Rollup merge of rust-lang#81730 - RustyYato:object-safe-allocator, r=…

…Amanieu

Make `Allocator` object-safe

This allows rust-lang/wg-allocators#83: polymorphic allocators

library/core/src/alloc/mod.rs

@@ -342,7 +342,10 @@ pub unsafe trait Allocator {
  ///
  /// The returned adaptor also implements `Allocator` and will simply borrow this.
  #[inline(always)]
- fn by_ref(&self) -> &Self {
+ fn by_ref(&self) -> &Self
+ where
+ Self: Sized,
+ {
  self
  }
 }

src/test/ui/allocator/object-safe.rs

@@ -0,0 +1,13 @@
+// run-pass
+
+// Check that `Allocator` is object safe, this allows for polymorphic allocators
+
+#![feature(allocator_api)]
+
+use std::alloc::{Allocator, System};
+
+fn ensure_object_safe(_: &dyn Allocator) {}
+
+fn main() {
+ ensure_object_safe(&System);
+}