Merging upstream version 6.7.7.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

8 files changed, 238 insertions, 314 deletions

diff --git a/rust/alloc/alloc.rs b/rust/alloc/alloc.rs
index 0b6bf5b6da..8cb4a31cf6 100644
--- a/rust/alloc/alloc.rs
+++ b/rust/alloc/alloc.rs
@@ -6,9 +6,7 @@
 
 #[cfg(not(test))]
 use core::intrinsics;
-use core::intrinsics::{min_align_of_val, size_of_val};
 
-use core::ptr::Unique;
 #[cfg(not(test))]
 use core::ptr::{self, NonNull};
 
@@ -40,7 +38,6 @@ extern "Rust" {
     #[rustc_nounwind]
     fn __rust_alloc_zeroed(size: usize, align: usize) -> *mut u8;
 
-    #[cfg(not(bootstrap))]
     static __rust_no_alloc_shim_is_unstable: u8;
 }
 
@@ -98,7 +95,6 @@ pub unsafe fn alloc(layout: Layout) -> *mut u8 {
     unsafe {
         // Make sure we don't accidentally allow omitting the allocator shim in
         // stable code until it is actually stabilized.
-        #[cfg(not(bootstrap))]
         core::ptr::read_volatile(&__rust_no_alloc_shim_is_unstable);
 
         __rust_alloc(layout.size(), layout.align())
@@ -339,22 +335,6 @@ unsafe fn exchange_malloc(size: usize, align: usize) -> *mut u8 {
     }
 }
 
-#[cfg_attr(not(test), lang = "box_free")]
-#[inline]
-// This signature has to be the same as `Box`, otherwise an ICE will happen.
-// When an additional parameter to `Box` is added (like `A: Allocator`), this has to be added here as
-// well.
-// For example if `Box` is changed to  `struct Box<T: ?Sized, A: Allocator>(Unique<T>, A)`,
-// this function has to be changed to `fn box_free<T: ?Sized, A: Allocator>(Unique<T>, A)` as well.
-pub(crate) unsafe fn box_free<T: ?Sized, A: Allocator>(ptr: Unique<T>, alloc: A) {
-    unsafe {
-        let size = size_of_val(ptr.as_ref());
-        let align = min_align_of_val(ptr.as_ref());
-        let layout = Layout::from_size_align_unchecked(size, align);
-        alloc.deallocate(From::from(ptr.cast()), layout)
-    }
-}
-
 // # Allocation error handler
 
 #[cfg(not(no_global_oom_handling))]
@@ -414,7 +394,6 @@ pub mod __alloc_error_handler {
             static __rust_alloc_error_handler_should_panic: u8;
         }
 
-        #[allow(unused_unsafe)]
         if unsafe { __rust_alloc_error_handler_should_panic != 0 } {
             panic!("memory allocation of {size} bytes failed")
         } else {
diff --git a/rust/alloc/boxed.rs b/rust/alloc/boxed.rs
index c8173cea83..9620eba172 100644
--- a/rust/alloc/boxed.rs
+++ b/rust/alloc/boxed.rs
@@ -159,12 +159,12 @@ use core::hash::{Hash, Hasher};
 use core::iter::FusedIterator;
 use core::marker::Tuple;
 use core::marker::Unsize;
-use core::mem;
+use core::mem::{self, SizedTypeProperties};
 use core::ops::{
     CoerceUnsized, Deref, DerefMut, DispatchFromDyn, Generator, GeneratorState, Receiver,
 };
 use core::pin::Pin;
-use core::ptr::{self, Unique};
+use core::ptr::{self, NonNull, Unique};
 use core::task::{Context, Poll};
 
 #[cfg(not(no_global_oom_handling))]
@@ -483,8 +483,12 @@ impl<T, A: Allocator> Box<T, A> {
     where
         A: Allocator,
     {
-        let layout = Layout::new::<mem::MaybeUninit<T>>();
-        let ptr = alloc.allocate(layout)?.cast();
+        let ptr = if T::IS_ZST {
+            NonNull::dangling()
+        } else {
+            let layout = Layout::new::<mem::MaybeUninit<T>>();
+            alloc.allocate(layout)?.cast()
+        };
         unsafe { Ok(Box::from_raw_in(ptr.as_ptr(), alloc)) }
     }
 
