Update subtree/library to 2025-06-17

alloc/src/collections/btree/set.rs

@@ -1220,11 +1220,11 @@ impl<T, A: Allocator + Clone> BTreeSet<T, A> {
     /// assert_eq!(high.into_iter().collect::<Vec<_>>(), [4, 5, 6, 7]);
     /// ```
     #[unstable(feature = "btree_extract_if", issue = "70530")]
-    pub fn extract_if<'a, F, R>(&'a mut self, range: R, pred: F) -> ExtractIf<'a, T, R, F, A>
+    pub fn extract_if<F, R>(&mut self, range: R, pred: F) -> ExtractIf<'_, T, R, F, A>
     where
         T: Ord,
         R: RangeBounds<T>,
-        F: 'a + FnMut(&T) -> bool,
+        F: FnMut(&T) -> bool,
     {
         let (inner, alloc) = self.map.extract_if_inner(range);
         ExtractIf { pred, inner, alloc }
@@ -1585,11 +1585,11 @@ where
 }
 
 #[unstable(feature = "btree_extract_if", issue = "70530")]
-impl<'a, T, R, F, A: Allocator + Clone> Iterator for ExtractIf<'_, T, R, F, A>
+impl<T, R, F, A: Allocator + Clone> Iterator for ExtractIf<'_, T, R, F, A>
 where
     T: PartialOrd,
     R: RangeBounds<T>,
-    F: 'a + FnMut(&T) -> bool,
+    F: FnMut(&T) -> bool,
 {
     type Item = T;
 

alloc/src/ffi/c_str.rs

@@ -714,6 +714,8 @@ impl ops::Deref for CString {
     }
 }
 
+/// Delegates to the [`CStr`] implementation of [`fmt::Debug`],
+/// showing invalid UTF-8 as hex escapes.
 #[stable(feature = "rust1", since = "1.0.0")]
 impl fmt::Debug for CString {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {

alloc/src/vec/mod.rs

@@ -109,6 +109,11 @@ mod in_place_collect;
 
 mod partial_eq;
 
+#[unstable(feature = "vec_peek_mut", issue = "122742")]
+pub use self::peek_mut::PeekMut;
+
+mod peek_mut;
+
 #[cfg(not(no_global_oom_handling))]
 use self::spec_from_elem::SpecFromElem;
 
@@ -729,6 +734,33 @@ impl<T> Vec<T> {
     pub unsafe fn from_parts(ptr: NonNull<T>, length: usize, capacity: usize) -> Self {
         unsafe { Self::from_parts_in(ptr, length, capacity, Global) }
     }
+
+    /// Returns a mutable reference to the last item in the vector, or
+    /// `None` if it is empty.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// #![feature(vec_peek_mut)]
+    /// let mut vec = Vec::new();
+    /// assert!(vec.peek_mut().is_none());
+    ///
+    /// vec.push(1);
+    /// vec.push(5);
+    /// vec.push(2);
+    /// assert_eq!(vec.last(), Some(&2));
+    /// if let Some(mut val) = vec.peek_mut() {
+    ///     *val = 0;
+    /// }
+    /// assert_eq!(vec.last(), Some(&0));
+    /// ```
+    #[inline]
+    #[unstable(feature = "vec_peek_mut", issue = "122742")]
+    pub fn peek_mut(&mut self) -> Option<PeekMut<'_, T>> {
+        PeekMut::new(self)
+    }
 }
 
