Stabilize underscore_const_names.

src/librustc_data_structures/macros.rs

@@ -1,6 +1,7 @@
 /// A simple static assertion macro.
 #[macro_export]
-#[allow_internal_unstable(type_ascription, underscore_const_names)]
+#[cfg_attr(stage0, allow_internal_unstable(type_ascription, underscore_const_names))]
+#[cfg_attr(not(stage0), allow_internal_unstable(type_ascription))]
 macro_rules! static_assert {
     ($test:expr) => {
         // Use the bool to access an array such that if the bool is false, the access
@@ -12,7 +13,7 @@ macro_rules! static_assert {
 
 /// Type size assertion. The first argument is a type and the second argument is its expected size.
 #[macro_export]
-#[allow_internal_unstable(underscore_const_names)]
+#[cfg_attr(stage0, allow_internal_unstable(underscore_const_names))]
 macro_rules! static_assert_size {
     ($ty:ty, $size:expr) => {
         const _: [(); $size] = [(); ::std::mem::size_of::<$ty>()];

src/libsyntax/feature_gate.rs

@@ -25,7 +25,7 @@ use crate::source_map::Spanned;
 use crate::edition::{ALL_EDITIONS, Edition};
 use crate::visit::{self, FnKind, Visitor};
 use crate::parse::{token, ParseSess};
-use crate::symbol::{Symbol, kw, sym};
+use crate::symbol::{Symbol, sym};
 use crate::tokenstream::TokenTree;
 
 use errors::{Applicability, DiagnosticBuilder, Handler};
@@ -526,9 +526,6 @@ declare_features! (
     // Allows `impl Trait` in bindings (`let`, `const`, `static`).
     (active, impl_trait_in_bindings, "1.30.0", Some(34511), None),
 
-    // Allows `const _: TYPE = VALUE`.
-    (active, underscore_const_names, "1.31.0", Some(54912), None),
-
     // Allows using `reason` in lint attributes and the `#[expect(lint)]` lint check.
     (active, lint_reasons, "1.31.0", Some(54503), None),
 
@@ -843,6 +840,8 @@ declare_features! (
     // Allows using `#[repr(align(X))]` on enums with equivalent semantics
     // to wrapping an enum in a wrapper struct with `#[repr(align(X))]`.
     (accepted, repr_align_enum, "1.37.0", Some(57996), None),
+    // Allows `const _: TYPE = VALUE`.
+    (accepted, underscore_const_names, "1.37.0", Some(54912), None),
 
     // -------------------------------------------------------------------------
     // feature-group-end: accepted features
@@ -1992,13 +1991,6 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
 
     fn visit_item(&mut self, i: &'a ast::Item) {
         match i.node {
-            ast::ItemKind::Const(_,_) => {
-                if i.ident.name == kw::Underscore {
-                    gate_feature_post!(&self, underscore_const_names, i.span,
-                                        "naming constants with `_` is unstable");
-                }
-            }
-
             ast::ItemKind::ForeignMod(ref foreign_module) => {
                 self.check_abi(foreign_module.abi, i.span);
             }

src/test/ui/consts/const_short_circuit.rs

@@ -1,5 +1,3 @@
-#![feature(underscore_const_names)]
-
 const _: bool = false && false;
 const _: bool = true && false;
 const _: bool = {

src/test/ui/consts/const_short_circuit.stderr

@@ -1,23 +1,23 @@
 error: new features like let bindings are not permitted in constants which also use short circuiting operators
-  --> $DIR/const_short_circuit.rs:6:9
+  --> $DIR/const_short_circuit.rs:4:9
    |
 LL |     let mut x = true && false;
    |         ^^^^^
    |
 note: use of `&&` operator here does not actually short circuit due to the const evaluator presently not being able to do control flow. See https://github.com/rust-lang/rust/issues/49146 for more information.
-  --> $DIR/const_short_circuit.rs:6:22
+  --> $DIR/const_short_circuit.rs:4:22
    |
 LL |     let mut x = true && false;
    |                      ^^
 
 error: new features like let bindings are not permitted in constants which also use short circuiting operators
-  --> $DIR/const_short_circuit.rs:11:9
+  --> $DIR/const_short_circuit.rs:9:9
    |
 LL |     let x = true && false;
    |         ^
    |
 note: use of `&&` operator here does not actually short circuit due to the const evaluator presently not being able to do control flow. See https://github.com/rust-lang/rust/issues/49146 for more information.
-  --> $DIR/const_short_circuit.rs:11:18
+  --> $DIR/const_short_circuit.rs:9:18
    |
 LL |     let x = true && false;
    |                  ^^

src/test/ui/consts/underscore_const_names.rs

@@ -1,9 +1,9 @@
 // compile-pass
 
-#![feature(underscore_const_names)]
+#![deny(unused)]
 
 trait Trt {}
-struct Str {}
+pub struct Str {}
 impl Trt for Str {}
 
 macro_rules! check_impl {
@@ -17,7 +17,6 @@ macro_rules! check_impl {
     }
 }
 
-#[deny(unused)]
 const _ : () = ();
 
 const _ : i32 = 42;

src/test/ui/feature-gates/feature-gate-underscore_const_names.rs

@@ -1,14 +0,0 @@
-trait Trt {}
-struct Str {}
-
-impl Trt for Str {}
-
-const _ : () = {
-//~^ ERROR is unstable
-    use std::marker::PhantomData;
-    struct ImplementsTrait<T: Trt>(PhantomData<T>);
-    let _ = ImplementsTrait::<Str>(PhantomData);
-    ()
-};
-
-fn main() {}

src/test/ui/feature-gates/feature-gate-underscore_const_names.stderr

@@ -1,18 +0,0 @@
-error[E0658]: naming constants with `_` is unstable
-  --> $DIR/feature-gate-underscore_const_names.rs:6:1
-   |
-LL | / const _ : () = {
-LL | |
-LL | |     use std::marker::PhantomData;
-LL | |     struct ImplementsTrait<T: Trt>(PhantomData<T>);
-LL | |     let _ = ImplementsTrait::<Str>(PhantomData);
-LL | |     ()
-LL | | };
-   | |__^
-   |
-   = note: for more information, see https://github.com/rust-lang/rust/issues/54912
-   = help: add #![feature(underscore_const_names)] to the crate attributes to enable
-
-error: aborting due to previous error
-
-For more information about this error, try `rustc --explain E0658`.

src/test/ui/feature-gates/underscore_const_names_feature_gate.rs

@@ -1,3 +0,0 @@
-const _: () = (); //~ ERROR is unstable
-
-fn main() {}

src/test/ui/feature-gates/underscore_const_names_feature_gate.stderr

@@ -1,12 +0,0 @@
-error[E0658]: naming constants with `_` is unstable
-  --> $DIR/underscore_const_names_feature_gate.rs:1:1
-   |
-LL | const _: () = ();
-   | ^^^^^^^^^^^^^^^^^
-   |
-   = note: for more information, see https://github.com/rust-lang/rust/issues/54912
-   = help: add #![feature(underscore_const_names)] to the crate attributes to enable
-
-error: aborting due to previous error
-
-For more information about this error, try `rustc --explain E0658`.