Move Arc::allocator to T: ?Sized

Author: zachs18

library/alloc/src/sync.rs

@@ -683,16 +683,6 @@ impl<T> Arc<T> {
 }
 
 impl<T, A: Allocator> Arc<T, A> {
-    /// Returns a reference to the underlying allocator.
-    ///
-    /// Note: this is an associated function, which means that you have
-    /// to call it as `Arc::allocator(&a)` instead of `a.allocator()`. This
-    /// is so that there is no conflict with a method on the inner type.
-    #[inline]
-    #[unstable(feature = "allocator_api", issue = "32838")]
-    pub fn allocator(this: &Self) -> &A {
-        &this.alloc
-    }
     /// Constructs a new `Arc<T>` in the provided allocator.
     ///
     /// # Examples
@@ -1443,6 +1433,17 @@ impl<T: ?Sized> Arc<T> {
 }
 
 impl<T: ?Sized, A: Allocator> Arc<T, A> {
+    /// Returns a reference to the underlying allocator.
+    ///
+    /// Note: this is an associated function, which means that you have
+    /// to call it as `Arc::allocator(&a)` instead of `a.allocator()`. This
+    /// is so that there is no conflict with a method on the inner type.
+    #[inline]
+    #[unstable(feature = "allocator_api", issue = "32838")]
+    pub fn allocator(this: &Self) -> &A {
+        &this.alloc
+    }
+
     /// Consumes the `Arc`, returning the wrapped pointer.
     ///
     /// To avoid a memory leak the pointer must be converted back to an `Arc` using