Merge pull request #18746 from lnicola/sync-from-rust

minor: Sync from downstream

2 files changed, 82 insertions, 57 deletions

diff --git a/library/alloc/src/vec/extract_if.rs b/library/alloc/src/vec/extract_if.rs
index 72d51e89044..4db13981596 100644
--- a/library/alloc/src/vec/extract_if.rs
+++ b/library/alloc/src/vec/extract_if.rs
@@ -1,3 +1,4 @@
+use core::ops::{Range, RangeBounds};
 use core::{ptr, slice};
 
 use super::Vec;
@@ -14,7 +15,7 @@ use crate::alloc::{Allocator, Global};
 /// #![feature(extract_if)]
 ///
 /// let mut v = vec![0, 1, 2];
-/// let iter: std::vec::ExtractIf<'_, _, _> = v.extract_if(|x| *x % 2 == 0);
+/// let iter: std::vec::ExtractIf<'_, _, _> = v.extract_if(.., |x| *x % 2 == 0);
 /// ```
 #[unstable(feature = "extract_if", reason = "recently added", issue = "43244")]
 #[derive(Debug)]
@@ -24,24 +25,32 @@ pub struct ExtractIf<
     T,
     F,
     #[unstable(feature = "allocator_api", issue = "32838")] A: Allocator = Global,
-> where
-    F: FnMut(&mut T) -> bool,
-{
-    pub(super) vec: &'a mut Vec<T, A>,
+> {
+    vec: &'a mut Vec<T, A>,
     /// The index of the item that will be inspected by the next call to `next`.
-    pub(super) idx: usize,
+    idx: usize,
+    /// Elements at and beyond this point will be retained. Must be equal or smaller than `old_len`.
+    end: usize,
     /// The number of items that have been drained (removed) thus far.
-    pub(super) del: usize,
+    del: usize,
     /// The original length of `vec` prior to draining.
-    pub(super) old_len: usize,
+    old_len: usize,
     /// The filter test predicate.
-    pub(super) pred: F,
+    pred: F,
 }
 
-impl<T, F, A: Allocator> ExtractIf<'_, T, F, A>
-where
-    F: FnMut(&mut T) -> bool,
-{
+impl<'a, T, F, A: Allocator> ExtractIf<'a, T, F, A> {
+    pub(super) fn new<R: RangeBounds<usize>>(vec: &'a mut Vec<T, A>, pred: F, range: R) -> Self {
+        let old_len = vec.len();
+        let Range { start, end } = slice::range(range, ..old_len);
+
+        // Guard against the vec getting leaked (leak amplification)
+        unsafe {
+            vec.set_len(0);
+        }
+        ExtractIf { vec, idx: start, del: 0, end, old_len, pred }
+    }
+
     /// Returns a reference to the underlying allocator.
     #[unstable(feature = "allocator_api", issue = "32838")]
     #[inline]
@@ -59,7 +68,7 @@ where
 
     fn next(&mut self) -> Option<T> {
         unsafe {
-            while self.idx < self.old_len {
+            while self.idx < self.end {
                 let i = self.idx;
                 let v = slice::from_raw_parts_mut(self.vec.as_mut_ptr(), self.old_len);
                 let drained = (self.pred)(&mut v[i]);
@@ -82,24 +91,15 @@ where
     }
 
     fn size_hint(&self) -> (usize, Option<usize>) {
-        (0, Some(self.old_len - self.idx))
+        (0, Some(self.end - self.idx))
     }
 }
 
 #[unstable(feature = "extract_if", reason = "recently added", issue = "43244")]
-impl<T, F, A: Allocator> Drop for ExtractIf<'_, T, F, A>
-where
-    F: FnMut(&mut T) -> bool,
-{
+impl<T, F, A: Allocator> Drop for ExtractIf<'_, T, F, A> {
     fn drop(&mut self) {
         unsafe {
             if self.idx < self.old_len && self.del > 0 {
-                // This is a pretty messed up state, and there isn't really an
-                // obviously right thing to do. We don't want to keep trying
-                // to execute `pred`, so we just backshift all the unprocessed
-                // elements and tell the vec that they still exist. The backshift
-                // is required to prevent a double-drop of the last successfully
-                // drained item prior to a panic in the predicate.
                 let ptr = self.vec.as_mut_ptr();
                 let src = ptr.add(self.idx);
                 let dst = src.sub(self.del);
diff --git a/library/alloc/src/vec/mod.rs b/library/alloc/src/vec/mod.rs
index 457be3ae77f..3a706d5f36b 100644
--- a/library/alloc/src/vec/mod.rs
+++ b/library/alloc/src/vec/mod.rs
@@ -56,7 +56,6 @@
 #[cfg(not(no_global_oom_handling))]
 use core::cmp;
 use core::cmp::Ordering;
-use core::fmt;
 use core::hash::{Hash, Hasher};
 #[cfg(not(no_global_oom_handling))]
 use core::iter;
@@ -65,6 +64,7 @@ use core::mem::{self, ManuallyDrop, MaybeUninit, SizedTypeProperties};
 use core::ops::{self, Index, IndexMut, Range, RangeBounds};
 use core::ptr::{self, NonNull};
 use core::slice::{self, SliceIndex};
+use core::{fmt, intrinsics};
 
