Make forget intrinsic safe

[rust.git] / library / core / src / mem / mod.rs

diff --git a/library/core/src/mem/mod.rs b/library/core/src/mem/mod.rs
index a2c7da6e6958e2c9dacd0d9453ebee368157cf85..87956787242ac6216aa6396aa3af413c1498fc9d 100644 (file)
--- a/library/core/src/mem/mod.rs
+++ b/library/core/src/mem/mod.rs
@@ -151,9 +151,14 @@ pub const fn forget<T>(t: T) {
 #[inline]
 #[unstable(feature = "forget_unsized", issue = "none")]
 pub fn forget_unsized<T: ?Sized>(t: T) {
+    #[cfg(bootstrap)]
     // SAFETY: the forget intrinsic could be safe, but there's no point in making it safe since
     // we'll be implementing this function soon via `ManuallyDrop`
-    unsafe { intrinsics::forget(t) }
+    unsafe {
+        intrinsics::forget(t)
+    }
+    #[cfg(not(bootstrap))]
+    intrinsics::forget(t)
 }
 
 /// Returns the size of a type in bytes.
@@ -884,10 +889,10 @@ pub fn drop<T>(_x: T) {}
 /// Interprets `src` as having type `&U`, and then reads `src` without moving
 /// the contained value.
 ///
-/// This function will unsafely assume the pointer `src` is valid for
-/// [`size_of::<U>`][size_of] bytes by transmuting `&T` to `&U` and then reading
-/// the `&U`. It will also unsafely create a copy of the contained value instead of
-/// moving out of `src`.
+/// This function will unsafely assume the pointer `src` is valid for [`size_of::<U>`][size_of]
+/// bytes by transmuting `&T` to `&U` and then reading the `&U` (except that this is done in a way
+/// that is correct even when `&U` makes stricter alignment requirements than `&T`). It will also
+/// unsafely create a copy of the contained value instead of moving out of `src`.
 ///
 /// It is not a compile-time error if `T` and `U` have different sizes, but it
 /// is highly encouraged to only invoke this function where `T` and `U` have the