@@ -553,8 +557,12 @@ impl<T, A: Allocator> Box<T, A> {
     where
         A: Allocator,
     {
-        let layout = Layout::new::<mem::MaybeUninit<T>>();
-        let ptr = alloc.allocate_zeroed(layout)?.cast();
+        let ptr = if T::IS_ZST {
+            NonNull::dangling()
+        } else {
+            let layout = Layout::new::<mem::MaybeUninit<T>>();
+            alloc.allocate_zeroed(layout)?.cast()
+        };
         unsafe { Ok(Box::from_raw_in(ptr.as_ptr(), alloc)) }
     }
 
@@ -679,14 +687,16 @@ impl<T> Box<[T]> {
     #[unstable(feature = "allocator_api", issue = "32838")]
     #[inline]
     pub fn try_new_uninit_slice(len: usize) -> Result<Box<[mem::MaybeUninit<T>]>, AllocError> {
-        unsafe {
+        let ptr = if T::IS_ZST || len == 0 {
+            NonNull::dangling()
+        } else {
             let layout = match Layout::array::<mem::MaybeUninit<T>>(len) {
                 Ok(l) => l,
                 Err(_) => return Err(AllocError),
             };
-            let ptr = Global.allocate(layout)?;
-            Ok(RawVec::from_raw_parts_in(ptr.as_mut_ptr() as *mut _, len, Global).into_box(len))
-        }
+            Global.allocate(layout)?.cast()
+        };
+        unsafe { Ok(RawVec::from_raw_parts_in(ptr.as_ptr(), len, Global).into_box(len)) }
     }
 
     /// Constructs a new boxed slice with uninitialized contents, with the memory
@@ -711,14 +721,16 @@ impl<T> Box<[T]> {
     #[unstable(feature = "allocator_api", issue = "32838")]
     #[inline]
     pub fn try_new_zeroed_slice(len: usize) -> Result<Box<[mem::MaybeUninit<T>]>, AllocError> {
-        unsafe {
+        let ptr = if T::IS_ZST || len == 0 {
+            NonNull::dangling()
+        } else {
             let layout = match Layout::array::<mem::MaybeUninit<T>>(len) {
                 Ok(l) => l,
                 Err(_) => return Err(AllocError),
             };
-            let ptr = Global.allocate_zeroed(layout)?;
-            Ok(RawVec::from_raw_parts_in(ptr.as_mut_ptr() as *mut _, len, Global).into_box(len))
-        }
+            Global.allocate_zeroed(layout)?.cast()
+        };
+        unsafe { Ok(RawVec::from_raw_parts_in(ptr.as_ptr(), len, Global).into_box(len)) }
     }
 }
 
@@ -1215,8 +1227,18 @@ impl<T: ?Sized, A: Allocator> Box<T, A> {
 
 #[stable(feature = "rust1", since = "1.0.0")]
 unsafe impl<#[may_dangle] T: ?Sized, A: Allocator> Drop for Box<T, A> {
+    #[inline]
     fn drop(&mut self) {
-        // FIXME: Do nothing, drop is currently performed by compiler.
+        // the T in the Box is dropped by the compiler before the destructor is run
+
+        let ptr = self.0;
+
+        unsafe {
+            let layout = Layout::for_value_raw(ptr.as_ptr());
+            if layout.size() != 0 {
+                self.1.deallocate(From::from(ptr.cast()), layout);
+            }
+        }
     }
 }
 
@@ -2165,7 +2187,7 @@ impl dyn Error + Send {
         let err: Box<dyn Error> = self;
         <dyn Error>::downcast(err).map_err(|s| unsafe {
             // Reapply the `Send` marker.
-            mem::transmute::<Box<dyn Error>, Box<dyn Error + Send>>(s)
+            Box::from_raw(Box::into_raw(s) as *mut (dyn Error + Send))
         })
     }
 }
@@ -2179,7 +2201,7 @@ impl dyn Error + Send + Sync {
         let err: Box<dyn Error> = self;
         <dyn Error>::downcast(err).map_err(|s| unsafe {
             // Reapply the `Send + Sync` marker.
-            mem::transmute::<Box<dyn Error>, Box<dyn Error + Send + Sync>>(s)
+            Box::from_raw(Box::into_raw(s) as *mut (dyn Error + Send + Sync))
         })
     }
 }
diff --git a/rust/alloc/lib.rs b/rust/alloc/lib.rs
index 85e91356ec..73b9ffd845 100644
--- a/rust/alloc/lib.rs
+++ b/rust/alloc/lib.rs
@@ -58,6 +58,11 @@
 //! [`Rc`]: rc
 //! [`RefCell`]: core::cell
 
