Fix object spread according to spec (#7034)

packages/babel-helpers/src/helpers.js

@@ -374,6 +374,26 @@ helpers.extends = defineHelper(`
   }
 `);
 
+helpers.objectSpread = defineHelper(`
+  import defineProperty from "defineProperty";
+
+  export default function _objectSpread(target) {
+    for (var i = 1; i < arguments.length; i++) {
+      var source = (arguments[i] != null) ? arguments[i] : {};
+      var ownKeys = Object.keys(source);
+      if (typeof Object.getOwnPropertySymbols === 'function') {
+        ownKeys = ownKeys.concat(Object.getOwnPropertySymbols(source).filter(function(sym) {
+          return Object.getOwnPropertyDescriptor(source, sym).enumerable;
+        }));
+      }
+      ownKeys.forEach(function(key) {
+        defineProperty(target, key, source[key]);
+      });
+    }
+    return target;
+  }
+`);
+
 helpers.get = defineHelper(`
   export default function _get(object, property, receiver) {
     if (object === null) object = Function.prototype;

packages/babel-plugin-proposal-object-rest-spread/README.md

@@ -54,18 +54,34 @@ require("@babel/core").transform("code", {
 
 ## Options
 
+By default, this plugin will produce spec compliant code. The Babel's `objectSpread` helper will be used.
+
+### `loose`
+
+`boolean`, defaults to `false`.
+
+Enabling this option will use Babel's `extends` helper, which is basically the same as `Object.assign` (see `useBuiltIns` below to use it directly).
+
+:warning: Please take in mind that even if they're almost equivalent, there's an important difference between spread and `Object.assign`: to summarize, **spread defines new properties, while `Object.assign()` sets them**, so using this mode might produce unexpected results in some case.
+
+For detailed information please check out [Spread VS. Object.assign](http://2ality.com/2016/10/rest-spread-properties.html#spreading-objects-versus-objectassign) and [Assigning VS. defining properties](http://exploringjs.com/es6/ch_oop-besides-classes.html#sec_assigning-vs-defining-properties).
+
+
 ### `useBuiltIns`
 
 `boolean`, defaults to `false`.
 
-By default, this plugin uses Babel's `extends` helper which polyfills `Object.assign`. Enabling this option will use `Object.assign` directly.
+Enabling this option will use `Object.assign` directly instead of the Babel's `extends` helper. Keep in mind that this flag only applies when `loose: true`.
+
+
+##### Example
 
 **.babelrc**
 
 ```json
 {
   "plugins": [
-    ["@babel/plugin-proposal-object-rest-spread", { "useBuiltIns": true }]
+    ["@babel/plugin-proposal-object-rest-spread", { "loose": true, "useBuiltIns": true }]
   ]
 }
 ```
@@ -86,3 +102,5 @@ z = Object.assign({ x }, y);
 
 * [Proposal: Object Rest/Spread Properties for ECMAScript](https://github.com/sebmarkbage/ecmascript-rest-spread)
 * [Spec](http://sebmarkbage.github.io/ecmascript-rest-spread)
+* [Spread VS. Object.assign](http://2ality.com/2016/10/rest-spread-properties.html#spreading-objects-versus-objectassign)
+* [Assigning VS. defining properties](http://exploringjs.com/es6/ch_oop-besides-classes.html#sec_assigning-vs-defining-properties)

packages/babel-plugin-proposal-object-rest-spread/src/index.js

@@ -2,9 +2,10 @@ import syntaxObjectRestSpread from "@babel/plugin-syntax-object-rest-spread";
 import { types as t } from "@babel/core";
 
 export default function(api, opts) {
-  const { useBuiltIns = false } = opts;
-  if (typeof useBuiltIns !== "boolean") {
-    throw new Error(".useBuiltIns must be a boolean, or undefined");
+  const { useBuiltIns = false, loose = false } = opts;
+
+  if (typeof loose !== "boolean") {
+    throw new Error(".loose must be a boolean, or undefined");
   }
 
   function hasRestElement(path) {
@@ -366,6 +367,10 @@ export default function(api, opts) {
           props = [];
         }
 
+        if (t.isSpreadElement(path.node.properties[0])) {
+          args.push(t.objectExpression([]));
+        }
+
         for (const prop of (path.node.properties: Array)) {
           if (t.isSpreadElement(prop)) {
             push();
@@ -377,14 +382,15 @@ export default function(api, opts) {
 
         push();
 
