Document ManuallyDrop and AssertUnwindSafe impls

Author: Jules-Bertholet

library/core/src/mem/manually_drop.rs

@@ -277,6 +277,8 @@ impl<T: ?Sized> DerefMut for ManuallyDrop<T> {
 #[unstable(feature = "deref_pure_trait", issue = "87121")]
 unsafe impl<T: ?Sized> DerefPure for ManuallyDrop<T> {}
 
+/// If a value's type is `Copy`, then it has a trivial destructor,
+/// so wrapping it in `ManuallyDrop` can never have undesired effects.
 #[stable(feature = "from_wrapper_impls", since = "CURRENT_RUSTC_VERSION")]
 impl<T> From<T> for ManuallyDrop<T>
 where

library/core/src/panic/unwind_safe.rs

@@ -312,6 +312,8 @@ impl<S: AsyncIterator> AsyncIterator for AssertUnwindSafe<S> {
     }
 }
 
+/// If a value's type is already `UnwindSafe`,
+/// wrapping it in `AssertUnwindSafe` is never incorrect.
 #[stable(feature = "from_wrapper_impls", since = "CURRENT_RUSTC_VERSION")]
 impl<T> From<T> for AssertUnwindSafe<T>
 where