+// To run alloc tests without x.py without ending up with two copies of alloc, Miri needs to be
+// able to "empty" this crate. See <https://github.com/rust-lang/miri-test-libstd/issues/4>.
+// rustc itself never sets the feature, so this line has no effect there.
+#![cfg(any(not(feature = "miri-test-libstd"), test, doctest))]
+//
 #![allow(unused_attributes)]
 #![stable(feature = "alloc", since = "1.36.0")]
 #![doc(
@@ -77,11 +82,6 @@
 ))]
 #![no_std]
 #![needs_allocator]
-// To run alloc tests without x.py without ending up with two copies of alloc, Miri needs to be
-// able to "empty" this crate. See <https://github.com/rust-lang/miri-test-libstd/issues/4>.
-// rustc itself never sets the feature, so this line has no affect there.
-#![cfg(any(not(feature = "miri-test-libstd"), test, doctest))]
-//
 // Lints:
 #![deny(unsafe_op_in_unsafe_fn)]
 #![deny(fuzzy_provenance_casts)]
@@ -90,6 +90,8 @@
 #![warn(missing_docs)]
 #![allow(explicit_outlives_requirements)]
 #![warn(multiple_supertrait_upcastable)]
+#![cfg_attr(not(bootstrap), allow(internal_features))]
+#![cfg_attr(not(bootstrap), allow(rustdoc::redundant_explicit_links))]
 //
 // Library features:
 // tidy-alphabetical-start
@@ -139,7 +141,6 @@
 #![feature(maybe_uninit_uninit_array_transpose)]
 #![feature(pattern)]
 #![feature(pointer_byte_offsets)]
-#![feature(provide_any)]
 #![feature(ptr_internals)]
 #![feature(ptr_metadata)]
 #![feature(ptr_sub_ptr)]
diff --git a/rust/alloc/raw_vec.rs b/rust/alloc/raw_vec.rs
index 65d5ce1582..a7425582a3 100644
--- a/rust/alloc/raw_vec.rs
+++ b/rust/alloc/raw_vec.rs
@@ -471,16 +471,26 @@ impl<T, A: Allocator> RawVec<T, A> {
         let (ptr, layout) = if let Some(mem) = self.current_memory() { mem } else { return Ok(()) };
         // See current_memory() why this assert is here
         let _: () = const { assert!(mem::size_of::<T>() % mem::align_of::<T>() == 0) };
-        let ptr = unsafe {
-            // `Layout::array` cannot overflow here because it would have
-            // overflowed earlier when capacity was larger.
-            let new_size = mem::size_of::<T>().unchecked_mul(cap);
-            let new_layout = Layout::from_size_align_unchecked(new_size, layout.align());
-            self.alloc
-                .shrink(ptr, layout, new_layout)
-                .map_err(|_| AllocError { layout: new_layout, non_exhaustive: () })?
-        };
-        self.set_ptr_and_cap(ptr, cap);
+
+        // If shrinking to 0, deallocate the buffer. We don't reach this point
+        // for the T::IS_ZST case since current_memory() will have returned
+        // None.
+        if cap == 0 {
+            unsafe { self.alloc.deallocate(ptr, layout) };
+            self.ptr = Unique::dangling();
+            self.cap = 0;
+        } else {
+            let ptr = unsafe {
+                // `Layout::array` cannot overflow here because it would have
+                // overflowed earlier when capacity was larger.
+                let new_size = mem::size_of::<T>().unchecked_mul(cap);
+                let new_layout = Layout::from_size_align_unchecked(new_size, layout.align());
+                self.alloc
+                    .shrink(ptr, layout, new_layout)
+                    .map_err(|_| AllocError { layout: new_layout, non_exhaustive: () })?
+            };
+            self.set_ptr_and_cap(ptr, cap);
+        }
         Ok(())
     }
 }
diff --git a/rust/alloc/vec/drain_filter.rs b/rust/alloc/vec/drain_filter.rs
deleted file mode 100644
index 09efff090e..0000000000
--- a/rust/alloc/vec/drain_filter.rs
+++ /dev/null
@@ -1,199 +0,0 @@
-// SPDX-License-Identifier: Apache-2.0 OR MIT
-
-use crate::alloc::{Allocator, Global};
-use core::mem::{ManuallyDrop, SizedTypeProperties};
-use core::ptr;
-use core::slice;
-
-use super::Vec;
-
-/// An iterator which uses a closure to determine if an element should be removed.
-///
-/// This struct is created by [`Vec::drain_filter`].
-/// See its documentation for more.
-///
-/// # Example
-///
-/// ```
-/// #![feature(drain_filter)]
-///
-/// let mut v = vec![0, 1, 2];
-/// let iter: std::vec::DrainFilter<'_, _, _> = v.drain_filter(|x| *x % 2 == 0);
-/// ```
-#[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
-#[derive(Debug)]
-pub struct DrainFilter<
-    'a,
-    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>,
-    /// The index of the item that will be inspected by the next call to `next`.
-    pub(super) idx: usize,
-    /// The number of items that have been drained (removed) thus far.
