don't shadow default parameter scope iife and instead just apply the this and arguments - fixes #1128

src/babel/transformation/helpers/call-delegate.js

@@ -1,10 +1,33 @@
+import traverse from "../../traversal";
 import * as t from "../../types";
 
-export default function (node) {
-  var container = t.functionExpression(null, [], node.body, node.generator, node.async);
-  container.shadow = true;
+var visitor = {
+  enter(node, parent, scope, state) {
+    if (this.isThisExpression() || this.isReferencedIdentifier({ name: "arguments" })) {
+      state.found = true;
+      this.stop();
+    }
 
-  var call = t.callExpression(container, []);
+    if (this.isFunction()) {
+      this.skip();
+    }
+  }
+};
+
+export default function (node, scope) {
+  var container = t.functionExpression(null, [], node.body, node.generator, node.async);
+
+  var callee = container;
+  var args   = [];
+
+  var state = { found: false };
+  scope.traverse(node, visitor, state);
+  if (state.found) {
+    callee = t.memberExpression(container, t.identifier("apply"));
+    args = [t.thisExpression(), t.identifier("arguments")];
+  }
+
+  var call = t.callExpression(callee, args);
   if (node.generator) call = t.yieldExpression(call, true);
 
   return t.returnStatement(call);

src/babel/transformation/transformers/es6/parameters.default.js

@@ -92,7 +92,7 @@ exports.Function = function (node, parent, scope, file) {
   node.params = node.params.slice(0, lastNonDefaultParam);
 
   if (state.iife) {
-    body.push(callDelegate(node));
+    body.push(callDelegate(node, scope));
     node.body = t.blockStatement(body);
   } else {
     node.body.body = body.concat(node.body.body);