Add SAFETY comment to downcast_trait_mut

ivarflakstad · izagawd · commit c55d87441092 · 2025-12-15T16:31:56.000-04:00
diff --git a/library/core/src/any.rs b/library/core/src/any.rs
@@ -941,6 +941,8 @@ pub const fn downcast_trait_mut<
     match vtable {
         Some(dyn_metadata) => {
             let pointer = ptr::from_raw_parts_mut(t, dyn_metadata);
+            // SAFETY: `t` is a reference to a type, so we know it is valid.
+            // `dyn_metadata` is a vtable for T, implementing the trait of `U`.
             Some(unsafe { &mut *pointer })
         }
         None => None,

Original file line number	Diff line number	Diff line change
`@@ -941,6 +941,8 @@ pub const fn downcast_trait_mut<`
`941`	`941`	`match vtable {`
`942`	`942`	`Some(dyn_metadata) => {`
`943`	`943`	`let pointer = ptr::from_raw_parts_mut(t, dyn_metadata);`
	`944`	+ // SAFETY: `t` is a reference to a type, so we know it is valid.
	`945`	+ // `dyn_metadata` is a vtable for T, implementing the trait of `U`.
`944`	`946`	`Some(unsafe { &mut *pointer })`
`945`	`947`	`}`
`946`	`948`	`None => None,`