nicer local exports remapping in default module formatter

lib/6to5/transformation/modules/_default.js

@@ -3,41 +3,52 @@ module.exports = DefaultFormatter;
 var traverse = require("../../traverse");
 var util     = require("../../util");
 var t        = require("../../types");
+var _        = require("lodash");
 
 function DefaultFormatter(file) {
   this.exports = [];
   this.file    = file;
 
-  var localExports = [];
-  traverse(file.ast, function (node) {
-    var declar = node && node.declaration;
-    if (t.isExportDeclaration(node) && declar && t.isStatement(declar)) {
-      localExports = localExports.concat(t.getIds(declar));
-    }
-  });
-  this.localExports = localExports;
-
+  this.localExports = this.getLocalExports();
   this.remapAssignments();
 }
 
+DefaultFormatter.prototype.getLocalExports = function () {
+  var localExports = {};
+
+  traverse(this.file.ast, {
+    enter: function (node) {
+      var declar = node && node.declaration;
+      if (t.isExportDeclaration(node) && declar && t.isStatement(declar)) {
+        _.extend(localExports, t.getIds(declar, true));
+      }
+    }
+  });
+
+  return localExports;
+};
+
 DefaultFormatter.prototype.remapAssignments = function () {
   var localExports = this.localExports;
 
-  traverse(this.file.ast, function (node) {
-    if (t.isExportDeclaration(node)) return false;
+  traverse(this.file.ast, {
+    enter: function (node, parent, scope) {
+      if (t.isExportDeclaration(node)) return false;
 
-    if (t.isAssignmentExpression(node)) {
-      var left = node.left;
-      if (t.isIdentifier(left) && localExports.indexOf(left.name) >= 0) {
-        return t.assignmentExpression(
-          "=",
-          left,
-          t.assignmentExpression(
-            node.operator,
-            t.memberExpression(t.identifier("exports"), left),
-            node.right
-          )
-        );
+      if (t.isAssignmentExpression(node)) {
+        var left = node.left;
+        var name = left.name;
+        if (t.isIdentifier(left) && localExports[name] && localExports[name] === scope.get(name, true)) {
+          return t.assignmentExpression(
+            "=",
+            left,
+            t.assignmentExpression(
+              node.operator,
+              t.memberExpression(t.identifier("exports"), left),
+              node.right
+            )
+          );
+        }
       }
     }
   });