Rollup merge of rust-lang#119411 - yotamofek:array-ptr-get, r=Nilstrieb

Add as_(mut_)ptr and as_(mut_)slice to raw array pointers

Hey, first time contributing to the standard libraries so not completely sure about the process.

These functions are complementary to the ones being added in rust-lang#74265 . I found them missing on array pointers.

See also:
- ACP: rust-lang/libs-team#321
- Tracking issue: rust-lang#119834

library/core/src/lib.rs

@@ -112,6 +112,7 @@
 //
 // Library features:
 // tidy-alphabetical-start
+#![feature(array_ptr_get)]
 #![feature(char_indices_offset)]
 #![feature(const_align_of_val)]
 #![feature(const_align_of_val_raw)]

library/core/src/ptr/const_ptr.rs

@@ -1798,6 +1798,46 @@ impl<T> *const [T] {
     }
 }
 
+impl<T, const N: usize> *const [T; N] {
+    /// Returns a raw pointer to the array's buffer.
+    ///
+    /// This is equivalent to casting `self` to `*const T`, but more type-safe.
+    ///
+    /// # Examples
+    ///
+    /// ```rust
+    /// #![feature(array_ptr_get)]
+    /// use std::ptr;
+    ///
+    /// let arr: *const [i8; 3] = ptr::null();
+    /// assert_eq!(arr.as_ptr(), ptr::null());
+    /// ```
+    #[inline]
+    #[unstable(feature = "array_ptr_get", issue = "119834")]
+    #[rustc_const_unstable(feature = "array_ptr_get", issue = "119834")]
+    pub const fn as_ptr(self) -> *const T {
+        self as *const T
+    }
+
+    /// Returns a raw pointer to a slice containing the entire array.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(array_ptr_get, slice_ptr_len)]
+    ///
+    /// let arr: *const [i32; 3] = &[1, 2, 4] as *const [i32; 3];
+    /// let slice: *const [i32] = arr.as_slice();
+    /// assert_eq!(slice.len(), 3);
+    /// ```
+    #[inline]
+    #[unstable(feature = "array_ptr_get", issue = "119834")]
+    #[rustc_const_unstable(feature = "array_ptr_get", issue = "119834")]
+    pub const fn as_slice(self) -> *const [T] {
+        self
+    }
+}
+
 // Equality for pointers
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T: ?Sized> PartialEq for *const T {

library/core/src/ptr/mut_ptr.rs

@@ -2209,6 +2209,49 @@ impl<T> *mut [T] {
     }
 }
 
+impl<T, const N: usize> *mut [T; N] {
+    /// Returns a raw pointer to the array's buffer.
+    ///
+    /// This is equivalent to casting `self` to `*mut T`, but more type-safe.
+    ///
+    /// # Examples
+    ///
+    /// ```rust
+    /// #![feature(array_ptr_get)]
+    /// use std::ptr;
+    ///
+    /// let arr: *mut [i8; 3] = ptr::null_mut();
+    /// assert_eq!(arr.as_mut_ptr(), ptr::null_mut());
+    /// ```
+    #[inline]
+    #[unstable(feature = "array_ptr_get", issue = "119834")]
+    #[rustc_const_unstable(feature = "array_ptr_get", issue = "119834")]
+    pub const fn as_mut_ptr(self) -> *mut T {
+        self as *mut T
+    }
+
+    /// Returns a raw pointer to a mutable slice containing the entire array.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(array_ptr_get)]
+    ///
+    /// let mut arr = [1, 2, 5];
+    /// let ptr: *mut [i32; 3] = &mut arr;
+    /// unsafe {
+    ///     (&mut *ptr.as_mut_slice())[..2].copy_from_slice(&[3, 4]);
+    /// }
+    /// assert_eq!(arr, [3, 4, 5]);
+    /// ```
+    #[inline]
+    #[unstable(feature = "array_ptr_get", issue = "119834")]
+    #[rustc_const_unstable(feature = "array_ptr_get", issue = "119834")]
+    pub const fn as_mut_slice(self) -> *mut [T] {
+        self
+    }
+}
+
 // Equality for pointers
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T: ?Sized> PartialEq for *mut T {

library/core/tests/lib.rs

@@ -1,5 +1,6 @@
 #![feature(alloc_layout_extra)]
 #![feature(array_chunks)]
+#![feature(array_ptr_get)]
 #![feature(array_windows)]
 #![feature(ascii_char)]
 #![feature(ascii_char_variants)]
@@ -52,6 +53,7 @@
 #![feature(sort_internals)]
 #![feature(slice_take)]
 #![feature(slice_from_ptr_range)]
+#![feature(slice_ptr_len)]
 #![feature(slice_split_once)]
 #![feature(split_as_slice)]
 #![feature(maybe_uninit_fill)]

library/core/tests/ptr.rs

@@ -1141,3 +1141,16 @@ fn test_const_copy() {
         assert!(*ptr2 == 1);
     };
 }
+
+#[test]
+fn test_null_array_as_slice() {
+    let arr: *mut [u8; 4] = null_mut();
+    let ptr: *mut [u8] = arr.as_mut_slice();
+    assert!(ptr.is_null());
+    assert_eq!(ptr.len(), 4);
+
+    let arr: *const [u8; 4] = null();
+    let ptr: *const [u8] = arr.as_slice();
+    assert!(ptr.is_null());
+    assert_eq!(ptr.len(), 4);
+}