-    pub(super) del: usize,
-    /// The original length of `vec` prior to draining.
-    pub(super) old_len: usize,
-    /// The filter test predicate.
-    pub(super) pred: F,
-    /// A flag that indicates a panic has occurred in the filter test predicate.
-    /// This is used as a hint in the drop implementation to prevent consumption
-    /// of the remainder of the `DrainFilter`. Any unprocessed items will be
-    /// backshifted in the `vec`, but no further items will be dropped or
-    /// tested by the filter predicate.
-    pub(super) panic_flag: bool,
-}
-
-impl<T, F, A: Allocator> DrainFilter<'_, T, F, A>
-where
-    F: FnMut(&mut T) -> bool,
-{
-    /// Returns a reference to the underlying allocator.
-    #[unstable(feature = "allocator_api", issue = "32838")]
-    #[inline]
-    pub fn allocator(&self) -> &A {
-        self.vec.allocator()
-    }
-
-    /// Keep unyielded elements in the source `Vec`.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// #![feature(drain_filter)]
-    /// #![feature(drain_keep_rest)]
-    ///
-    /// let mut vec = vec!['a', 'b', 'c'];
-    /// let mut drain = vec.drain_filter(|_| true);
-    ///
-    /// assert_eq!(drain.next().unwrap(), 'a');
-    ///
-    /// // This call keeps 'b' and 'c' in the vec.
-    /// drain.keep_rest();
-    ///
-    /// // If we wouldn't call `keep_rest()`,
-    /// // `vec` would be empty.
-    /// assert_eq!(vec, ['b', 'c']);
-    /// ```
-    #[unstable(feature = "drain_keep_rest", issue = "101122")]
-    pub fn keep_rest(self) {
-        // At this moment layout looks like this:
-        //
-        //  _____________________/-- old_len
-        // /                     \
-        // [kept] [yielded] [tail]
-        //        \_______/ ^-- idx
-        //                \-- del
-        //
-        // Normally `Drop` impl would drop [tail] (via .for_each(drop), ie still calling `pred`)
-        //
-        // 1. Move [tail] after [kept]
-        // 2. Update length of the original vec to `old_len - del`
-        //    a. In case of ZST, this is the only thing we want to do
-        // 3. Do *not* drop self, as everything is put in a consistent state already, there is nothing to do
-        let mut this = ManuallyDrop::new(self);
-
-        unsafe {
-            // ZSTs have no identity, so we don't need to move them around.
-            if !T::IS_ZST && this.idx < this.old_len && this.del > 0 {
-                let ptr = this.vec.as_mut_ptr();
-                let src = ptr.add(this.idx);
-                let dst = src.sub(this.del);
-                let tail_len = this.old_len - this.idx;
-                src.copy_to(dst, tail_len);
-            }
-
-            let new_len = this.old_len - this.del;
-            this.vec.set_len(new_len);
-        }
-    }
-}
-
-#[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
-impl<T, F, A: Allocator> Iterator for DrainFilter<'_, T, F, A>
-where
-    F: FnMut(&mut T) -> bool,
-{
-    type Item = T;
-
-    fn next(&mut self) -> Option<T> {
-        unsafe {
-            while self.idx < self.old_len {
-                let i = self.idx;
-                let v = slice::from_raw_parts_mut(self.vec.as_mut_ptr(), self.old_len);
-                self.panic_flag = true;
-                let drained = (self.pred)(&mut v[i]);
-                self.panic_flag = false;
-                // Update the index *after* the predicate is called. If the index
-                // is updated prior and the predicate panics, the element at this
-                // index would be leaked.
-                self.idx += 1;
-                if drained {
-                    self.del += 1;
-                    return Some(ptr::read(&v[i]));
-                } else if self.del > 0 {
-                    let del = self.del;
-                    let src: *const T = &v[i];
-                    let dst: *mut T = &mut v[i - del];
-                    ptr::copy_nonoverlapping(src, dst, 1);
-                }
-            }
-            None
-        }
-    }
-
-    fn size_hint(&self) -> (usize, Option<usize>) {
-        (0, Some(self.old_len - self.idx))
-    }
-}
-
-#[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
-impl<T, F, A: Allocator> Drop for DrainFilter<'_, T, F, A>
-where
-    F: FnMut(&mut T) -> bool,
-{
-    fn drop(&mut self) {
-        struct BackshiftOnDrop<'a, 'b, T, F, A: Allocator>
-        where
-            F: FnMut(&mut T) -> bool,
-        {
-            drain: &'b mut DrainFilter<'a, T, F, A>,
-        }
-
