1 files changed, 10 insertions, 0 deletions
diff --git a/src/libsyntax/feature_gate.rs b/src/libsyntax/feature_gate.rs
index b86b92fb29e..84122688c83 100644
--- a/src/libsyntax/feature_gate.rs
+++ b/src/libsyntax/feature_gate.rs
@@ -499,6 +499,9 @@ declare_features! (
 
     // #[cfg_attr(predicate, multiple, attributes, here)]
     (active, cfg_attr_multi, "1.31.0", Some(54881), None),
+
+    // Allows `const _: TYPE = VALUE`
+    (active, underscore_const_names, "1.31.0", Some(54912), None),
 );
 
 declare_features! (
@@ -1583,6 +1586,13 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
                 }
             }
 
+            ast::ItemKind::Const(_,_) => {
+                if i.ident.name == "_" {
+                    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);
             }