Make Option::expect const

Author: lilasta

library/core/src/option.rs

@@ -703,7 +703,8 @@ impl<T> Option<T> {
     #[inline]
     #[track_caller]
     #[stable(feature = "rust1", since = "1.0.0")]
-    pub fn expect(self, msg: &str) -> T {
+    #[rustc_const_unstable(feature = "const_option", issue = "67441")]
+    pub const fn expect(self, msg: &str) -> T {
         match self {
             Some(val) => val,
             None => expect_failed(msg),
@@ -1634,7 +1635,7 @@ impl<T, E> Option<Result<T, E>> {
 #[inline(never)]
 #[cold]
 #[track_caller]
-fn expect_failed(msg: &str) -> ! {
+const fn expect_failed(msg: &str) -> ! {
     panic!("{}", msg)
 }