 #[unstable(feature = "extract_if", reason = "recently added", issue = "43244")]
 pub use self::extract_if::ExtractIf;
@@ -1824,7 +1824,10 @@ impl<T, A: Allocator> Vec<T, A> {
     ///
     /// # Examples
     ///
-    /// This method can be useful for situations in which the vector
+    /// See [`spare_capacity_mut()`] for an example with safe
+    /// initialization of capacity elements and use of this method.
+    ///
+    /// `set_len()` can be useful for situations in which the vector
     /// is serving as a buffer for other code, particularly over FFI:
     ///
     /// ```no_run
@@ -1884,6 +1887,8 @@ impl<T, A: Allocator> Vec<T, A> {
     ///
     /// Normally, here, one would use [`clear`] instead to correctly drop
     /// the contents and thus not leak memory.
+    ///
+    /// [`spare_capacity_mut()`]: Vec::spare_capacity_mut
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     pub unsafe fn set_len(&mut self, new_len: usize) {
@@ -1953,11 +1958,11 @@ impl<T, A: Allocator> Vec<T, A> {
     /// # Examples
     ///
     /// ```
-    /// let mut vec = vec![1, 2, 3];
-    /// vec.insert(1, 4);
-    /// assert_eq!(vec, [1, 4, 2, 3]);
-    /// vec.insert(4, 5);
-    /// assert_eq!(vec, [1, 4, 2, 3, 5]);
+    /// let mut vec = vec!['a', 'b', 'c'];
+    /// vec.insert(1, 'd');
+    /// assert_eq!(vec, ['a', 'd', 'b', 'c']);
+    /// vec.insert(4, 'e');
+    /// assert_eq!(vec, ['a', 'd', 'b', 'c', 'e']);
     /// ```
     ///
     /// # Time complexity
@@ -2024,9 +2029,9 @@ impl<T, A: Allocator> Vec<T, A> {
     /// # Examples
     ///
     /// ```
-    /// let mut v = vec![1, 2, 3];
-    /// assert_eq!(v.remove(1), 2);
-    /// assert_eq!(v, [1, 3]);
+    /// let mut v = vec!['a', 'b', 'c'];
+    /// assert_eq!(v.remove(1), 'b');
+    /// assert_eq!(v, ['a', 'c']);
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     #[track_caller]
@@ -2675,7 +2680,14 @@ impl<T, A: Allocator> Vec<T, A> {
     #[rustc_const_unstable(feature = "const_vec_string_slice", issue = "129041")]
     #[rustc_confusables("length", "size")]
     pub const fn len(&self) -> usize {
-        self.len
+        let len = self.len;
+
+        // SAFETY: The maximum capacity of `Vec<T>` is `isize::MAX` bytes, so the maximum value can
+        // be returned is `usize::checked_div(mem::size_of::<T>()).unwrap_or(usize::MAX)`, which
+        // matches the definition of `T::MAX_SLICE_LEN`.
+        unsafe { intrinsics::assume(len <= T::MAX_SLICE_LEN) };
+
+        len
     }
 
     /// Returns `true` if the vector contains no elements.
@@ -2715,10 +2727,10 @@ impl<T, A: Allocator> Vec<T, A> {
     /// # Examples
     ///
     /// ```
-    /// let mut vec = vec![1, 2, 3];
+    /// let mut vec = vec!['a', 'b', 'c'];
     /// let vec2 = vec.split_off(1);
-    /// assert_eq!(vec, [1]);
-    /// assert_eq!(vec2, [2, 3]);
+    /// assert_eq!(vec, ['a']);
+    /// assert_eq!(vec2, ['b', 'c']);
     /// ```
     #[cfg(not(no_global_oom_handling))]
     #[inline]
@@ -2982,9 +2994,9 @@ impl<T: Clone, A: Allocator> Vec<T, A> {
     /// vec.resize(3, "world");
     /// assert_eq!(vec, ["hello", "world", "world"]);
     ///
-    /// let mut vec = vec![1, 2, 3, 4];
-    /// vec.resize(2, 0);
-    /// assert_eq!(vec, [1, 2]);
+    /// let mut vec = vec!['a', 'b', 'c', 'd'];
+    /// vec.resize(2, '_');
+    /// assert_eq!(vec, ['a', 'b']);
     /// ```
     #[cfg(not(no_global_oom_handling))]
     #[stable(feature = "vec_resize", since = "1.5.0")]
@@ -3615,12 +3627,15 @@ impl<T, A: Allocator> Vec<T, A> {
         Splice { drain: self.drain(range), replace_with: replace_with.into_iter() }
     }
 