-        impl<'a, 'b, T, F, A: Allocator> Drop for BackshiftOnDrop<'a, 'b, T, F, A>
-        where
-            F: FnMut(&mut T) -> bool,
-        {
-            fn drop(&mut self) {
-                unsafe {
-                    if self.drain.idx < self.drain.old_len && self.drain.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.drain.vec.as_mut_ptr();
-                        let src = ptr.add(self.drain.idx);
-                        let dst = src.sub(self.drain.del);
-                        let tail_len = self.drain.old_len - self.drain.idx;
-                        src.copy_to(dst, tail_len);
-                    }
-                    self.drain.vec.set_len(self.drain.old_len - self.drain.del);
-                }
-            }
-        }
-
-        let backshift = BackshiftOnDrop { drain: self };
-
-        // Attempt to consume any remaining elements if the filter predicate
-        // has not yet panicked. We'll backshift any remaining elements
-        // whether we've already panicked or if the consumption here panics.
-        if !backshift.drain.panic_flag {
-            backshift.drain.for_each(drop);
-        }
-    }
-}
diff --git a/rust/alloc/vec/extract_if.rs b/rust/alloc/vec/extract_if.rs
new file mode 100644
index 0000000000..f314a51d4d
--- /dev/null
+++ b/rust/alloc/vec/extract_if.rs
@@ -0,0 +1,115 @@
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
+use crate::alloc::{Allocator, Global};
+use core::ptr;
+use core::slice;
+
+use super::Vec;
+
+/// An iterator which uses a closure to determine if an element should be removed.
+///
+/// This struct is created by [`Vec::extract_if`].
+/// See its documentation for more.
+///
+/// # Example
+///
+/// ```
+/// #![feature(extract_if)]
+///
+/// let mut v = vec![0, 1, 2];
+/// let iter: std::vec::ExtractIf<'_, _, _> = v.extract_if(|x| *x % 2 == 0);
+/// ```
+#[unstable(feature = "extract_if", reason = "recently added", issue = "43244")]
+#[derive(Debug)]
+#[must_use = "iterators are lazy and do nothing unless consumed"]
+pub struct ExtractIf<
+    'a,
+    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>,
+    /// The index of the item that will be inspected by the next call to `next`.
+    pub(super) idx: usize,
+    /// The number of items that have been drained (removed) thus far.
+    pub(super) del: usize,
+    /// The original length of `vec` prior to draining.
+    pub(super) old_len: usize,
+    /// The filter test predicate.
+    pub(super) pred: F,
+}
+
+impl<T, F, A: Allocator> ExtractIf<'_, T, F, A>
+where
+    F: FnMut(&mut T) -> bool,
+{
+    /// Returns a reference to the underlying allocator.
+    #[unstable(feature = "allocator_api", issue = "32838")]
+    #[inline]
+    pub fn allocator(&self) -> &A {
+        self.vec.allocator()
+    }
+}
+
+#[unstable(feature = "extract_if", reason = "recently added", issue = "43244")]
+impl<T, F, A: Allocator> Iterator for ExtractIf<'_, T, F, A>
+where
+    F: FnMut(&mut T) -> bool,
+{
+    type Item = T;
+
+    fn next(&mut self) -> Option<T> {
+        unsafe {
+            while self.idx < self.old_len {
+                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]);
+                // Update the index *after* the predicate is called. If the index
+                // is updated prior and the predicate panics, the element at this
+                // index would be leaked.
+                self.idx += 1;
+                if drained {
+                    self.del += 1;
+                    return Some(ptr::read(&v[i]));
+                } else if self.del > 0 {
+                    let del = self.del;
+                    let src: *const T = &v[i];
+                    let dst: *mut T = &mut v[i - del];
+                    ptr::copy_nonoverlapping(src, dst, 1);
+                }
+            }
+            None
+        }
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        (0, Some(self.old_len - 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,
+{
+    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);
+                let tail_len = self.old_len - self.idx;
+                src.copy_to(dst, tail_len);
+            }
+            self.vec.set_len(self.old_len - self.del);
+        }
+    }
+}
diff --git a/rust/alloc/vec/mod.rs b/rust/alloc/vec/mod.rs
index 05c70de022..209a88cfe5 100644
--- a/rust/alloc/vec/mod.rs
+++ b/rust/alloc/vec/mod.rs
@@ -74,10 +74,10 @@ use crate::boxed::Box;
 use crate::collections::{TryReserveError, TryReserveErrorKind};
 use crate::raw_vec::RawVec;
 
