Auto merge of rust-lang#97419 - WaffleLapkin:const_from_ptr_range, r=oli-obk

Make `from{,_mut}_ptr_range` const

This PR makes the following APIs `const`:
```rust
// core::slice

pub const unsafe fn from_ptr_range<'a, T>(range: Range<*const T>) -> &'a [T];
pub const unsafe fn from_mut_ptr_range<'a, T>(range: Range<*mut T>) -> &'a mut [T];
```

Tracking issue: rust-lang#89792.
Feature for `from_ptr_range` as a `const fn`: `slice_from_ptr_range_const`.
Feature for `from_mut_ptr_range` as a `const fn`: `slice_from_mut_ptr_range_const`.

r? `@oli-obk`

Author: bors

alloc/src/lib.rs

@@ -130,6 +130,7 @@
 #![feature(ptr_sub_ptr)]
 #![feature(receiver_trait)]
 #![feature(set_ptr_value)]
+#![feature(slice_from_ptr_range)]
 #![feature(slice_group_by)]
 #![feature(slice_ptr_get)]
 #![feature(slice_ptr_len)]

alloc/src/slice.rs

@@ -114,6 +114,8 @@ pub use core::slice::EscapeAscii;
 pub use core::slice::SliceIndex;
 #[stable(feature = "from_ref", since = "1.28.0")]
 pub use core::slice::{from_mut, from_ref};
+#[unstable(feature = "slice_from_ptr_range", issue = "89792")]
+pub use core::slice::{from_mut_ptr_range, from_ptr_range};
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use core::slice::{from_raw_parts, from_raw_parts_mut};
 #[stable(feature = "rust1", since = "1.0.0")]

core/src/slice/raw.rs

@@ -213,7 +213,8 @@ pub const fn from_mut<T>(s: &mut T) -> &mut [T] {
 ///
 /// [valid]: ptr#safety
 #[unstable(feature = "slice_from_ptr_range", issue = "89792")]
-pub unsafe fn from_ptr_range<'a, T>(range: Range<*const T>) -> &'a [T] {
+#[rustc_const_unstable(feature = "const_slice_from_ptr_range", issue = "89792")]
+pub const unsafe fn from_ptr_range<'a, T>(range: Range<*const T>) -> &'a [T] {
     // SAFETY: the caller must uphold the safety contract for `from_ptr_range`.
     unsafe { from_raw_parts(range.start, range.end.sub_ptr(range.start)) }
 }
@@ -263,7 +264,8 @@ pub unsafe fn from_ptr_range<'a, T>(range: Range<*const T>) -> &'a [T] {
 ///
 /// [valid]: ptr#safety
 #[unstable(feature = "slice_from_ptr_range", issue = "89792")]
-pub unsafe fn from_mut_ptr_range<'a, T>(range: Range<*mut T>) -> &'a mut [T] {
+#[rustc_const_unstable(feature = "slice_from_mut_ptr_range_const", issue = "89792")]
+pub const unsafe fn from_mut_ptr_range<'a, T>(range: Range<*mut T>) -> &'a mut [T] {
     // SAFETY: the caller must uphold the safety contract for `from_mut_ptr_range`.
     unsafe { from_raw_parts_mut(range.start, range.end.sub_ptr(range.start)) }
 }