Rollup merge of #88551 - inquisitivecrystal:unsafe_cell_raw_get, r=m-ou-se

Stabilize `UnsafeCell::raw_get()`

This PR stabilizes the associated function `UnsafeCell::raw_get()`. The FCP has [already completed](https://github.com/rust-lang/rust/issues/66358#issuecomment-899095068). While there was some discussion about the naming after the close of the FCP, it looks like people have agreed on this name. Still, it would probably be best if a `libs-api` member had a look at this and stated whether more discussion is needed.

While I was at it, I added some tests for `UnsafeCell`, because there were barely any.

Closes #66358.

library/core/src/cell.rs

@@ -1921,7 +1921,7 @@ impl<T: ?Sized> UnsafeCell<T> {
     }
 
     /// Gets a mutable pointer to the wrapped value.
-    /// The difference to [`get`] is that this function accepts a raw pointer,
+    /// The difference from [`get`] is that this function accepts a raw pointer,
     /// which is useful to avoid the creation of temporary references.
     ///
     /// The result can be cast to a pointer of any kind.
@@ -1937,7 +1937,6 @@ impl<T: ?Sized> UnsafeCell<T> {
     /// calling `get` would require creating a reference to uninitialized data:
     ///
     /// ```
-    /// #![feature(unsafe_cell_raw_get)]
     /// use std::cell::UnsafeCell;
     /// use std::mem::MaybeUninit;
     ///
@@ -1948,7 +1947,7 @@ impl<T: ?Sized> UnsafeCell<T> {
     /// assert_eq!(uc.into_inner(), 5);
     /// ```
     #[inline(always)]
-    #[unstable(feature = "unsafe_cell_raw_get", issue = "66358")]
+    #[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

library/core/tests/cell.rs

@@ -2,6 +2,38 @@ use core::cell::*;
 use core::default::Default;
 use std::mem::drop;
 
+#[test]
+fn smoketest_unsafe_cell() {
+    let mut x = UnsafeCell::new(10);
+    let ref_mut = &mut x;
+    unsafe {
+        // The asserts are repeated in order to ensure that `get()`
+        // is non-mutating.
+        assert_eq!(*ref_mut.get(), 10);
+        assert_eq!(*ref_mut.get(), 10);
+        *ref_mut.get_mut() += 5;
+        assert_eq!(*ref_mut.get(), 15);
+        assert_eq!(*ref_mut.get(), 15);
+        assert_eq!(x.into_inner(), 15);
+    }
+}
+
+#[test]
+fn unsafe_cell_raw_get() {
+    let x = UnsafeCell::new(10);
+    let ptr = &x as *const UnsafeCell<i32>;
+    unsafe {
+        // The asserts are repeated in order to ensure that `raw_get()`
+        // is non-mutating.
+        assert_eq!(*UnsafeCell::raw_get(ptr), 10);
+        assert_eq!(*UnsafeCell::raw_get(ptr), 10);
+        *UnsafeCell::raw_get(ptr) += 5;
+        assert_eq!(*UnsafeCell::raw_get(ptr), 15);
+        assert_eq!(*UnsafeCell::raw_get(ptr), 15);
+        assert_eq!(x.into_inner(), 15);
+    }
+}
+
 #[test]
 fn smoketest_cell() {
     let x = Cell::new(10);

library/std/src/lib.rs

@@ -331,7 +331,6 @@
 #![feature(try_reserve)]
 #![feature(try_reserve_kind)]
 #![feature(unboxed_closures)]
-#![feature(unsafe_cell_raw_get)]
 #![feature(unwrap_infallible)]
 #![feature(vec_into_raw_parts)]
 #![feature(vec_spare_capacity)]