-#[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
-pub use self::drain_filter::DrainFilter;
+#[unstable(feature = "extract_if", reason = "recently added", issue = "43244")]
+pub use self::extract_if::ExtractIf;
 
-mod drain_filter;
+mod extract_if;
 
 #[cfg(not(no_global_oom_handling))]
 #[stable(feature = "vec_splice", since = "1.21.0")]
@@ -216,7 +216,7 @@ mod spec_extend;
 ///
 /// # Indexing
 ///
-/// The `Vec` type allows to access values by index, because it implements the
+/// The `Vec` type allows access to values by index, because it implements the
 /// [`Index`] trait. An example will be more explicit:
 ///
 /// ```
@@ -618,22 +618,20 @@ impl<T> Vec<T> {
     /// Using memory that was allocated elsewhere:
     ///
     /// ```rust
-    /// #![feature(allocator_api)]
-    ///
-    /// use std::alloc::{AllocError, Allocator, Global, Layout};
+    /// use std::alloc::{alloc, Layout};
     ///
     /// fn main() {
     ///     let layout = Layout::array::<u32>(16).expect("overflow cannot happen");
     ///
     ///     let vec = unsafe {
-    ///         let mem = match Global.allocate(layout) {
-    ///             Ok(mem) => mem.cast::<u32>().as_ptr(),
-    ///             Err(AllocError) => return,
-    ///         };
+    ///         let mem = alloc(layout).cast::<u32>();
+    ///         if mem.is_null() {
+    ///             return;
+    ///         }
     ///
     ///         mem.write(1_000_000);
     ///
-    ///         Vec::from_raw_parts_in(mem, 1, 16, Global)
+    ///         Vec::from_raw_parts(mem, 1, 16)
     ///     };
     ///
     ///     assert_eq!(vec, &[1_000_000]);
@@ -876,19 +874,22 @@ impl<T, A: Allocator> Vec<T, A> {
     /// Using memory that was allocated elsewhere:
     ///
     /// ```rust
-    /// use std::alloc::{alloc, Layout};
+    /// #![feature(allocator_api)]
+    ///
+    /// use std::alloc::{AllocError, Allocator, Global, Layout};
     ///
     /// fn main() {
     ///     let layout = Layout::array::<u32>(16).expect("overflow cannot happen");
+    ///
     ///     let vec = unsafe {
-    ///         let mem = alloc(layout).cast::<u32>();
-    ///         if mem.is_null() {
-    ///             return;
-    ///         }
+    ///         let mem = match Global.allocate(layout) {
+    ///             Ok(mem) => mem.cast::<u32>().as_ptr(),
+    ///             Err(AllocError) => return,
+    ///         };
     ///
     ///         mem.write(1_000_000);
     ///
-    ///         Vec::from_raw_parts(mem, 1, 16)
+    ///         Vec::from_raw_parts_in(mem, 1, 16, Global)
     ///     };
     ///
     ///     assert_eq!(vec, &[1_000_000]);
@@ -2507,7 +2508,7 @@ impl<T: Clone, A: Allocator> Vec<T, A> {
         let len = self.len();
 
         if new_len > len {
-            self.extend_with(new_len - len, ExtendElement(value))
+            self.extend_with(new_len - len, value)
         } else {
             self.truncate(new_len);
         }
@@ -2545,7 +2546,7 @@ impl<T: Clone, A: Allocator> Vec<T, A> {
         let len = self.len();
 
         if new_len > len {
-            self.try_extend_with(new_len - len, ExtendElement(value))
+            self.try_extend_with(new_len - len, value)
         } else {
             self.truncate(new_len);
             Ok(())
@@ -2684,26 +2685,10 @@ impl<T, A: Allocator, const N: usize> Vec<[T; N], A> {
     }
 }
 
