Make ExprKind::Closure a struct variant.

compiler/rustc_hir/src/intravisit.rs

@@ -1168,14 +1168,13 @@ pub fn walk_expr<'v, V: Visitor<'v>>(visitor: &mut V, expression: &'v Expr<'v>)
             visitor.visit_expr(subexpression);
             walk_list!(visitor, visit_arm, arms);
         }
-        ExprKind::Closure(_, ref function_declaration, body, _fn_decl_span, _gen) => visitor
-            .visit_fn(
-                FnKind::Closure,
-                function_declaration,
-                body,
-                expression.span,
-                expression.hir_id,
-            ),
+        ExprKind::Closure {
+            ref fn_decl,
+            body,
+            capture_clause: _,
+            fn_decl_span: _,
+            movability: _,
+        } => visitor.visit_fn(FnKind::Closure, fn_decl, body, expression.span, expression.hir_id),
         ExprKind::Block(ref block, ref opt_label) => {
             walk_list!(visitor, visit_label, opt_label);
             visitor.visit_block(block);