Rollup merge of rust-lang#131120 - tgross35:stabilize-const_option, r…

…=RalfJung

Stabilize `const_option`

This makes the following API stable in const contexts:

```rust
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: <rust-lang#67441>

alloc/src/lib.rs

@@ -111,7 +111,6 @@
 #![feature(const_eval_select)]
 #![feature(const_heap)]
 #![feature(const_maybe_uninit_write)]
-#![feature(const_option)]
 #![feature(const_pin)]
 #![feature(const_size_of_val)]
 #![feature(const_vec_string_slice)]

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();

core/src/lib.rs

@@ -131,7 +131,6 @@
 #![feature(const_maybe_uninit_assume_init)]
 #![feature(const_nonnull_new)]
 #![feature(const_num_midpoint)]
-#![feature(const_option)]
 #![feature(const_option_ext)]
 #![feature(const_pin)]
 #![feature(const_pointer_is_aligned)]

core/src/option.rs

@@ -723,7 +723,8 @@ impl<T> Option<T> {
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
-    #[rustc_const_unstable(feature = "const_option", issue = "67441")]
+    #[cfg_attr(bootstrap, rustc_allow_const_fn_unstable(const_mut_refs))]
+    #[rustc_const_stable(feature = "const_option", since = "CURRENT_RUSTC_VERSION")]
     pub const fn as_mut(&mut self) -> Option<&mut T> {
         match *self {
             Some(ref mut x) => Some(x),
@@ -924,7 +925,8 @@ impl<T> Option<T> {
     #[track_caller]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[cfg_attr(not(test), rustc_diagnostic_item = "option_expect")]
-    #[rustc_const_unstable(feature = "const_option", issue = "67441")]
+    #[rustc_allow_const_fn_unstable(const_precise_live_drops)]
+    #[rustc_const_stable(feature = "const_option", since = "CURRENT_RUSTC_VERSION")]
     pub const fn expect(self, msg: &str) -> T {
         match self {
             Some(val) => val,
@@ -962,7 +964,8 @@ impl<T> Option<T> {
     #[track_caller]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[cfg_attr(not(test), rustc_diagnostic_item = "option_unwrap")]
-    #[rustc_const_unstable(feature = "const_option", issue = "67441")]
+    #[rustc_allow_const_fn_unstable(const_precise_live_drops)]
+    #[rustc_const_stable(feature = "const_option", since = "CURRENT_RUSTC_VERSION")]
     pub const fn unwrap(self) -> T {
         match self {
             Some(val) => val,
@@ -1069,7 +1072,8 @@ impl<T> Option<T> {
     #[inline]
     #[track_caller]
     #[stable(feature = "option_result_unwrap_unchecked", since = "1.58.0")]
-    #[rustc_const_unstable(feature = "const_option", issue = "67441")]
+    #[rustc_allow_const_fn_unstable(const_precise_live_drops)]
+    #[rustc_const_stable(feature = "const_option", since = "CURRENT_RUSTC_VERSION")]
     pub const unsafe fn unwrap_unchecked(self) -> T {
         match self {
             Some(val) => val,
@@ -1712,7 +1716,8 @@ impl<T> Option<T> {
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
-    #[rustc_const_unstable(feature = "const_option", issue = "67441")]
+    #[cfg_attr(bootstrap, rustc_allow_const_fn_unstable(const_mut_refs))]
+    #[rustc_const_stable(feature = "const_option", since = "CURRENT_RUSTC_VERSION")]
     pub const fn take(&mut self) -> Option<T> {
         // FIXME(const-hack) replace `mem::replace` by `mem::take` when the latter is const ready
         mem::replace(self, None)
@@ -1769,8 +1774,9 @@ impl<T> Option<T> {
     /// assert_eq!(old, None);
     /// ```
     #[inline]
-    #[rustc_const_unstable(feature = "const_option", issue = "67441")]
     #[stable(feature = "option_replace", since = "1.31.0")]