-    /// Creates an iterator which uses a closure to determine if an element should be removed.
+    /// Creates an iterator which uses a closure to determine if element in the range should be removed.
     ///
     /// If the closure returns true, then the element is removed and yielded.
     /// If the closure returns false, the element will remain in the vector and will not be yielded
     /// by the iterator.
     ///
+    /// Only elements that fall in the provided range are considered for extraction, but any elements
+    /// after the range will still have to be moved if any element has been extracted.
+    ///
     /// If the returned `ExtractIf` is not exhausted, e.g. because it is dropped without iterating
     /// or the iteration short-circuits, then the remaining elements will be retained.
     /// Use [`retain`] with a negated predicate if you do not need the returned iterator.
@@ -3630,10 +3645,12 @@ impl<T, A: Allocator> Vec<T, A> {
     /// Using this method is equivalent to the following code:
     ///
     /// ```
+    /// # use std::cmp::min;
     /// # let some_predicate = |x: &mut i32| { *x == 2 || *x == 3 || *x == 6 };
     /// # let mut vec = vec![1, 2, 3, 4, 5, 6];
-    /// let mut i = 0;
-    /// while i < vec.len() {
+    /// # let range = 1..4;
+    /// let mut i = range.start;
+    /// while i < min(vec.len(), range.end) {
     ///     if some_predicate(&mut vec[i]) {
     ///         let val = vec.remove(i);
     ///         // your code here
@@ -3648,8 +3665,12 @@ impl<T, A: Allocator> Vec<T, A> {
     /// But `extract_if` is easier to use. `extract_if` is also more efficient,
     /// because it can backshift the elements of the array in bulk.
     ///
-    /// Note that `extract_if` also lets you mutate every element in the filter closure,
-    /// regardless of whether you choose to keep or remove it.
+    /// Note that `extract_if` also lets you mutate the elements passed to the filter closure,
+    /// regardless of whether you choose to keep or remove them.
+    ///
+    /// # Panics
+    ///
+    /// If `range` is out of bounds.
     ///
     /// # Examples
     ///
@@ -3659,25 +3680,29 @@ impl<T, A: Allocator> Vec<T, A> {
     /// #![feature(extract_if)]
     /// let mut numbers = vec![1, 2, 3, 4, 5, 6, 8, 9, 11, 13, 14, 15];
     ///
-    /// let evens = numbers.extract_if(|x| *x % 2 == 0).collect::<Vec<_>>();
+    /// let evens = numbers.extract_if(.., |x| *x % 2 == 0).collect::<Vec<_>>();
     /// let odds = numbers;
     ///
     /// assert_eq!(evens, vec![2, 4, 6, 8, 14]);
     /// assert_eq!(odds, vec![1, 3, 5, 9, 11, 13, 15]);
     /// ```
+    ///
+    /// Using the range argument to only process a part of the vector:
+    ///
+    /// ```
+    /// #![feature(extract_if)]
+    /// let mut items = vec![0, 0, 0, 0, 0, 0, 0, 1, 2, 1, 2, 1, 2];
+    /// let ones = items.extract_if(7.., |x| *x == 1).collect::<Vec<_>>();
+    /// assert_eq!(items, vec![0, 0, 0, 0, 0, 0, 0, 2, 2, 2]);
+    /// assert_eq!(ones.len(), 3);
+    /// ```
     #[unstable(feature = "extract_if", reason = "recently added", issue = "43244")]
-    pub fn extract_if<F>(&mut self, filter: F) -> ExtractIf<'_, T, F, A>
+    pub fn extract_if<F, R>(&mut self, range: R, filter: F) -> ExtractIf<'_, T, F, A>
     where
         F: FnMut(&mut T) -> bool,
+        R: RangeBounds<usize>,
     {
-        let old_len = self.len();
-
-        // Guard against us getting leaked (leak amplification)
-        unsafe {
-            self.set_len(0);
-        }
-
-        ExtractIf { vec: self, idx: 0, del: 0, old_len, pred: filter }
+        ExtractIf::new(self, filter, range)
     }
 }