Auto merge of #130538 - ultrabear:ultrabear_const_from_ref, r=workingjubilee

Stabilize const `{slice,array}::from_mut`

This PR stabilizes the following APIs as const stable as of rust `1.83`:
```rs
// core::array
pub const fn from_mut<T>(s: &mut T) -> &mut [T; 1];

// core::slice
pub const fn from_mut<T>(s: &mut T) -> &mut [T];
```
This is made possible by `const_mut_refs` being stabilized (yay).

Tracking issue: #90206

Author: bors

library/core/src/array/mod.rs

@@ -146,7 +146,8 @@ pub const fn from_ref<T>(s: &T) -> &[T; 1] {
 
 /// Converts a mutable reference to `T` into a mutable reference to an array of length 1 (without copying).
 #[stable(feature = "array_from_ref", since = "1.53.0")]
-#[rustc_const_unstable(feature = "const_array_from_ref", issue = "90206")]
+#[rustc_const_stable(feature = "const_array_from_ref", since = "CURRENT_RUSTC_VERSION")]
+#[cfg_attr(bootstrap, rustc_allow_const_fn_unstable(const_mut_refs))]
 pub const fn from_mut<T>(s: &mut T) -> &mut [T; 1] {
     // SAFETY: Converting `&mut T` to `&mut [T; 1]` is sound.
     unsafe { &mut *(s as *mut T).cast::<[T; 1]>() }

library/core/src/lib.rs

@@ -114,7 +114,6 @@
 #![feature(const_align_offset)]
 #![feature(const_alloc_layout)]
 #![feature(const_arguments_as_str)]
-#![feature(const_array_from_ref)]
 #![feature(const_array_into_iter_constructors)]
 #![feature(const_bigint_helper_methods)]
 #![feature(const_black_box)]
@@ -145,7 +144,6 @@
 #![feature(const_replace)]
 #![feature(const_size_of_val)]
 #![feature(const_size_of_val_raw)]
-#![feature(const_slice_from_ref)]
 #![feature(const_strict_overflow_ops)]
 #![feature(const_swap)]
 #![feature(const_try)]

library/core/src/slice/raw.rs

@@ -204,7 +204,8 @@ pub const fn from_ref<T>(s: &T) -> &[T] {
 
 /// Converts a reference to T into a slice of length 1 (without copying).
 #[stable(feature = "from_ref", since = "1.28.0")]
-#[rustc_const_unstable(feature = "const_slice_from_ref", issue = "90206")]
+#[rustc_const_stable(feature = "const_slice_from_ref", since = "CURRENT_RUSTC_VERSION")]
+#[cfg_attr(bootstrap, rustc_allow_const_fn_unstable(const_mut_refs))]
 #[must_use]
 pub const fn from_mut<T>(s: &mut T) -> &mut [T] {
     array::from_mut(s)

library/core/tests/lib.rs

@@ -16,7 +16,6 @@
 #![feature(clone_to_uninit)]
 #![feature(const_align_of_val_raw)]
 #![feature(const_align_offset)]
-#![feature(const_array_from_ref)]
 #![feature(const_black_box)]
 #![feature(const_hash)]
 #![feature(const_heap)]
@@ -31,7 +30,6 @@
 #![feature(const_pointer_is_aligned)]
 #![feature(const_ptr_write)]
 #![feature(const_result)]
-#![feature(const_slice_from_ref)]
 #![feature(const_three_way_compare)]
 #![feature(const_trait_impl)]
 #![feature(core_intrinsics)]