Add "allowArrayLike" support to the for-of transform

packages/babel-helpers/src/helpers.js

@@ -1009,10 +1009,13 @@ helpers.createForOfIteratorHelper = helper("7.9.0")`
   // e: error (called whenever something throws)
   // f: finish (always called at the end)
 
-  export default function _createForOfIteratorHelper(o) {
+  export default function _createForOfIteratorHelper(o, allowArrayLike) {
     if (typeof Symbol === "undefined" || o[Symbol.iterator] == null) {
       // Fallback for engines without symbol support
-      if (Array.isArray(o)) {
+      if (
+        Array.isArray(o) ||
+        (allowArrayLike && o && typeof o.length === "number")
+      ) {
         var i = 0;
         var F = function(){};
         return {
@@ -1056,12 +1059,15 @@ helpers.createForOfIteratorHelper = helper("7.9.0")`
 `;
 
 helpers.createForOfIteratorHelperLoose = helper("7.9.0")`
-  export default function _createForOfIteratorHelperLoose(o) {
+  export default function _createForOfIteratorHelperLoose(o, allowArrayLike) {
     var i = 0;
 
     if (typeof Symbol === "undefined" || o[Symbol.iterator] == null) {
       // Fallback for engines without symbol support
-      if (Array.isArray(o))
+      if (
+        Array.isArray(o) ||
+        (allowArrayLike && o && typeof o.length === "number")
+      )
         return function() {
           if (i >= o.length) return { done: true };
           return { done: false, value: o[i++] };

packages/babel-plugin-transform-for-of/src/index.js

@@ -4,14 +4,20 @@ import { template, types as t } from "@babel/core";
 export default declare((api, options) => {
   api.assertVersion(7);
 
-  const { loose, assumeArray } = options;
+  const { loose, assumeArray, allowArrayLike } = options;
 
   if (loose === true && assumeArray === true) {
     throw new Error(
       `The loose and assumeArray options cannot be used together in @babel/plugin-transform-for-of`,
     );
   }
 
+  if (assumeArray === true && allowArrayLike === true) {
+    throw new Error(
+      `The assumeArray and allowArrayLike options cannot be used together in @babel/plugin-transform-for-of`,
+    );
+  }
+
   if (assumeArray) {
     return {
       name: "transform-for-of",
@@ -84,12 +90,12 @@ export default declare((api, options) => {
   `);
 
   const buildForOfLoose = template.statements(`
-    for (var ITERATOR_HELPER = CREATE_ITERATOR_HELPER(OBJECT), STEP_KEY;
+    for (var ITERATOR_HELPER = CREATE_ITERATOR_HELPER(OBJECT, ALLOW_ARRAY_LIKE), STEP_KEY;
         !(STEP_KEY = ITERATOR_HELPER()).done;) BODY;
   `);
 
   const buildForOf = template.statements(`
-    var ITERATOR_HELPER = CREATE_ITERATOR_HELPER(OBJECT), STEP_KEY;
+    var ITERATOR_HELPER = CREATE_ITERATOR_HELPER(OBJECT, ALLOW_ARRAY_LIKE), STEP_KEY;
     try {
       for (ITERATOR_HELPER.s(); !(STEP_KEY = ITERATOR_HELPER.n()).done;) BODY;
     } catch (err) {
@@ -202,6 +208,7 @@ export default declare((api, options) => {
         const nodes = builder.build({
           CREATE_ITERATOR_HELPER: state.addHelper(builder.helper),
           ITERATOR_HELPER: scope.generateUidIdentifier("iteratorHelper"),
+          ALLOW_ARRAY_LIKE: allowArrayLike ? t.booleanLiteral(true) : null,
           STEP_KEY: t.identifier(stepKey),
           OBJECT: node.right,
           BODY: node.body,

packages/babel-plugin-transform-for-of/test/fixtures/loose-allowArrayLike/holes/exec.js

@@ -0,0 +1,7 @@
+var p2 = { 0: "a", 2: "c", length: 3 };
+
+var arr = [];
+for (var x of p2) arr.push(x);
+
+expect(arr).toEqual(["a", undefined, "c"]);
+expect(1 in arr).toBe(true); // Not holey

packages/babel-plugin-transform-for-of/test/fixtures/loose-allowArrayLike/holes/options.json

@@ -0,0 +1,6 @@
+{
+  "plugins": [
+    ["external-helpers", { "helperVersion": "7.100.0" }],
+    ["transform-for-of", { "loose": true, "allowArrayLike": true }]
+  ]
+}

packages/babel-plugin-transform-for-of/test/fixtures/loose-allowArrayLike/length-cropped/exec.js

@@ -0,0 +1,6 @@
+var p2 = { 0: "b", 1: "c", 2: "d", length: 2 };
+
+var arr = [];
+for (var x of p2) arr.push(x);
+
+expect(arr).toEqual(["b", "c"]);

packages/babel-plugin-transform-for-of/test/fixtures/loose-allowArrayLike/length-cropped/options.json

@@ -0,0 +1,6 @@
+{
+  "plugins": [
+    ["external-helpers", { "helperVersion": "7.100.0" }],
+    ["transform-for-of", { "loose": true, "allowArrayLike": true }]
+  ]
+}

packages/babel-plugin-transform-for-of/test/fixtures/loose-allowArrayLike/simple/exec.js

@@ -0,0 +1,6 @@
+var p2 = { 0: "b", 1: "c", 2: "d", length: 3 };
+
+var arr = [];
+for (var x of p2) arr.push(x);
+
+expect(arr).toEqual(["b", "c", "d"]);

packages/babel-plugin-transform-for-of/test/fixtures/loose-allowArrayLike/simple/input.js

