Merging upstream version 6.7.7.

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

4 files changed, 172 insertions, 260 deletions

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,
 {