Safety comment

ivarflakstad · oli-obk · izagawd · commit 03486284a173 · 2025-12-15T16:31:01.000-04:00
Co-authored-by: Oli Scherer &lt;github35764891676564198441@oli-obk.de&gt;
diff --git a/library/core/src/any.rs b/library/core/src/any.rs
@@ -920,6 +920,8 @@ pub const fn downcast_trait<
     match vtable {
         Some(dyn_metadata) => {
             let pointer = ptr::from_raw_parts(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 { &*pointer })
         }
         None => None,

Original file line number	Diff line number	Diff line change
`@@ -920,6 +920,8 @@ pub const fn downcast_trait<`
`920`	`920`	`match vtable {`
`921`	`921`	`Some(dyn_metadata) => {`
`922`	`922`	`let pointer = ptr::from_raw_parts(t, dyn_metadata);`
	`923`	+ // SAFETY: `t` is a reference to a type, so we know it is valid.
	`924`	+ // `dyn_metadata` is a vtable for T, implementing the trait of `U`.
`923`	`925`	`Some(unsafe { &*pointer })`
`924`	`926`	`}`
`925`	`927`	`None => None,`