-        if (!t.isObjectExpression(args[0])) {
-          args.unshift(t.objectExpression([]));
+        let helper;
+        if (loose) {
+          helper = useBuiltIns
+            ? t.memberExpression(t.identifier("Object"), t.identifier("assign"))
+            : file.addHelper("extends");
+        } else {
+          helper = file.addHelper("objectSpread");
         }
 
-        const helper = useBuiltIns
-          ? t.memberExpression(t.identifier("Object"), t.identifier("assign"))
-          : file.addHelper("extends");
-
         path.replaceWith(t.callExpression(helper, args));
       },
     },

packages/babel-plugin-proposal-object-rest-spread/test/fixtures/object-spread/assignment/output.js

@@ -1,9 +1,11 @@
-function _extends() { _extends = Object.assign || function (target) { for (var i = 1; i < arguments.length; i++) { var source = arguments[i]; for (var key in source) { if (Object.prototype.hasOwnProperty.call(source, key)) { target[key] = source[key]; } } } return target; }; return _extends.apply(this, arguments); }
+function _objectSpread(target) { for (var i = 1; i < arguments.length; i++) { var source = arguments[i] != null ? arguments[i] : {}; var ownKeys = Object.keys(source); if (typeof Object.getOwnPropertySymbols === 'function') { ownKeys = ownKeys.concat(Object.getOwnPropertySymbols(source).filter(function (sym) { return Object.getOwnPropertyDescriptor(source, sym).enumerable; })); } ownKeys.forEach(function (key) { _defineProperty(target, key, source[key]); }); } return target; }
 
-z = _extends({
+function _defineProperty(obj, key, value) { if (key in obj) { Object.defineProperty(obj, key, { value: value, enumerable: true, configurable: true, writable: true }); } else { obj[key] = value; } return obj; }
+
+z = _objectSpread({
   x
 }, y);
 z = {
   x,
-  w: _extends({}, y)
+  w: _objectSpread({}, y)
 };

packages/babel-plugin-proposal-object-rest-spread/test/fixtures/object-spread/expression/input.js

@@ -1 +1,7 @@
 ({ x, ...y, a, ...b, c });
+
+({ ...Object.prototype });
+
+({ ...{ foo: 'bar' } });
+
+({ ...{ get foo () { return 'foo' } } });

packages/babel-plugin-proposal-object-rest-spread/test/fixtures/object-spread/expression/output.js

@@ -1,9 +1,24 @@
-function _extends() { _extends = Object.assign || function (target) { for (var i = 1; i < arguments.length; i++) { var source = arguments[i]; for (var key in source) { if (Object.prototype.hasOwnProperty.call(source, key)) { target[key] = source[key]; } } } return target; }; return _extends.apply(this, arguments); }
+function _objectSpread(target) { for (var i = 1; i < arguments.length; i++) { var source = arguments[i] != null ? arguments[i] : {}; var ownKeys = Object.keys(source); if (typeof Object.getOwnPropertySymbols === 'function') { ownKeys = ownKeys.concat(Object.getOwnPropertySymbols(source).filter(function (sym) { return Object.getOwnPropertyDescriptor(source, sym).enumerable; })); } ownKeys.forEach(function (key) { _defineProperty(target, key, source[key]); }); } return target; }
 
-_extends({
+function _defineProperty(obj, key, value) { if (key in obj) { Object.defineProperty(obj, key, { value: value, enumerable: true, configurable: true, writable: true }); } else { obj[key] = value; } return obj; }
+
+_objectSpread({
   x
 }, y, {
   a
 }, b, {
   c
 });
+
+_objectSpread({}, Object.prototype);
+
+_objectSpread({}, {
+  foo: 'bar'
+});
+
+_objectSpread({}, {
+  get foo() {
+    return 'foo';
+  }
+
+});

packages/babel-plugin-proposal-object-rest-spread/test/fixtures/object-spread/loose-mode-builtins/input.js

@@ -0,0 +1,3 @@
+z = { x, ...y };
+
+z = { x, w: { ...y } };

packages/babel-plugin-proposal-object-rest-spread/test/fixtures/object-spread/loose-mode-builtins/options.json

