Add fn sync::Weak::allocator, remove A: Clone bound on Arc::unwrap_or_clone and From<Vec<T, A>> for Arc<[T], A>

Author: zachs18

library/alloc/src/sync.rs

@@ -2245,7 +2245,9 @@ impl<T: Clone, A: Allocator + Clone> Arc<T, A> {
         // either unique to begin with, or became one upon cloning the contents.
         unsafe { Self::get_mut_unchecked(this) }
     }
+}
 
+impl<T: Clone, A: Allocator> Arc<T, A> {
     /// If we have the only reference to `T` then unwrap it. Otherwise, clone `T` and return the
     /// clone.
     ///
@@ -2591,6 +2593,13 @@ impl<T> Weak<T> {
 }
 
 impl<T, A: Allocator> Weak<T, A> {
+    /// Returns a reference to the underlying allocator.
+    #[inline]
+    #[unstable(feature = "allocator_api", issue = "32838")]
+    pub fn allocator(&self) -> &A {
+        &self.alloc
+    }
+
     /// Constructs a new `Weak<T, A>`, without allocating any memory, technically in the provided
     /// allocator.
     /// Calling [`upgrade`] on the return value always gives [`None`].
@@ -3479,7 +3488,7 @@ impl<T: ?Sized, A: Allocator> From<Box<T, A>> for Arc<T, A> {
 
 #[cfg(not(no_global_oom_handling))]
 #[stable(feature = "shared_from_slice", since = "1.21.0")]
-impl<T, A: Allocator + Clone> From<Vec<T, A>> for Arc<[T], A> {
+impl<T, A: Allocator> From<Vec<T, A>> for Arc<[T], A> {
     /// Allocate a reference-counted slice and move `v`'s items into it.
     ///
     /// # Example