-// This code generalizes `extend_with_{element,default}`.
-trait ExtendWith<T> {
-    fn next(&mut self) -> T;
-    fn last(self) -> T;
-}
-
-struct ExtendElement<T>(T);
-impl<T: Clone> ExtendWith<T> for ExtendElement<T> {
-    fn next(&mut self) -> T {
-        self.0.clone()
-    }
-    fn last(self) -> T {
-        self.0
-    }
-}
-
-impl<T, A: Allocator> Vec<T, A> {
+impl<T: Clone, A: Allocator> Vec<T, A> {
     #[cfg(not(no_global_oom_handling))]
-    /// Extend the vector by `n` values, using the given generator.
-    fn extend_with<E: ExtendWith<T>>(&mut self, n: usize, mut value: E) {
+    /// Extend the vector by `n` clones of value.
+    fn extend_with(&mut self, n: usize, value: T) {
         self.reserve(n);
 
         unsafe {
@@ -2715,15 +2700,15 @@ impl<T, A: Allocator> Vec<T, A> {
 
             // Write all elements except the last one
             for _ in 1..n {
-                ptr::write(ptr, value.next());
+                ptr::write(ptr, value.clone());
                 ptr = ptr.add(1);
-                // Increment the length in every step in case next() panics
+                // Increment the length in every step in case clone() panics
                 local_len.increment_len(1);
             }
 
             if n > 0 {
                 // We can write the last element directly without cloning needlessly
-                ptr::write(ptr, value.last());
+                ptr::write(ptr, value);
                 local_len.increment_len(1);
             }
 
@@ -2731,8 +2716,8 @@ impl<T, A: Allocator> Vec<T, A> {
         }
     }
 
-    /// Try to extend the vector by `n` values, using the given generator.
-    fn try_extend_with<E: ExtendWith<T>>(&mut self, n: usize, mut value: E) -> Result<(), TryReserveError> {
+    /// Try to extend the vector by `n` clones of value.
+    fn try_extend_with(&mut self, n: usize, value: T) -> Result<(), TryReserveError> {
         self.try_reserve(n)?;
 
         unsafe {
@@ -2744,15 +2729,15 @@ impl<T, A: Allocator> Vec<T, A> {
 
             // Write all elements except the last one
             for _ in 1..n {
-                ptr::write(ptr, value.next());
+                ptr::write(ptr, value.clone());
                 ptr = ptr.add(1);
-                // Increment the length in every step in case next() panics
+                // Increment the length in every step in case clone() panics
                 local_len.increment_len(1);
             }
 
             if n > 0 {
                 // We can write the last element directly without cloning needlessly
-                ptr::write(ptr, value.last());
+                ptr::write(ptr, value);
                 local_len.increment_len(1);
             }
 
@@ -3210,6 +3195,12 @@ impl<T, A: Allocator> Vec<T, A> {
     /// If the closure returns false, the element will remain in the vector and will not be yielded
     /// by the iterator.
     ///
+    /// 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.
+    ///
+    /// [`retain`]: Vec::retain
+    ///
     /// Using this method is equivalent to the following code:
     ///
     /// ```
@@ -3228,10 +3219,10 @@ impl<T, A: Allocator> Vec<T, A> {
     /// # assert_eq!(vec, vec![1, 4, 5]);
     /// ```
     ///
-    /// But `drain_filter` is easier to use. `drain_filter` is also more efficient,
+    /// 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 `drain_filter` also lets you mutate every element in the filter closure,
+    /// Note that `extract_if` also lets you mutate every element in the filter closure,
     /// regardless of whether you choose to keep or remove it.
     ///
     /// # Examples
@@ -3239,17 +3230,17 @@ impl<T, A: Allocator> Vec<T, A> {
     /// Splitting an array into evens and odds, reusing the original allocation:
     ///
     /// ```
-    /// #![feature(drain_filter)]
+    /// #![feature(extract_if)]
     /// let mut numbers = vec![1, 2, 3, 4, 5, 6, 8, 9, 11, 13, 14, 15];
     ///
-    /// let evens = numbers.drain_filter(|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]);
     /// ```
-    #[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
-    pub fn drain_filter<F>(&mut self, filter: F) -> DrainFilter<'_, T, F, A>
+    #[unstable(feature = "extract_if", reason = "recently added", issue = "43244")]
+    pub fn extract_if<F>(&mut self, filter: F) -> ExtractIf<'_, T, F, A>
     where
         F: FnMut(&mut T) -> bool,
     {
@@ -3260,7 +3251,7 @@ impl<T, A: Allocator> Vec<T, A> {
             self.set_len(0);
         }
 