@@ -0,0 +1,5 @@
+{
+  "plugins": [
+    ["proposal-object-rest-spread", { "loose": true, "useBuiltIns": true }]
+  ]
+}

packages/babel-plugin-proposal-object-rest-spread/test/fixtures/object-spread/loose-mode-builtins/output.js

@@ -0,0 +1,7 @@
+z = Object.assign({
+  x
+}, y);
+z = {
+  x,
+  w: Object.assign({}, y)
+};

packages/babel-plugin-proposal-object-rest-spread/test/fixtures/object-spread/loose-mode/input.js

@@ -0,0 +1,3 @@
+z = { x, ...y };
+
+z = { x, w: { ...y } };

packages/babel-plugin-proposal-object-rest-spread/test/fixtures/object-spread/loose-mode/options.json

@@ -0,0 +1,5 @@
+{
+  "plugins": [
+    ["proposal-object-rest-spread", { "loose": true }]
+  ]
+}

packages/babel-plugin-proposal-object-rest-spread/test/fixtures/object-spread/loose-mode/output.js

@@ -0,0 +1,9 @@
+function _extends() { _extends = Object.assign || function (target) { for (var i = 1; i < arguments.length; i++) { var source = arguments[i]; for (var key in source) { if (Object.prototype.hasOwnProperty.call(source, key)) { target[key] = source[key]; } } } return target; }; return _extends.apply(this, arguments); }
+
+z = _extends({
+  x
+}, y);
+z = {
+  x,
+  w: _extends({}, y)
+};

packages/babel-plugin-proposal-object-rest-spread/test/fixtures/object-spread/no-object-assign-exec/exec.js

@@ -0,0 +1,40 @@
+Object.defineProperty(Object.prototype, 'NOSET', {
+  set(value) {
+    // noop
+  },
+});
+
+Object.defineProperty(Object.prototype, 'NOWRITE', {
+  writable: false,
+  value: 'abc',
+});
+
+const obj = { NOSET: 123 };
+// this wouldn't work as expected if transformed as Object.assign (or equivalent)
+// because those trigger object setters (spread don't)
+const objSpread = { ...obj };
+
+const obj2 = { NOSET: 123, NOWRITE: 456 };
+// this line would throw `TypeError: Cannot assign to read only property 'NOWRITE'`
+// if transformed as Object.assign (or equivalent) because those use *assignment* for creating properties
+// (spread defines them)
+const obj2Spread = { ...obj2 };
+
+assert.deepEqual(obj, objSpread);
+assert.deepEqual(obj2, obj2Spread);
+
+const KEY = Symbol('key');
+const obj3Spread = { ...{ get foo () { return 'bar' } }, [KEY]: 'symbol' };
+assert.equal(Object.getOwnPropertyDescriptor(obj3Spread, 'foo').value, 'bar');
+assert.equal(Object.getOwnPropertyDescriptor(obj3Spread, KEY).value, 'symbol');
+
+const obj4Spread = { ...Object.prototype };
+assert.isUndefined(Object.getOwnPropertyDescriptor(obj4Spread, 'hasOwnProperty'));
+
+assert.doesNotThrow(() => ({ ...null, ...undefined }));
+
+const o = Object.create(null);
+o.a = 'foo';
+o.__proto__ = [];
+const o2 = { ...o };
+assert.equal(false, Array.isArray(Object.getPrototypeOf(o2)));

packages/babel-plugin-proposal-object-rest-spread/test/fixtures/object-spread/variable-declaration/output.js

@@ -1,3 +1,5 @@
-function _extends() { _extends = Object.assign || function (target) { for (var i = 1; i < arguments.length; i++) { var source = arguments[i]; for (var key in source) { if (Object.prototype.hasOwnProperty.call(source, key)) { target[key] = source[key]; } } } return target; }; return _extends.apply(this, arguments); }
+function _objectSpread(target) { for (var i = 1; i < arguments.length; i++) { var source = arguments[i] != null ? arguments[i] : {}; var ownKeys = Object.keys(source); if (typeof Object.getOwnPropertySymbols === 'function') { ownKeys = ownKeys.concat(Object.getOwnPropertySymbols(source).filter(function (sym) { return Object.getOwnPropertyDescriptor(source, sym).enumerable; })); } ownKeys.forEach(function (key) { _defineProperty(target, key, source[key]); }); } return target; }
 
