validate against multiple parents on `AST_Node` (#4032)

- fix related issues in `global_defs`, `ie8` & `reduce_vars`

1 files changed, 7 insertions, 0 deletions

diff --git a/lib/ast.js b/lib/ast.js
index 31072a08..093e192c 100644
--- a/lib/ast.js
+++ b/lib/ast.js
@@ -120,6 +120,13 @@ var AST_Node = DEFNODE("Node", "start end", {
             ctor.prototype._validate.call(this);
         } while (ctor = ctor.BASE);
     },
+    validate_ast: function() {
+        var marker = {};
+        this.walk(new TreeWalker(function(node) {
+            if (node.validate_visited === marker) throw new Error("invalid node reuse: " + node);
+            node.validate_visited = marker;
+        }));
+    },
 }, null);
 
 (AST_Node.log_function = function(fn, verbose) {