parse_quote, Token, TypeParamBound};
+    /// #
+    /// # let mut punctuated = Punctuated::<TypeParamBound, Token![+]>::new();
+    /// # let span = Span::call_site();
+    /// #
+    /// punctuated.insert(0, parse_quote!('lifetime));
+    /// if let Some(punct) = punctuated.pairs_mut().next().unwrap().punct_mut() {
+    ///     punct.span = span;
+    /// }
+    /// ```
+    pub fn punct_mut(&mut self) -> Option<&mut P> {
+        match self {
+            Pair::Punctuated(_, p) => Some(p),
+            Pair::End(_) => None,
+        }
+    }
+
+    /// Creates a punctuated pair out of a syntax tree node and an optional
+    /// following punctuation.
+    pub fn new(t: T, p: Option<P>) -> Self {
+        match p {
+            Some(p) => Pair::Punctuated(t, p),
+            None => Pair::End(t),
+        }
+    }
+
+    /// Produces this punctuated pair as a tuple of syntax tree node and
+    /// optional following punctuation.
+    pub fn into_tuple(self) -> (T, Option<P>) {
+        match self {
+            Pair::Punctuated(t, p) => (t, Some(p)),
+            Pair::End(t) => (t, None),
+        }
+    }
+}
+
+#[cfg(feature = "clone-impls")]
+#[cfg_attr(docsrs, doc(cfg(feature = "clone-impls")))]
+impl<T, P> Pair<&T, &P> {
+    pub fn cloned(self) -> Pair<T, P>
+    where
+        T: Clone,
+        P: Clone,
+    {
+        match self {
+            Pair::Punctuated(t, p) => Pair::Punctuated(t.clone(), p.clone()),
+            Pair::End(t) => Pair::End(t.clone()),
+        }
+    }
+}
+
+#[cfg(feature = "clone-impls")]
+#[cfg_attr(docsrs, doc(cfg(feature = "clone-impls")))]
+impl<T, P> Clone for Pair<T, P>
+where
+    T: Clone,
+    P: Clone,
+{
+    fn clone(&self) -> Self {
+        match self {
+            Pair::Punctuated(t, p) => Pair::Punctuated(t.clone(), p.clone()),
+            Pair::End(t) => Pair::End(t.clone()),
+        }
+    }
+}
+
+#[cfg(feature = "clone-impls")]
+#[cfg_attr(docsrs, doc(cfg(feature = "clone-impls")))]
+impl<T, P> Copy for Pair<T, P>
+where
+    T: Copy,
+    P: Copy,
+{
+}
+
+impl<T, P> Index<usize> for Punctuated<T, P> {
+    type Output = T;
+
+    fn index(&self, index: usize) -> &Self::Output {
+        if index == self.len() - 1 {
+            match &self.last {
+                Some(t) => t,
+                None => &self.inner[index].0,
+            }
+        } else {
+            &self.inner[index].0
+        }
+    }
+}
+
+impl<T, P> IndexMut<usize> for Punctuated<T, P> {
+    fn index_mut(&mut self, index: usize) -> &mut Self::Output {
+        if index == self.len() - 1 {
+            match &mut self.last {
+                Some(t) => t,
+                None => &mut self.inner[index].0,
+            }
+        } else {
+            &mut self.inner[index].0
+        }
+    }
+}
+
+#[cfg(all(feature = "fold", any(feature = "full", feature = "derive")))]
+pub(crate) fn fold<T, P, V, F>(
+    punctuated: Punctuated<T, P>,
+    fold: &mut V,
+    mut f: F,
+) -> Punctuated<T, P>
+where
+    V: ?Sized,
+    F: FnMut(&mut V, T) -> T,
+{
+    Punctuated {
+        inner: punctuated
+            .inner
+            .into_iter()
+            .map(|(t, p)| (f(fold, t), p))
+            .collect(),
+        last: match punctuated.last {
+            Some(t) => Some(Box::new(f(fold, *t))),
+            None => None,
+        },
+    }
+}
+
+#[cfg(feature = "printing")]
+mod printing {
+    use crate::punctuated::{Pair, Punctuated};
+    use proc_macro2::TokenStream;
+    use quote::{ToTokens, TokenStreamExt};
+
+    #[cfg_attr(docsrs, doc(cfg(feature = "printing")))]
+    impl<T, P> ToTokens for Punctuated<T, P>
+    where
+        T: ToTokens,
+        P: ToTokens,
+    {
+        fn to_tokens(&self, tokens: &mut TokenStream) {
+            tokens.append_all(self.pairs());
+        }
+    }
+
+    #[cfg_attr(docsrs, doc(cfg(feature = "printing")))]
+    impl<T, P> ToTokens for Pair<T, P>
+    where
+        T: ToTokens,
+        P: ToTokens,
+    {
+        fn to_tokens(&self, tokens: &mut TokenStream) {
+            match self {
+                Pair::Punctuated(a, b) => {
+                    a.to_tokens(tokens);
+                    b.to_tokens(tokens);
+                }
+                Pair::End(a) => a.to_tokens(tokens),
+            }
+        }
+    }
+}