Rollup merge of #90998 - jhpratt:require-const-stability, r=oli-obk

Require const stability attribute on all stable functions that are `const`

This PR requires all stable functions (of all kinds) that are `const fn` to have a `#[rustc_const_stable]` or `#[rustc_const_unstable]` attribute. Stability was previously implied if omitted; a follow-up PR is planned to change the fallback to be unstable.

Author: matthiaskrgr

core/src/array/mod.rs

@@ -512,6 +512,7 @@ impl<T, const N: usize> [T; N] {
 
     /// Returns a slice containing the entire array. Equivalent to `&s[..]`.
     #[stable(feature = "array_as_slice", since = "1.57.0")]
+    #[rustc_const_stable(feature = "array_as_slice", since = "1.57.0")]
     pub const fn as_slice(&self) -> &[T] {
         self
     }

core/src/cell.rs

@@ -1959,6 +1959,7 @@ impl<T: ?Sized> UnsafeCell<T> {
     /// ```
     #[inline(always)]
     #[stable(feature = "unsafe_cell_raw_get", since = "1.56.0")]
+    #[rustc_const_stable(feature = "unsafe_cell_raw_get", since = "1.56.0")]
     pub const fn raw_get(this: *const Self) -> *mut T {
         // We can just cast the pointer from `UnsafeCell<T>` to `T` because of
         // #[repr(transparent)]. This exploits libstd's special status, there is

core/src/num/int_macros.rs

@@ -1064,6 +1064,7 @@ macro_rules! int_impl {
         ///
         /// ```
         #[stable(feature = "saturating_div", since = "1.58.0")]
+        #[rustc_const_stable(feature = "saturating_div", since = "1.58.0")]
         #[must_use = "this returns the result of the operation, \
                       without modifying the original"]
         #[inline]

core/src/num/nonzero.rs

@@ -972,6 +972,7 @@ macro_rules! nonzero_unsigned_is_power_of_two {
                 /// ```
                 #[must_use]
                 #[stable(feature = "nonzero_is_power_of_two", since = "1.59.0")]
+                #[rustc_const_stable(feature = "nonzero_is_power_of_two", since = "1.59.0")]
                 #[inline]
                 pub const fn is_power_of_two(self) -> bool {
                     // LLVM 11 normalizes `unchecked_sub(x, 1) & x == 0` to the implementation seen here.

core/src/num/uint_macros.rs

@@ -1132,6 +1132,7 @@ macro_rules! uint_impl {
         ///
         /// ```
         #[stable(feature = "saturating_div", since = "1.58.0")]
+        #[rustc_const_stable(feature = "saturating_div", since = "1.58.0")]
         #[must_use = "this returns the result of the operation, \
                       without modifying the original"]
         #[inline]