Auto merge of rust-lang#72437 - ecstatic-morse:stabilize-const-if-match, r=oli-obk

Stabilize `#![feature(const_if_match)]`

Quoting from the [stabilization report](rust-lang#49146 (comment)):

> `if` and `match` expressions as well as the short-circuiting logic operators `&&` and `||` will become legal in all [const contexts](https://doc.rust-lang.org/reference/const_eval.html#const-context). A const context is any of the following:
>
> - The initializer of a `const`, `static`, `static mut` or enum discriminant.
> - The body of a `const fn`.
> - The value of a const generic (nightly only).
> - The length of an array type (`[u8; 3]`) or an array repeat expression (`[0u8; 3]`).
>
> Furthermore, the short-circuiting logic operators will no longer be lowered to their bitwise equivalents (`&` and `|` respectively) in `const` and `static` initializers (see rust-lang#57175). As a result, `let` bindings can be used alongside short-circuiting logic in those initializers.

Resolves rust-lang#49146.

Ideally, we would resolve 🐳 rust-lang#66753 before this lands on stable, so it might be worth pushing this back a release. Also, this means we should get the process started for rust-lang#52000, otherwise people will have no recourse except recursion for iterative `const fn`.

r? @oli-obk

Author: bors

src/doc/unstable-book/src/language-features/const-if-match.md

@@ -87,7 +87,7 @@
 #![feature(const_generic_impls_guard)]
 #![feature(const_generics)]
 #![feature(const_in_array_repeat_expressions)]
-#![feature(const_if_match)]
+#![cfg_attr(bootstrap, feature(const_if_match))]
 #![feature(cow_is_borrowed)]
 #![feature(dispatch_from_dyn)]
 #![feature(core_intrinsics)]

src/liballoc/lib.rs

@@ -73,8 +73,8 @@
 #![feature(const_ascii_ctype_on_intrinsics)]
 #![feature(const_alloc_layout)]
 #![feature(const_discriminant)]
-#![feature(const_if_match)]
-#![feature(const_loop)]
+#![cfg_attr(bootstrap, feature(const_if_match))]
+#![cfg_attr(bootstrap, feature(const_loop))]
 #![feature(const_checked_int_methods)]
 #![feature(const_euclidean_int_methods)]
 #![feature(const_overflowing_int_methods)]

src/libcore/lib.rs

@@ -1578,7 +1578,7 @@ $EndFeature, "
             #[stable(feature = "no_panic_abs", since = "1.13.0")]
             #[rustc_const_stable(feature = "const_int_methods", since = "1.32.0")]
             #[allow(unused_attributes)]
-            #[allow_internal_unstable(const_if_match)]
+            #[cfg_attr(bootstrap, allow_internal_unstable(const_if_match))]
             #[inline]
             pub const fn wrapping_abs(self) -> Self {
                  if self.is_negative() {
@@ -1867,7 +1867,7 @@ assert_eq!(", stringify!($SelfT), "::MIN.overflowing_neg(), (", stringify!($Self
             #[stable(feature = "wrapping", since = "1.7.0")]
             #[rustc_const_stable(feature = "const_int_methods", since = "1.32.0")]
             #[allow(unused_attributes)]
-            #[allow_internal_unstable(const_if_match)]
+            #[cfg_attr(bootstrap, allow_internal_unstable(const_if_match))]
             pub const fn overflowing_neg(self) -> (Self, bool) {
                 if self == Self::MIN {
                     (Self::MIN, true)
@@ -2160,7 +2160,7 @@ $EndFeature, "
             #[stable(feature = "rust1", since = "1.0.0")]
             #[rustc_const_stable(feature = "const_int_methods", since = "1.32.0")]
             #[allow(unused_attributes)]
-            #[allow_internal_unstable(const_if_match)]
+            #[cfg_attr(bootstrap, allow_internal_unstable(const_if_match))]
             #[inline]
             #[rustc_inherit_overflow_checks]
             pub const fn abs(self) -> Self {

src/libcore/num/mod.rs

@@ -7,7 +7,7 @@
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/", test(attr(deny(warnings))))]
 #![feature(bool_to_option)]
 #![feature(box_syntax)]
-#![feature(const_if_match)]
+#![cfg_attr(bootstrap, feature(const_if_match))]
 #![feature(const_fn)] // For the `transmute` in `P::new`
 #![feature(const_panic)]
 #![feature(const_transmute)]

src/librustc_ast/lib.rs

@@ -261,6 +261,10 @@ declare_features! (
     (accepted, transparent_enums, "1.42.0", Some(60405), None),
     /// Allows using subslice patterns, `[a, .., b]` and `[a, xs @ .., b]`.
     (accepted, slice_patterns, "1.42.0", Some(62254), None),
+    /// Allows the use of `if` and `match` in constants.
+    (accepted, const_if_match, "1.45.0", Some(49146), None),
+    /// Allows the use of `loop` and `while` in constants.
+    (accepted, const_loop, "1.45.0", Some(52000), None),
 
     // -------------------------------------------------------------------------
     // feature-group-end: accepted features

src/librustc_feature/accepted.rs

@@ -518,9 +518,6 @@ declare_features! (
     /// Allows using the `#[register_tool]` attribute.
     (active, register_tool, "1.41.0", Some(66079), None),
 
-    /// Allows the use of `if` and `match` in constants.
-    (active, const_if_match, "1.41.0", Some(49146), None),
-
     /// Allows the use of `#[cfg(sanitize = "option")]`; set when -Zsanitizer is used.
     (active, cfg_sanitize, "1.41.0", Some(39699), None),
 
@@ -530,9 +527,6 @@ declare_features! (
     /// Allows using `&mut` in constant functions.
     (active, const_mut_refs, "1.41.0", Some(57349), None),
 
-    /// Allows the use of `loop` and `while` in constants.
-    (active, const_loop, "1.41.0", Some(52000), None),
-
     /// Allows bindings in the subpattern of a binding pattern.
     /// For example, you can write `x @ Some(y)`.
     (active, bindings_after_at, "1.41.0", Some(65490), None),

src/librustc_feature/active.rs

@@ -3,7 +3,7 @@
 //! [rustc dev guide]: https://rustc-dev-guide.rust-lang.org/hir.html
 
 #![feature(crate_visibility_modifier)]
-#![feature(const_if_match)]
+#![cfg_attr(bootstrap, feature(const_if_match))]
 #![feature(const_fn)] // For the unsizing cast on `&[]`
 #![feature(const_panic)]
 #![feature(in_band_lifetimes)]

src/librustc_hir/lib.rs

@@ -1,5 +1,5 @@
 #![feature(allow_internal_unstable)]
-#![feature(const_if_match)]
+#![cfg_attr(bootstrap, feature(const_if_match))]
 #![feature(const_fn)]
 #![feature(const_panic)]
 #![feature(extend_one)]

src/librustc_index/lib.rs

@@ -17,7 +17,7 @@
 #![feature(box_patterns)]
 #![feature(box_syntax)]
 #![feature(const_fn)]
-#![feature(const_if_match)]
+#![cfg_attr(bootstrap, feature(const_if_match))]
 #![feature(const_panic)]
 #![feature(extend_one)]
 #![feature(never_type)]