@@ -0,0 +1 @@
+for (var x of p2) arr.push(x);

packages/babel-plugin-transform-for-of/test/fixtures/loose-allowArrayLike/simple/options.json

@@ -0,0 +1,6 @@
+{
+  "plugins": [
+    ["external-helpers", { "helperVersion": "7.100.0" }],
+    ["transform-for-of", { "loose": true, "allowArrayLike": true }]
+  ]
+}

packages/babel-plugin-transform-for-of/test/fixtures/loose-allowArrayLike/simple/output.js

@@ -0,0 +1,4 @@
+for (var _iteratorHelper = babelHelpers.createForOfIteratorHelperLoose(p2, true), _step; !(_step = _iteratorHelper()).done;) {
+  var x = _step.value;
+  arr.push(x);
+}

packages/babel-plugin-transform-for-of/test/fixtures/spec-allowArrayLike/holes/exec.js

@@ -0,0 +1,7 @@
+var p2 = { 0: "a", 2: "c", length: 3 };
+
+var arr = [];
+for (var x of p2) arr.push(x);
+
+expect(arr).toEqual(["a", undefined, "c"]);
+expect(1 in arr).toBe(true); // Not holey

packages/babel-plugin-transform-for-of/test/fixtures/spec-allowArrayLike/holes/options.json

@@ -0,0 +1,6 @@
+{
+  "plugins": [
+    ["external-helpers", { "helperVersion": "7.100.0" }],
+    ["transform-for-of", { "allowArrayLike": true }]
+  ]
+}

packages/babel-plugin-transform-for-of/test/fixtures/spec-allowArrayLike/length-cropped/exec.js

@@ -0,0 +1,6 @@
+var p2 = { 0: "b", 1: "c", 2: "d", length: 2 };
+
+var arr = [];
+for (var x of p2) arr.push(x);
+
+expect(arr).toEqual(["b", "c"]);

packages/babel-plugin-transform-for-of/test/fixtures/spec-allowArrayLike/length-cropped/options.json

@@ -0,0 +1,6 @@
+{
+  "plugins": [
+    ["external-helpers", { "helperVersion": "7.100.0" }],
+    ["transform-for-of", { "allowArrayLike": true }]
+  ]
+}

packages/babel-plugin-transform-for-of/test/fixtures/spec-allowArrayLike/simple/exec.js

@@ -0,0 +1,6 @@
+var p2 = { 0: "b", 1: "c", 2: "d", length: 3 };
+
+var arr = [];
+for (var x of p2) arr.push(x);
+
+expect(arr).toEqual(["b", "c", "d"]);

packages/babel-plugin-transform-for-of/test/fixtures/spec-allowArrayLike/simple/input.js

@@ -0,0 +1 @@
+for (var x of p2) arr.push(x);

packages/babel-plugin-transform-for-of/test/fixtures/spec-allowArrayLike/simple/options.json

@@ -0,0 +1,6 @@
+{
+  "plugins": [
+    ["external-helpers", { "helperVersion": "7.100.0" }],
+    ["transform-for-of", { "allowArrayLike": true }]
+  ]
+}

packages/babel-plugin-transform-for-of/test/fixtures/spec-allowArrayLike/simple/output.js

@@ -0,0 +1,13 @@
+var _iteratorHelper = babelHelpers.createForOfIteratorHelper(p2, true),
+    _step;
+
+try {
+  for (_iteratorHelper.s(); !(_step = _iteratorHelper.n()).done;) {
+    var x = _step.value;
+    arr.push(x);
+  }
+} catch (err) {
+  _iteratorHelper.e(err);
+} finally {
+  _iteratorHelper.f();
+}

packages/babel-preset-env/test/fixtures/sanity/block-scoping-for-of/output.js

@@ -6,7 +6,7 @@ function _iterableToArrayLimit(arr, i) { if (!(Symbol.iterator in Object(arr) ||
 
 function _arrayWithHoles(arr) { if (Array.isArray(arr)) return arr; }
 
-function _createForOfIteratorHelper(o) { if (typeof Symbol === "undefined" || o[Symbol.iterator] == null) throw new TypeError("Invalid attempt to iterate non-iterable instance.\nIn order to be iterable, non-array objects must have a [Symbol.iterator]() method."); var it, normalCompletion = true, didErr = false, err; return { s: function s() { it = o[Symbol.iterator](); }, n: function n() { var step = it.next(); normalCompletion = step.done; return step; }, e: function e(_e) { didErr = true; err = _e; }, f: function f() { try { if (!normalCompletion && it["return"] != null) it["return"](); } finally { if (didErr) throw err; } } }; }
+function _createForOfIteratorHelper(o, allowArrayLike) { if (typeof Symbol === "undefined" || o[Symbol.iterator] == null) { if (Array.isArray(o) || allowArrayLike && o && typeof o.length === "number") { var i = 0; var F = function F() {}; return { s: F, n: function n() { if (i >= o.length) return { done: true }; return { done: false, value: o[i++] }; }, e: F, f: F }; } throw new TypeError("Invalid attempt to iterate non-iterable instance.\nIn order to be iterable, non-array objects must have a [Symbol.iterator]() method."); } var it, normalCompletion = true, didErr = false, err; return { s: function s() { it = o[Symbol.iterator](); }, n: function n() { var step = it.next(); normalCompletion = step.done; return step; }, e: function e(_e) { didErr = true; err = _e; }, f: function f() { try { if (!normalCompletion && it["return"] != null) it["return"](); } finally { if (didErr) throw err; } } }; }
 
 // https://github.com/babel/babel/issues/7557
 var _iteratorHelper = _createForOfIteratorHelper(c),