-var z = _extends({}, x);
+function _defineProperty(obj, key, value) { if (key in obj) { Object.defineProperty(obj, key, { value: value, enumerable: true, configurable: true, writable: true }); } else { obj[key] = value; } return obj; }
+
+var z = _objectSpread({}, x);

packages/babel-plugin-proposal-object-rest-spread/test/fixtures/useBuiltIns/assignment-invalid-option/input.js

@@ -1 +0,0 @@
-z = { x, ...y };

packages/babel-plugin-proposal-object-rest-spread/test/fixtures/useBuiltIns/assignment-invalid-option/options.json

@@ -1,4 +0,0 @@
-{
-  "plugins": [["proposal-object-rest-spread", { "useBuiltIns": "invalidOption" }]],
-  "throws": ".useBuiltIns must be a boolean, or undefined"
-}

packages/babel-plugin-proposal-object-rest-spread/test/fixtures/useBuiltIns/assignment-true/input.js

@@ -1 +0,0 @@
-z = { x, ...y };

packages/babel-plugin-proposal-object-rest-spread/test/fixtures/useBuiltIns/assignment-true/output.js

@@ -1,3 +0,0 @@
-z = Object.assign({
-  x
-}, y);

packages/babel-plugin-proposal-object-rest-spread/test/fixtures/useBuiltIns/options.json

@@ -1,3 +0,0 @@
-{
-  "plugins": [["proposal-object-rest-spread", { "useBuiltIns": true }]]
-}

packages/babel-preset-env/test/fixtures/preset-options/shippedProposals-use-builtins-entry/output.js

@@ -14,6 +14,10 @@ _AsyncGenerator.prototype.return = function (arg) { return this._invoke("return"
 
 function _AwaitValue(value) { this.wrapped = value; }
 
+function _objectSpread(target) { for (var i = 1; i < arguments.length; i++) { var source = arguments[i] != null ? arguments[i] : {}; var ownKeys = Object.keys(source); if (typeof Object.getOwnPropertySymbols === 'function') { ownKeys = ownKeys.concat(Object.getOwnPropertySymbols(source).filter(function (sym) { return Object.getOwnPropertyDescriptor(source, sym).enumerable; })); } ownKeys.forEach(function (key) { _defineProperty(target, key, source[key]); }); } return target; }
+
+function _defineProperty(obj, key, value) { if (key in obj) { Object.defineProperty(obj, key, { value: value, enumerable: true, configurable: true, writable: true }); } else { obj[key] = value; } return obj; }
+
 function _objectWithoutProperties(source, excluded) { if (source == null) return {}; var target = {}; var sourceKeys = Object.keys(source); var key, i; for (i = 0; i < sourceKeys.length; i++) { key = sourceKeys[i]; if (excluded.indexOf(key) >= 0) continue; target[key] = source[key]; } if (Object.getOwnPropertySymbols) { var sourceSymbolKeys = Object.getOwnPropertySymbols(source); for (i = 0; i < sourceSymbolKeys.length; i++) { key = sourceSymbolKeys[i]; if (excluded.indexOf(key) >= 0) continue; if (!Object.prototype.propertyIsEnumerable.call(source, key)) continue; target[key] = source[key]; } } return target; }
 
 var _x$y$a$b = {
@@ -26,7 +30,7 @@ var _x$y$a$b = {
     y = _x$y$a$b.y,
     z = _objectWithoutProperties(_x$y$a$b, ["x", "y"]);
 
-var n = Object.assign({
+var n = _objectSpread({
   x: x,
   y: y
 }, z);

packages/babel-preset-env/test/fixtures/preset-options/shippedProposals-use-builtins-usage/output.js

@@ -6,9 +6,11 @@ require("core-js/modules/es6.symbol");
 
 require("core-js/modules/es6.promise");
 
-require("core-js/modules/es6.array.index-of");
+require("core-js/modules/es6.array.for-each");
 
