Add feature gate

3 files changed, 4 insertions, 0 deletions

diff --git a/compiler/rustc_ast_passes/src/feature_gate.rs b/compiler/rustc_ast_passes/src/feature_gate.rs
index b960671bf6e..3d5056d82c5 100644
--- a/compiler/rustc_ast_passes/src/feature_gate.rs
+++ b/compiler/rustc_ast_passes/src/feature_gate.rs
@@ -603,6 +603,7 @@ pub fn check_crate(krate: &ast::Crate, sess: &Session) {
     gate_all!(yeet_expr, "`do yeet` expression is experimental");
     gate_all!(dyn_star, "`dyn*` trait objects are experimental");
     gate_all!(const_closures, "const closures are experimental");
+    gate_all!(builtin_syntax, "`builtin #` syntax is unstable");
 
     if !visitor.features.negative_bounds {
         for &span in spans.get(&sym::negative_bounds).iter().copied().flatten() {
diff --git a/compiler/rustc_feature/src/active.rs b/compiler/rustc_feature/src/active.rs
index 7e7df0e9584..a797dd94404 100644
--- a/compiler/rustc_feature/src/active.rs
+++ b/compiler/rustc_feature/src/active.rs
@@ -313,6 +313,8 @@ declare_features! (
     (active, async_closure, "1.37.0", Some(62290), None),
     /// Allows async functions to be declared, implemented, and used in traits.
     (active, async_fn_in_trait, "1.66.0", Some(91611), None),
+    /// Allows builtin # foo() syntax
+    (active, builtin_syntax, "CURRENT_RUSTC_VERSION", Some(110680), None),
     /// Allows `c"foo"` literals.
     (active, c_str_literals, "CURRENT_RUSTC_VERSION", Some(105723), None),
     /// Treat `extern "C"` function as nounwind.
diff --git a/compiler/rustc_parse/src/parser/expr.rs b/compiler/rustc_parse/src/parser/expr.rs
index b84a088a7b7..c1095512bd4 100644
--- a/compiler/rustc_parse/src/parser/expr.rs
+++ b/compiler/rustc_parse/src/parser/expr.rs
@@ -1782,6 +1782,7 @@ impl<'a> Parser<'a> {
                 .into_diagnostic(&self.sess.span_diagnostic);
             return Err(err);
         };
+        self.sess.gated_spans.gate(sym::builtin_syntax, ident.span);
         self.bump();
 
         self.expect(&TokenKind::OpenDelim(Delimiter::Parenthesis))?;