test const Ref[Mut]

Author: Daniel-Aaron-Bloom

library/core/src/cell.rs

@@ -1502,7 +1502,8 @@ pub struct Ref<'b, T: ?Sized + 'b> {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<T: ?Sized> Deref for Ref<'_, T> {
+#[rustc_const_unstable(feature = "const_deref", issue = "88955")]
+impl<T: ?Sized> const Deref for Ref<'_, T> {
     type Target = T;
 
     #[inline]

library/coretests/tests/cell.rs

@@ -494,22 +494,27 @@ fn const_refcell() {
         {
             assert!(a.try_borrow().is_ok());
             assert!(a.try_borrow_mut().is_ok());
-            let _a = a.borrow();
+            let a_ref = a.borrow();
+            assert!(*a_ref == 0);
             assert!(a.try_borrow().is_ok());
             assert!(a.try_borrow_mut().is_err());
         }
         a
     };
     // Check that `borrow_mut` is usable at compile-time
     const BORROW_MUT_TEST: RefCell<u32> = {
-        let a = RefCell::new(0);
+        let mut a = RefCell::new(0);
         {
             assert!(a.try_borrow().is_ok());
             assert!(a.try_borrow_mut().is_ok());
-            let _a = a.borrow_mut();
+            let mut a_ref = a.borrow_mut();
+            assert!(*a_ref == 0);
+            *a_ref = 10;
+            assert!(*a_ref == 10);
             assert!(a.try_borrow().is_err());
             assert!(a.try_borrow_mut().is_err());
         }
+        assert!(*a.get_mut() == 10);
         a
     };
 

library/coretests/tests/lib.rs

@@ -15,6 +15,7 @@
 #![feature(cell_update)]
 #![feature(char_max_len)]
 #![feature(clone_to_uninit)]
+#![feature(const_deref)]
 #![feature(const_destruct)]
 #![feature(const_eval_select)]
 #![feature(const_ref_cell)]