-require("core-js/modules/es6.object.assign");
+require("core-js/modules/es6.array.filter");
+
+require("core-js/modules/es6.array.index-of");
 
 function _awaitAsyncGenerator(value) { return new _AwaitValue(value); }
 
@@ -26,6 +28,10 @@ _AsyncGenerator.prototype.return = function (arg) { return this._invoke("return"
 
 function _AwaitValue(value) { this.wrapped = value; }
 
+function _objectSpread(target) { for (var i = 1; i < arguments.length; i++) { var source = arguments[i] != null ? arguments[i] : {}; var ownKeys = Object.keys(source); if (typeof Object.getOwnPropertySymbols === 'function') { ownKeys = ownKeys.concat(Object.getOwnPropertySymbols(source).filter(function (sym) { return Object.getOwnPropertyDescriptor(source, sym).enumerable; })); } ownKeys.forEach(function (key) { _defineProperty(target, key, source[key]); }); } return target; }
+
+function _defineProperty(obj, key, value) { if (key in obj) { Object.defineProperty(obj, key, { value: value, enumerable: true, configurable: true, writable: true }); } else { obj[key] = value; } return obj; }
+
 function _objectWithoutProperties(source, excluded) { if (source == null) return {}; var target = {}; var sourceKeys = Object.keys(source); var key, i; for (i = 0; i < sourceKeys.length; i++) { key = sourceKeys[i]; if (excluded.indexOf(key) >= 0) continue; target[key] = source[key]; } if (Object.getOwnPropertySymbols) { var sourceSymbolKeys = Object.getOwnPropertySymbols(source); for (i = 0; i < sourceSymbolKeys.length; i++) { key = sourceSymbolKeys[i]; if (excluded.indexOf(key) >= 0) continue; if (!Object.prototype.propertyIsEnumerable.call(source, key)) continue; target[key] = source[key]; } } return target; }
 
 var _x$y$a$b = {
@@ -38,7 +44,7 @@ var _x$y$a$b = {
     y = _x$y$a$b.y,
     z = _objectWithoutProperties(_x$y$a$b, ["x", "y"]);
 
-var n = Object.assign({
+var n = _objectSpread({
   x: x,
   y: y
 }, z);

packages/babel-preset-env/test/fixtures/preset-options/shippedProposals/output.js

@@ -14,7 +14,9 @@ _AsyncGenerator.prototype.return = function (arg) { return this._invoke("return"
 
 function _AwaitValue(value) { this.wrapped = value; }
 
-function _extends() { _extends = Object.assign || function (target) { for (var i = 1; i < arguments.length; i++) { var source = arguments[i]; for (var key in source) { if (Object.prototype.hasOwnProperty.call(source, key)) { target[key] = source[key]; } } } return target; }; return _extends.apply(this, arguments); }
+function _objectSpread(target) { for (var i = 1; i < arguments.length; i++) { var source = arguments[i] != null ? arguments[i] : {}; var ownKeys = Object.keys(source); if (typeof Object.getOwnPropertySymbols === 'function') { ownKeys = ownKeys.concat(Object.getOwnPropertySymbols(source).filter(function (sym) { return Object.getOwnPropertyDescriptor(source, sym).enumerable; })); } ownKeys.forEach(function (key) { _defineProperty(target, key, source[key]); }); } return target; }
+
+function _defineProperty(obj, key, value) { if (key in obj) { Object.defineProperty(obj, key, { value: value, enumerable: true, configurable: true, writable: true }); } else { obj[key] = value; } return obj; }
 
 function _objectWithoutProperties(source, excluded) { if (source == null) return {}; var target = {}; var sourceKeys = Object.keys(source); var key, i; for (i = 0; i < sourceKeys.length; i++) { key = sourceKeys[i]; if (excluded.indexOf(key) >= 0) continue; target[key] = source[key]; } if (Object.getOwnPropertySymbols) { var sourceSymbolKeys = Object.getOwnPropertySymbols(source); for (i = 0; i < sourceSymbolKeys.length; i++) { key = sourceSymbolKeys[i]; if (excluded.indexOf(key) >= 0) continue; if (!Object.prototype.propertyIsEnumerable.call(source, key)) continue; target[key] = source[key]; } } return target; }
 
@@ -28,7 +30,7 @@ var _x$y$a$b = {
     y = _x$y$a$b.y,
     z = _objectWithoutProperties(_x$y$a$b, ["x", "y"]);
 
-var n = _extends({
+var n = _objectSpread({
   x: x,
   y: y
 }, z);