-        DrainFilter { vec: self, idx: 0, del: 0, old_len, pred: filter, panic_flag: false }
+        ExtractIf { vec: self, idx: 0, del: 0, old_len, pred: filter }
     }
 }
 
@@ -3272,7 +3263,7 @@ impl<T, A: Allocator> Vec<T, A> {
 /// [`copy_from_slice`]: slice::copy_from_slice
 #[cfg(not(no_global_oom_handling))]
 #[stable(feature = "extend_ref", since = "1.2.0")]
-impl<'a, T: Copy + 'a, A: Allocator + 'a> Extend<&'a T> for Vec<T, A> {
+impl<'a, T: Copy + 'a, A: Allocator> Extend<&'a T> for Vec<T, A> {
     fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iter: I) {
         self.spec_extend(iter.into_iter())
     }
@@ -3290,9 +3281,14 @@ impl<'a, T: Copy + 'a, A: Allocator + 'a> Extend<&'a T> for Vec<T, A> {
 
 /// Implements comparison of vectors, [lexicographically](Ord#lexicographical-comparison).
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<T: PartialOrd, A: Allocator> PartialOrd for Vec<T, A> {
+impl<T, A1, A2> PartialOrd<Vec<T, A2>> for Vec<T, A1>
+where
+    T: PartialOrd,
+    A1: Allocator,
+    A2: Allocator,
+{
     #[inline]
-    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+    fn partial_cmp(&self, other: &Vec<T, A2>) -> Option<Ordering> {
         PartialOrd::partial_cmp(&**self, &**other)
     }
 }
diff --git a/rust/alloc/vec/spec_extend.rs b/rust/alloc/vec/spec_extend.rs
index a6a735201e..ada9195374 100644
--- a/rust/alloc/vec/spec_extend.rs
+++ b/rust/alloc/vec/spec_extend.rs
@@ -77,7 +77,7 @@ impl<T, A: Allocator> TrySpecExtend<T, IntoIter<T>> for Vec<T, A> {
 }
 
 #[cfg(not(no_global_oom_handling))]
-impl<'a, T: 'a, I, A: Allocator + 'a> SpecExtend<&'a T, I> for Vec<T, A>
+impl<'a, T: 'a, I, A: Allocator> SpecExtend<&'a T, I> for Vec<T, A>
 where
     I: Iterator<Item = &'a T>,
     T: Clone,
@@ -87,7 +87,7 @@ where
     }
 }
 
-impl<'a, T: 'a, I, A: Allocator + 'a> TrySpecExtend<&'a T, I> for Vec<T, A>
+impl<'a, T: 'a, I, A: Allocator> TrySpecExtend<&'a T, I> for Vec<T, A>
 where
     I: Iterator<Item = &'a T>,
     T: Clone,
@@ -98,7 +98,7 @@ where
 }
 
 #[cfg(not(no_global_oom_handling))]
-impl<'a, T: 'a, A: Allocator + 'a> SpecExtend<&'a T, slice::Iter<'a, T>> for Vec<T, A>
+impl<'a, T: 'a, A: Allocator> SpecExtend<&'a T, slice::Iter<'a, T>> for Vec<T, A>
 where
     T: Copy,
 {
@@ -108,7 +108,7 @@ where
     }
 }
 
-impl<'a, T: 'a, A: Allocator + 'a> TrySpecExtend<&'a T, slice::Iter<'a, T>> for Vec<T, A>
+impl<'a, T: 'a, A: Allocator> TrySpecExtend<&'a T, slice::Iter<'a, T>> for Vec<T, A>
 where
     T: Copy,
 {