Auto merge of #78461 - TimDiekmann:vec-alloc, r=Amanieu

Add support for custom allocators in `Vec`

This follows the [roadmap](rust-lang/wg-allocators#7) of the allocator WG to add custom allocators to collections.

r? `@Amanieu`

This pull request requires a crater run.

### Prior work:
- #71873: Crater-test to solve rust-lang/wg-allocators#1
- [`alloc-wg`](https://github.com/TimDiekmann/alloc-wg)-crate

library/alloc/src/boxed.rs

@@ -1347,9 +1347,10 @@ impl<I> FromIterator<I> for Box<[I]> {
 }
 
 #[stable(feature = "box_slice_clone", since = "1.3.0")]
-impl<T: Clone> Clone for Box<[T]> {
+impl<T: Clone, A: AllocRef + Clone> Clone for Box<[T], A> {
     fn clone(&self) -> Self {
-        self.to_vec().into_boxed_slice()
+        let alloc = Box::alloc_ref(self).clone();
+        self.to_vec_in(alloc).into_boxed_slice()
     }
 
     fn clone_from(&mut self, other: &Self) {

library/alloc/src/raw_vec.rs

@@ -233,15 +233,10 @@ impl<T, A: AllocRef> RawVec<T, A> {
     }
 
     /// Returns a shared reference to the allocator backing this `RawVec`.
-    pub fn alloc(&self) -> &A {
+    pub fn alloc_ref(&self) -> &A {
         &self.alloc
     }
 
-    /// Returns a mutable reference to the allocator backing this `RawVec`.
-    pub fn alloc_mut(&mut self) -> &mut A {
-        &mut self.alloc
-    }
-
     fn current_memory(&self) -> Option<(NonNull<u8>, Layout)> {
         if mem::size_of::<T>() == 0 || self.cap == 0 {
             None

library/alloc/src/slice.rs

@@ -87,6 +87,7 @@ use core::cmp::Ordering::{self, Less};
 use core::mem::{self, size_of};
 use core::ptr;
 
+use crate::alloc::{AllocRef, Global};
 use crate::borrow::ToOwned;
 use crate::boxed::Box;
 use crate::vec::Vec;
@@ -137,26 +138,28 @@ pub use hack::to_vec;
 // `core::slice::SliceExt` - we need to supply these functions for the
 // `test_permutations` test
 mod hack {
+    use core::alloc::AllocRef;
+
     use crate::boxed::Box;
     use crate::vec::Vec;
 
     // We shouldn't add inline attribute to this since this is used in
     // `vec!` macro mostly and causes perf regression. See #71204 for
     // discussion and perf results.
-    pub fn into_vec<T>(b: Box<[T]>) -> Vec<T> {
+    pub fn into_vec<T, A: AllocRef>(b: Box<[T], A>) -> Vec<T, A> {
         unsafe {
             let len = b.len();
-            let b = Box::into_raw(b);
-            Vec::from_raw_parts(b as *mut T, len, len)
+            let (b, alloc) = Box::into_raw_with_alloc(b);
+            Vec::from_raw_parts_in(b as *mut T, len, len, alloc)
         }
     }
 
     #[inline]
-    pub fn to_vec<T>(s: &[T]) -> Vec<T>
+    pub fn to_vec<T, A: AllocRef>(s: &[T], alloc: A) -> Vec<T, A>
     where
         T: Clone,
     {
-        let mut vec = Vec::with_capacity(s.len());
+        let mut vec = Vec::with_capacity_in(s.len(), alloc);
         vec.extend_from_slice(s);
         vec
     }
@@ -388,11 +391,33 @@ impl<T> [T] {
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn to_vec(&self) -> Vec<T>
+    where
+        T: Clone,
+    {
+        self.to_vec_in(Global)
+    }
+
+    /// Copies `self` into a new `Vec` with an allocator.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(allocator_api)]
+    ///
+    /// use std::alloc::System;
+    ///
+    /// let s = [10, 40, 30];
+    /// let x = s.to_vec_in(System);
+    /// // Here, `s` and `x` can be modified independently.
+    /// ```
+    #[inline]
+    #[unstable(feature = "allocator_api", issue = "32838")]
+    pub fn to_vec_in<A: AllocRef>(&self, alloc: A) -> Vec<T, A>
     where
         T: Clone,
     {
         // N.B., see the `hack` module in this file for more details.
-        hack::to_vec(self)
+        hack::to_vec(self, alloc)
     }
 
     /// Converts `self` into a vector without clones or allocation.
@@ -411,7 +436,7 @@ impl<T> [T] {
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
-    pub fn into_vec(self: Box<Self>) -> Vec<T> {
+    pub fn into_vec<A: AllocRef>(self: Box<Self, A>) -> Vec<T, A> {
         // N.B., see the `hack` module in this file for more details.
         hack::into_vec(self)
     }
@@ -730,7 +755,7 @@ impl<T: Clone> ToOwned for [T] {
 
     #[cfg(test)]
     fn to_owned(&self) -> Vec<T> {
-        hack::to_vec(self)
+        hack::to_vec(self, Global)
     }
 
     fn clone_into(&self, target: &mut Vec<T>) {