more intelligent scope tracking and insertion

lib/6to5/traverse/scope.js

@@ -45,7 +45,7 @@ Scope.prototype._add = function (node, references, throwOnDuplicate) {
     var id = ids[key];
 
     if (throwOnDuplicate && references[key]) {
-      throw this.file.errorWithNode(id, "Duplicate declaration");
+      throw this.file.errorWithNode(id, "Duplicate declaration", TypeError);
     }
 
     references[key] = id;
@@ -169,12 +169,11 @@ var functionVariableVisitor = {
 
 var blockVariableVisitor = {
   enter: function (node, parent, scope, context, add) {
-    if (t.isScope(node)) {
-      return context.skip();
-    }
-
     if (t.isBlockScoped(node)) {
       add(node, false, true);
+      context.stop();
+    } else if (t.isScope(node)) {
+      context.skip();
     }
   }
 };
@@ -277,13 +276,18 @@ Scope.prototype.push = function (opts) {
 };
 
 /**
- * Description
+ * Walk up the scope tree until we hit a `Function` and then
+ * push our `node` to it's references.
  *
  * @param {Object} node
  */
 
 Scope.prototype.add = function (node) {
-  this._add(node, this.references);
+  var scope = this;
+  while (scope.parent && !t.isFunction(scope.block)) {
+    scope = scope.parent;
+  }
+  scope._add(node, scope.references);
 };
 
 /**