Add feature gate for const generics

Author: varkor

src/libsyntax/ast.rs

@@ -323,12 +323,8 @@ impl fmt::Display for ParamKindOrd {
 pub enum GenericParamKind {
     /// A lifetime definition, e.g. `'a: 'b+'c+'d`.
     Lifetime,
-    Type {
-        default: Option<P<Ty>>,
-    },
-    Const {
-        ty: P<Ty>,
-    },
+    Type { default: Option<P<Ty>> },
+    Const { ty: P<Ty> },
 }
 
 #[derive(Clone, RustcEncodable, RustcDecodable, Debug)]

src/libsyntax/feature_gate.rs

@@ -27,7 +27,7 @@ use self::AttributeGate::*;
 
 use rustc_data_structures::fx::FxHashMap;
 use rustc_target::spec::abi::Abi;
-use ast::{self, NodeId, PatKind, RangeEnd};
+use ast::{self, NodeId, PatKind, RangeEnd, GenericParam, GenericParamKind};
 use attr;
 use source_map::Spanned;
 use edition::{ALL_EDITIONS, Edition};
@@ -429,6 +429,9 @@ declare_features! (
     // `existential type`
     (active, existential_type, "1.28.0", Some(34511), None),
 
+    // const generic types
+    (active, const_generics, "1.29.0", Some(44580), None),
+
     // unstable #[target_feature] directives
     (active, arm_target_feature, "1.27.0", Some(44839), None),
     (active, aarch64_target_feature, "1.27.0", Some(44839), None),
@@ -1818,6 +1821,14 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
         visit::walk_fn(self, fn_kind, fn_decl, span);
     }
 
+    fn visit_generic_param(&mut self, param: &'a GenericParam) {
+        if let GenericParamKind::Const { .. } = param.kind {
+            gate_feature_post!(&self, const_generics, param.ident.span,
+                "const generics are unstable");
+        }
+        visit::walk_generic_param(self, param);
+    }
+
     fn visit_trait_item(&mut self, ti: &'a ast::TraitItem) {
         match ti.node {
             ast::TraitItemKind::Method(ref sig, ref block) => {