Rollup merge of rust-lang#147708 - clarfonthey:const-drop, r=oli-obk

const `mem::drop`

I'm putting this under the `const Destruct` feature flag since it doesn't really feel relevant to put it elsewhere… it's just an empty function body, so, it doesn't have any particular weirdness attached to it (unlike `drop_in_place`, for example).

r? wg-const-eval

Author: matthiaskrgr

core/src/mem/mod.rs

@@ -6,7 +6,7 @@
 #![stable(feature = "rust1", since = "1.0.0")]
 
 use crate::alloc::Layout;
-use crate::marker::DiscriminantKind;
+use crate::marker::{Destruct, DiscriminantKind};
 use crate::panic::const_assert;
 use crate::{clone, cmp, fmt, hash, intrinsics, ptr};
 
@@ -958,8 +958,13 @@ pub const fn replace<T>(dest: &mut T, src: T) -> T {
 /// [`RefCell`]: crate::cell::RefCell
 #[inline]
 #[stable(feature = "rust1", since = "1.0.0")]
+#[rustc_const_unstable(feature = "const_destruct", issue = "133214")]
 #[rustc_diagnostic_item = "mem_drop"]
-pub fn drop<T>(_x: T) {}
+pub const fn drop<T>(_x: T)
+where
+    T: [const] Destruct,
+{
+}
 
 /// Bitwise-copies a value.
 ///