library: Stabilize const_replace

Depends on stabilizing `const_ptr_write`.

Const-stabilizes:
- `core::mem::replace`
- `core::ptr::replace`

core/src/lib.rs

@@ -138,7 +138,6 @@
 #![feature(const_ptr_is_null)]
 #![feature(const_ptr_sub_ptr)]
 #![feature(const_raw_ptr_comparison)]
-#![feature(const_replace)]
 #![feature(const_size_of_val)]
 #![feature(const_size_of_val_raw)]
 #![feature(const_strict_overflow_ops)]

core/src/mem/mod.rs

@@ -857,7 +857,8 @@ pub fn take<T: Default>(dest: &mut T) -> T {
 #[inline]
 #[stable(feature = "rust1", since = "1.0.0")]
 #[must_use = "if you don't need the old value, you can just assign the new value directly"]
-#[rustc_const_unstable(feature = "const_replace", issue = "83164")]
+#[cfg_attr(bootstrap, rustc_allow_const_fn_unstable(const_mut_refs))]
+#[rustc_const_stable(feature = "const_replace", since = "CURRENT_RUSTC_VERSION")]
 #[cfg_attr(not(test), rustc_diagnostic_item = "mem_replace")]
 pub const fn replace<T>(dest: &mut T, src: T) -> T {
     // It may be tempting to use `swap` to avoid `unsafe` here. Don't!

core/src/ptr/mod.rs

@@ -1263,7 +1263,8 @@ const unsafe fn swap_nonoverlapping_simple_untyped<T>(x: *mut T, y: *mut T, coun
 /// ```
 #[inline]
 #[stable(feature = "rust1", since = "1.0.0")]
-#[rustc_const_unstable(feature = "const_replace", issue = "83164")]
+#[cfg_attr(bootstrap, rustc_allow_const_fn_unstable(const_mut_refs))]
+#[rustc_const_stable(feature = "const_replace", since = "CURRENT_RUSTC_VERSION")]
 #[rustc_diagnostic_item = "ptr_replace"]
 pub const unsafe fn replace<T>(dst: *mut T, src: T) -> T {
     // SAFETY: the caller must guarantee that `dst` is valid to be