gate const closures

compiler/rustc_ast_passes/src/feature_gate.rs

@@ -385,6 +385,14 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
             ast::ExprKind::TryBlock(_) => {
                 gate_feature_post!(&self, try_blocks, e.span, "`try` expression is experimental");
             }
+            ast::ExprKind::Closure(box ast::Closure { constness: ast::Const::Yes(_), .. }) => {
+                gate_feature_post!(
+                    &self,
+                    const_closures,
+                    e.span,
+                    "const closures are experimental"
+                );
+            }
             _ => {}
         }
         visit::walk_expr(self, e)

compiler/rustc_feature/src/active.rs

@@ -342,7 +342,9 @@ declare_features! (
     (active, collapse_debuginfo, "1.65.0", Some(100758), None),
     /// Allows `async {}` expressions in const contexts.
     (active, const_async_blocks, "1.53.0", Some(85368), None),
-    // Allows limiting the evaluation steps of const expressions
+    /// Allows `const || {}` closures in const contexts.
+    (incomplete, const_closures, "CURRENT_RUSTC_VERSION", Some(106003), None),
+    /// Allows limiting the evaluation steps of const expressions
     (active, const_eval_limit, "1.43.0", Some(67217), None),
     /// Allows the definition of `const extern fn` and `const unsafe extern fn`.
     (active, const_extern_fn, "1.40.0", Some(64926), None),

compiler/rustc_span/src/symbol.rs

@@ -498,6 +498,7 @@ symbols! {
         console,
         const_allocate,
         const_async_blocks,
+        const_closures,
         const_compare_raw_pointers,
         const_constructor,
         const_deallocate,

src/test/ui/rfc-2632-const-trait-impl/const_closures/gate.rs

@@ -0,0 +1,4 @@
+fn main() {
+    (const || {})();
+    //~^ ERROR: const closures are experimental
+}

src/test/ui/rfc-2632-const-trait-impl/const_closures/gate.stderr

@@ -0,0 +1,12 @@
+error[E0658]: const closures are experimental
+  --> $DIR/gate.rs:2:6
+   |
+LL |     (const || {})();
+   |      ^^^^^^^^^^^
+   |
+   = note: see issue #106003 <https://github.com/rust-lang/rust/issues/106003> for more information
+   = help: add `#![feature(const_closures)]` to the crate attributes to enable
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0658`.