deopt rest parameter member expression optimisation on child arrow functions - fixes #1631

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

@@ -9,6 +9,13 @@ var memberExpressionOptimisationVisitor = {
       return this.skip();
     }
 
+    var stop = () => {
+      state.canOptimise = false;
+      this.stop();
+    };
+
+    if (this.isArrowFunctionExpression()) return stop();
+
     // skip over functions as whatever `arguments` we reference inside will refer
     // to the wrong function
     if (this.isFunctionDeclaration() || this.isFunctionExpression()) {
@@ -31,8 +38,7 @@ var memberExpressionOptimisationVisitor = {
       }
     }
 
-    state.canOptimise = false;
-    this.stop();
+    stop();
   }
 };
 
@@ -90,8 +96,7 @@ export function Func/*tion*/(node, parent, scope, file) {
 
   // we only have shorthands and there's no other references
   if (state.canOptimise && state.candidates.length) {
-    for (var i = 0; i < state.candidates.length; i++) {
-      var candidate = state.candidates[i];
+    for (var candidate of (state.candidates: Array)) {
       candidate.replaceWith(argsId);
       optimizeMemberExpression(candidate.parent, node.params.length);
     }

test/core/fixtures/transformation/es6.parameters.rest/arrow-functions/actual.js

@@ -1,19 +1,25 @@
 var concat = (...arrs) => {
-    var x = arrs[0];
-    var y = arrs[1];
+  var x = arrs[0];
+  var y = arrs[1];
 };
 
 var somefun = function () {
-    let get2ndArg = (a, b, ...args1) => {
-        var _b = args1[0];
-        let somef = (x, y, z, ...args2) => {
-            var _a = args2[0];
-        };
-        let somefg = (c, d, e, f, ...args3) => {
-            var _a = args3[0];
-        };
-        var _c = arguments[1];
-        var _d = args1[1];
+  let get2ndArg = (a, b, ...args1) => {
+    var _b = args1[0];
+    let somef = (x, y, z, ...args2) => {
+      var _a = args2[0];
     };
-    let get1stArg = (...args) => args[0];
+    let somefg = (c, d, e, f, ...args3) => {
+      var _a = args3[0];
+    };
+    var _c = arguments[1];
+    var _d = args1[1];
+  };
+  let get1stArg = (...args) => args[0];
+}
+
+function demo1(...args) {
+  return (i) => {
+    return args[i+0];
+  };
 }

test/core/fixtures/transformation/es6.parameters.rest/arrow-functions/expected.js

@@ -1,26 +1,39 @@
 "use strict";
 
 var concat = function concat() {
-    var x = arguments[0];
-    var y = arguments[1];
+  var x = arguments[0];
+  var y = arguments[1];
 };
 
 var somefun = function somefun() {
-    var _arguments = arguments;
+  var _arguments = arguments;
 
-    var get2ndArg = function get2ndArg(a, b) {
-        var _b = arguments[2];
-        var somef = function somef(x, y, z) {
-            var _a = arguments[3];
-        };
-        var somefg = function somefg(c, d, e, f) {
-            var _a = arguments[4];
-        };
-        var _c = _arguments[1];
-        var _d = arguments[3];
+  var get2ndArg = function get2ndArg(a, b) {
+    for (var _len = arguments.length, args1 = Array(_len > 2 ? _len - 2 : 0), _key = 2; _key < _len; _key++) {
+      args1[_key - 2] = arguments[_key];
+    }
+
+    var _b = args1[0];
+    var somef = function somef(x, y, z) {
+      var _a = arguments[3];
     };
-    var get1stArg = function get1stArg() {
-        return arguments[0];
+    var somefg = function somefg(c, d, e, f) {
+      var _a = arguments[4];
     };
+    var _c = _arguments[1];
+    var _d = args1[1];
+  };
+  var get1stArg = function get1stArg() {
+    return arguments[0];
+  };
 };
 
+function demo1() {
+  for (var _len2 = arguments.length, args = Array(_len2), _key2 = 0; _key2 < _len2; _key2++) {
+    args[_key2] = arguments[_key2];
+  }
+
+  return function (i) {
+    return args[i + 0];
+  };
+}