 impl<T, A: Allocator> Vec<T, A> {

alloc/src/vec/peek_mut.rs

@@ -0,0 +1,55 @@
+use core::ops::{Deref, DerefMut};
+
+use super::Vec;
+use crate::fmt;
+
+/// Structure wrapping a mutable reference to the last item in a
+/// `Vec`.
+///
+/// This `struct` is created by the [`peek_mut`] method on [`Vec`]. See
+/// its documentation for more.
+///
+/// [`peek_mut`]: Vec::peek_mut
+#[unstable(feature = "vec_peek_mut", issue = "122742")]
+pub struct PeekMut<'a, T> {
+    vec: &'a mut Vec<T>,
+}
+
+#[unstable(feature = "vec_peek_mut", issue = "122742")]
+impl<T: fmt::Debug> fmt::Debug for PeekMut<'_, T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_tuple("PeekMut").field(self.deref()).finish()
+    }
+}
+
+impl<'a, T> PeekMut<'a, T> {
+    pub(crate) fn new(vec: &'a mut Vec<T>) -> Option<Self> {
+        if vec.is_empty() { None } else { Some(Self { vec }) }
+    }
+
+    /// Removes the peeked value from the vector and returns it.
+    #[unstable(feature = "vec_peek_mut", issue = "122742")]
+    pub fn pop(self) -> T {
+        // SAFETY: PeekMut is only constructed if the vec is non-empty
+        unsafe { self.vec.pop().unwrap_unchecked() }
+    }
+}
+
+#[unstable(feature = "vec_peek_mut", issue = "122742")]
+impl<'a, T> Deref for PeekMut<'a, T> {
+    type Target = T;
+
+    fn deref(&self) -> &Self::Target {
+        // SAFETY: PeekMut is only constructed if the vec is non-empty
+        unsafe { self.vec.get_unchecked(self.vec.len() - 1) }
+    }
+}
+
+#[unstable(feature = "vec_peek_mut", issue = "122742")]
+impl<'a, T> DerefMut for PeekMut<'a, T> {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        let idx = self.vec.len() - 1;
+        // SAFETY: PeekMut is only constructed if the vec is non-empty
+        unsafe { self.vec.get_unchecked_mut(idx) }
+    }
+}

alloctests/tests/lib.rs

@@ -40,6 +40,7 @@
 #![feature(vec_deque_truncate_front)]
 #![feature(unique_rc_arc)]
 #![feature(macro_metavar_expr_concat)]
+#![feature(vec_peek_mut)]
 #![allow(internal_features)]
 #![deny(fuzzy_provenance_casts)]
 #![deny(unsafe_op_in_unsafe_fn)]

alloctests/tests/slice.rs

@@ -1636,6 +1636,19 @@ fn test_chunk_by() {
     assert_eq!(iter.next_back(), Some(&[1][..]));
     assert_eq!(iter.next(), Some(&[2, 2, 2][..]));
     assert_eq!(iter.next_back(), None);
+
+    let mut iter = slice.chunk_by(|a, b| a == b);
+    assert_eq!(iter.next(), Some(&[1, 1, 1][..]));
+    assert_eq!(iter.next(), Some(&[3, 3][..]));
+    let mut iter_clone = iter.clone();
+    assert_eq!(iter.next(), Some(&[2, 2, 2][..]));
+    assert_eq!(iter.next(), Some(&[1][..]));
+    assert_eq!(iter.next(), Some(&[0][..]));
+    assert_eq!(iter.next(), None);
+    assert_eq!(iter_clone.next(), Some(&[2, 2, 2][..]));
+    assert_eq!(iter_clone.next(), Some(&[1][..]));
+    assert_eq!(iter_clone.next(), Some(&[0][..]));
+    assert_eq!(iter_clone.next(), None);
 }
 
 #[test]

alloctests/tests/vec.rs

@@ -2698,6 +2698,23 @@ fn test_pop_if_mutates() {
     assert_eq!(v, [2]);
 }
 
+#[test]
+fn test_peek_mut() {
+    let mut vec = Vec::new();
+    assert!(vec.peek_mut().is_none());
+    vec.push(1);
+    vec.push(2);
+    if let Some(mut p) = vec.peek_mut() {
+        assert_eq!(*p, 2);
+        *p = 0;
+        assert_eq!(*p, 0);
+        p.pop();
+        assert_eq!(vec.len(), 1);
+    } else {
+        unreachable!()
+    }
+}
+
 /// This assortment of tests, in combination with miri, verifies we handle UB on fishy arguments
 /// in the stdlib. Draining and extending the allocation are fairly well-tested earlier, but
 /// `vec.insert(usize::MAX, val)` once slipped by!