From 57d2323ae91d3bc3887acefd7ce74e34f8784743 Mon Sep 17 00:00:00 2001
From: Sebastian McKenzie <sebmck@gmail.com>
Date: Tue, 28 Jul 2015 01:19:59 +0100
Subject: [PATCH] deopt on binding identifiers with same rest name - fixes
 #2091

---
 .../transformers/es6/parameters/rest.js              | 12 ++++++++++++
 .../rest-binding-deoptimisation/actal.js             |  1 +
 .../rest-binding-deoptimisation/expected.js          |  9 +++++++++
 3 files changed, 22 insertions(+)
 create mode 100644 packages/babel/test/fixtures/transformation/es6.parameters/rest-binding-deoptimisation/actal.js
 create mode 100644 packages/babel/test/fixtures/transformation/es6.parameters/rest-binding-deoptimisation/expected.js

diff --git a/packages/babel/src/transformation/transformers/es6/parameters/rest.js b/packages/babel/src/transformation/transformers/es6/parameters/rest.js
index 963e070d17..5388a37a8e 100644
--- a/packages/babel/src/transformation/transformers/es6/parameters/rest.js
+++ b/packages/babel/src/transformation/transformers/es6/parameters/rest.js
@@ -78,6 +78,18 @@ var memberExpressionOptimisationVisitor = {
 
       state.references.push(this);
     }
+  },
+
+  /**
+   * Deopt on use of a binding identifier with the same name as our rest param.
+   *
+   * See https://github.com/babel/babel/issues/2091
+   */
+
+  BindingIdentifier(node, parent, scope, state) {
+    if (node.name === state.name) {
+      state.deopted = true;
+    }
   }
 };
 
diff --git a/packages/babel/test/fixtures/transformation/es6.parameters/rest-binding-deoptimisation/actal.js b/packages/babel/test/fixtures/transformation/es6.parameters/rest-binding-deoptimisation/actal.js
new file mode 100644
index 0000000000..43adbba736
--- /dev/null
+++ b/packages/babel/test/fixtures/transformation/es6.parameters/rest-binding-deoptimisation/actal.js
@@ -0,0 +1 @@
+const deepAssign = (...args) => args = [];
diff --git a/packages/babel/test/fixtures/transformation/es6.parameters/rest-binding-deoptimisation/expected.js b/packages/babel/test/fixtures/transformation/es6.parameters/rest-binding-deoptimisation/expected.js
new file mode 100644
index 0000000000..b5288257f7
--- /dev/null
+++ b/packages/babel/test/fixtures/transformation/es6.parameters/rest-binding-deoptimisation/expected.js
@@ -0,0 +1,9 @@
+"use strict";
+
+var deepAssign = function deepAssign() {
+  for (var _len = arguments.length, args = Array(_len), _key = 0; _key < _len; _key++) {
+    args[_key] = arguments[_key];
+  }
+
+  return args = [];
+};