Make Option::as_[mut_]slice const

library/core/src/option.rs

@@ -797,7 +797,8 @@ impl<T> Option<T> {
  #[inline]
  #[must_use]
  #[stable(feature = "option_as_slice", since = "1.75.0")]
- pub fn as_slice(&self) -> &[T] {
+ #[rustc_const_unstable(feature = "const_option_ext", issue = "91930")]
+ pub const fn as_slice(&self) -> &[T] {
  // SAFETY: When the `Option` is `Some`, we're using the actual pointer
  // to the payload, with a length of 1, so this is equivalent to
  // `slice::from_ref`, and thus is safe.
@@ -811,7 +812,7 @@ impl<T> Option<T> {
  unsafe {
  slice::from_raw_parts(
  (self as *const Self).byte_add(core::mem::offset_of!(Self, Some.0)).cast(),
- usize::from(self.is_some()),
+ self.is_some() as usize,
  )
  }
  }
@@ -851,7 +852,8 @@ impl<T> Option<T> {
  #[inline]
  #[must_use]
  #[stable(feature = "option_as_slice", since = "1.75.0")]
- pub fn as_mut_slice(&mut self) -> &mut [T] {
+ #[rustc_const_unstable(feature = "const_option_ext", issue = "91930")]
+ pub const fn as_mut_slice(&mut self) -> &mut [T] {
  // SAFETY: When the `Option` is `Some`, we're using the actual pointer
  // to the payload, with a length of 1, so this is equivalent to
  // `slice::from_mut`, and thus is safe.
@@ -867,7 +869,7 @@ impl<T> Option<T> {
  unsafe {
  slice::from_raw_parts_mut(
  (self as *mut Self).byte_add(core::mem::offset_of!(Self, Some.0)).cast(),
- usize::from(self.is_some()),
+ self.is_some() as usize,
  )
  }
  }

library/core/tests/option.rs

@@ -574,4 +574,13 @@ fn as_slice() {
  assert_eq!(Some(43).as_mut_slice(), &[43]);
  assert_eq!(None::<i32>.as_slice(), &[]);
  assert_eq!(None::<i32>.as_mut_slice(), &[]);
+
+ const A: &[u32] = Some(44).as_slice();
+ const B: &[u32] = None.as_slice();
+ const _: () = {
+ let [45] = Some(45).as_mut_slice() else { panic!() };
+ let []: &[u32] = None.as_mut_slice() else { panic!() };
+ };
+ assert_eq!(A, &[44]);
+ assert_eq!(B, &[]);
 }