Stabilize `const_option`

This makes the following API stable in const contexts:

    impl<T> Option<T> {
        pub const fn as_mut(&mut self) -> Option<&mut T>;
        pub const fn expect(self, msg: &str) -> T;
        pub const fn unwrap(self) -> T;
        pub const unsafe fn unwrap_unchecked(self) -> T;
        pub const fn take(&mut self) -> Option<T>;
        pub const fn replace(&mut self, value: T) -> Option<T>;
    }

    impl<T> Option<&T> {
        pub const fn copied(self) -> Option<T>
        where T: Copy;
    }

    impl<T> Option<&mut T> {
        pub const fn copied(self) -> Option<T>
        where T: Copy;
    }

    impl<T, E> Option<Result<T, E>> {
        pub const fn transpose(self) -> Result<Option<T>, E>
    }

    impl<T> Option<Option<T>> {
        pub const fn flatten(self) -> Option<T>;
    }

The following functions make use of the unstable
`const_precise_live_drops` feature:

- `expect`
- `unwrap`
- `unwrap_unchecked`
- `transpose`
- `flatten`

Fixes: <https://github.com/rust-lang/rust/issues/67441>

1 files changed, 0 insertions, 1 deletions

diff --git a/library/core/src/array/ascii.rs b/library/core/src/array/ascii.rs
index 05797b042ee..e2faef855bc 100644
--- a/library/core/src/array/ascii.rs
+++ b/library/core/src/array/ascii.rs
@@ -9,7 +9,6 @@ impl<const N: usize> [u8; N] {
     ///
     /// ```
     /// #![feature(ascii_char)]
-    /// #![feature(const_option)]
     ///
     /// const HEX_DIGITS: [std::ascii::Char; 16] =
     ///     *b"0123456789abcdef".as_ascii().unwrap();