From 1696f77980da64e4bae5c1969a61837cd5a2eb43 Mon Sep 17 00:00:00 2001
From: Sebastian McKenzie <sebmck@gmail.com>
Date: Tue, 6 Jan 2015 20:15:10 +1100
Subject: [PATCH] fix rest parameter keys when on functions with params

---
 CHANGELOG.md                                        |  5 +++++
 lib/6to5/transformation/templates/rest.js           |  2 +-
 .../transformers/es6-rest-parameters.js             | 13 +++++++++++--
 .../es6-rest-parameters/multiple/expected.js        |  4 ++--
 4 files changed, 19 insertions(+), 5 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 1afbaabd28..8a29c9ec37 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -11,6 +11,11 @@
 
 _Note: Gaps between patch versions are faulty/broken releases._
 
+## 2.6.1
+
+ * **Bug Fix**
+  * Fix rest parameter keys when on functions with params.
+
 ## 2.6.1
 
  * **Bug Fix**
diff --git a/lib/6to5/transformation/templates/rest.js b/lib/6to5/transformation/templates/rest.js
index ca3dfabbef..f396f01117 100644
--- a/lib/6to5/transformation/templates/rest.js
+++ b/lib/6to5/transformation/templates/rest.js
@@ -1,3 +1,3 @@
 for (var KEY = START; KEY < ARGUMENTS.length; KEY++) {
-  ARRAY[KEY] = ARGUMENTS[KEY];
+  ARRAY[ARRAY_KEY] = ARGUMENTS[KEY];
 }
diff --git a/lib/6to5/transformation/transformers/es6-rest-parameters.js b/lib/6to5/transformation/transformers/es6-rest-parameters.js
index a3d8e9a801..266b6f62f7 100644
--- a/lib/6to5/transformation/transformers/es6-rest-parameters.js
+++ b/lib/6to5/transformation/transformers/es6-rest-parameters.js
@@ -12,6 +12,14 @@ exports.Function = function (node, parent, file) {
   var argsId = t.identifier("arguments");
   argsId._ignoreAliasFunctions = true;
 
+  var start = t.literal(node.params.length);
+  var key = file.generateUidIdentifier("key");
+
+  var arrKey = key;
+  if (node.params.length) {
+    arrKey = t.binaryExpression("-", arrKey, start);
+  }
+
   node.body.body.unshift(
     t.variableDeclaration("var", [
       t.variableDeclarator(rest, t.arrayExpression([]))
@@ -19,9 +27,10 @@ exports.Function = function (node, parent, file) {
 
     util.template("rest", {
       ARGUMENTS: argsId,
-      START: t.literal(node.params.length),
+      ARRAY_KEY: arrKey,
+      START: start,
       ARRAY: rest,
-      KEY: file.generateUidIdentifier("key")
+      KEY: key
     })
   );
 };
diff --git a/test/fixtures/transformation/es6-rest-parameters/multiple/expected.js b/test/fixtures/transformation/es6-rest-parameters/multiple/expected.js
index 3aea58caf3..56ff1c407f 100644
--- a/test/fixtures/transformation/es6-rest-parameters/multiple/expected.js
+++ b/test/fixtures/transformation/es6-rest-parameters/multiple/expected.js
@@ -4,7 +4,7 @@ var t = function (f) {
   var items = [];
 
   for (var _key = 1; _key < arguments.length; _key++) {
-    items[_key] = arguments[_key];
+    items[_key - 1] = arguments[_key];
   }
 };
 
@@ -12,6 +12,6 @@ function t(f) {
   var items = [];
 
   for (var _key2 = 1; _key2 < arguments.length; _key2++) {
-    items[_key2] = arguments[_key2];
+    items[_key2 - 1] = arguments[_key2];
   }
 }