+    #[cfg_attr(bootstrap, rustc_allow_const_fn_unstable(const_mut_refs))]
+    #[rustc_const_stable(feature = "const_option", since = "CURRENT_RUSTC_VERSION")]
     pub const fn replace(&mut self, value: T) -> Option<T> {
         mem::replace(self, Some(value))
     }
@@ -1878,7 +1884,7 @@ impl<T> Option<&T> {
     /// ```
     #[must_use = "`self` will be dropped if the result is not used"]
     #[stable(feature = "copied", since = "1.35.0")]
-    #[rustc_const_unstable(feature = "const_option", issue = "67441")]
+    #[rustc_const_stable(feature = "const_option", since = "CURRENT_RUSTC_VERSION")]
     pub const fn copied(self) -> Option<T>
     where
         T: Copy,
@@ -1931,7 +1937,8 @@ impl<T> Option<&mut T> {
     /// ```
     #[must_use = "`self` will be dropped if the result is not used"]
     #[stable(feature = "copied", since = "1.35.0")]
-    #[rustc_const_unstable(feature = "const_option", issue = "67441")]
+    #[cfg_attr(bootstrap, rustc_allow_const_fn_unstable(const_mut_refs))]
+    #[rustc_const_stable(feature = "const_option", since = "CURRENT_RUSTC_VERSION")]
     pub const fn copied(self) -> Option<T>
     where
         T: Copy,
@@ -1986,7 +1993,8 @@ impl<T, E> Option<Result<T, E>> {
     /// ```
     #[inline]
     #[stable(feature = "transpose_result", since = "1.33.0")]
-    #[rustc_const_unstable(feature = "const_option", issue = "67441")]
+    #[rustc_allow_const_fn_unstable(const_precise_live_drops)]
+    #[rustc_const_stable(feature = "const_option", since = "CURRENT_RUSTC_VERSION")]
     pub const fn transpose(self) -> Result<Option<T>, E> {
         match self {
             Some(Ok(x)) => Ok(Some(x)),
@@ -2009,7 +2017,6 @@ const fn unwrap_failed() -> ! {
 #[cfg_attr(feature = "panic_immediate_abort", inline)]
 #[cold]
 #[track_caller]
-#[rustc_const_unstable(feature = "const_option", issue = "67441")]
 const fn expect_failed(msg: &str) -> ! {
     panic_display(&msg)
 }
@@ -2534,7 +2541,8 @@ impl<T> Option<Option<T>> {
     /// ```
     #[inline]
     #[stable(feature = "option_flattening", since = "1.40.0")]
-    #[rustc_const_unstable(feature = "const_option", issue = "67441")]
+    #[rustc_allow_const_fn_unstable(const_precise_live_drops)]
+    #[rustc_const_stable(feature = "const_option", since = "CURRENT_RUSTC_VERSION")]
     pub const fn flatten(self) -> Option<T> {
         // FIXME(const-hack): could be written with `and_then`
         match self {

core/src/ptr/non_null.rs

@@ -1211,7 +1211,6 @@ impl<T: ?Sized> NonNull<T> {
     ///
     /// ```
     /// #![feature(const_nonnull_new)]
-    /// #![feature(const_option)]
     /// #![feature(const_pointer_is_aligned)]
     /// use std::ptr::NonNull;
     ///
@@ -1264,7 +1263,6 @@ impl<T: ?Sized> NonNull<T> {
     ///
     /// ```
     /// #![feature(const_pointer_is_aligned)]
-    /// #![feature(const_option)]
     /// #![feature(const_nonnull_new)]
     /// use std::ptr::NonNull;
     ///

core/src/time.rs

@@ -626,7 +626,6 @@ impl Duration {
     /// ```
     #[stable(feature = "duration_abs_diff", since = "1.81.0")]
     #[rustc_const_stable(feature = "duration_abs_diff", since = "1.81.0")]
-    #[rustc_allow_const_fn_unstable(const_option)]
     #[must_use = "this returns the result of the operation, \
                   without modifying the original"]
     #[inline]

core/tests/lib.rs

@@ -24,7 +24,6 @@
 #![feature(const_ipv6)]
 #![feature(const_likely)]
 #![feature(const_nonnull_new)]
-#![feature(const_option)]
 #![feature(const_option_ext)]
 #![feature(const_pin)]
 #![feature(const_pointer_is_aligned)]