parse const closures

compiler/rustc_ast/src/ast.rs

@@ -1307,6 +1307,7 @@ impl Expr {
 pub struct Closure {
     pub binder: ClosureBinder,
     pub capture_clause: CaptureBy,
+    pub constness: Const,
     pub asyncness: Async,
     pub movability: Movability,
     pub fn_decl: P<FnDecl>,

compiler/rustc_ast/src/mut_visit.rs

@@ -1362,6 +1362,7 @@ pub fn noop_visit_expr<T: MutVisitor>(
         ExprKind::Closure(box Closure {
             binder,
             capture_clause: _,
+            constness,
             asyncness,
             movability: _,
             fn_decl,
@@ -1370,6 +1371,7 @@ pub fn noop_visit_expr<T: MutVisitor>(
             fn_arg_span: _,
         }) => {
             vis.visit_closure_binder(binder);
+            visit_constness(constness, vis);
             vis.visit_asyncness(asyncness);
             vis.visit_fn_decl(fn_decl);
             vis.visit_expr(body);

compiler/rustc_ast/src/visit.rs

@@ -836,6 +836,7 @@ pub fn walk_expr<'a, V: Visitor<'a>>(visitor: &mut V, expression: &'a Expr) {
             binder,
             capture_clause: _,
             asyncness: _,
+            constness: _,
             movability: _,
             fn_decl,
             body,