Improve array destructuring spec compliance

packages/babel-helpers/src/helpers.ts

@@ -788,7 +788,13 @@ helpers.iterableToArrayLimit = helper("7.0.0-beta.0")`
     var _d = false;
     var _s, _e;
     try {
-      for (_i = _i.call(arr); !(_n = (_s = _i.next()).done); _n = true) {
+      _i = _i.call(arr);
+      if (i === 0) {
+        if (typeof _i !== "object" && typeof _i !== "function") return;
+        _n = false;
+        return _arr;
+      }
+      for (; !(_n = (_s = _i.next()).done); _n = true) {
         _arr.push(_s.value);
         if (i && _arr.length === i) break;
       }
@@ -812,8 +818,13 @@ helpers.iterableToArrayLimitLoose = helper("7.0.0-beta.0")`
     if (_i == null) return;
 
     var _arr = [];
-    for (_i = _i.call(arr), _step; !(_step = _i.next()).done;) {
-      _arr.push(_step.value);
+    _i = _i.call(arr);
+    if (i === 0) {
+      if (typeof _i !== "object" && typeof _i !== "function") return;
+      return _arr;
+    }
+    for (var _s; !(_s = _i.next()).done;) {
+      _arr.push(_s.value);
       if (i && _arr.length === i) break;
     }
     return _arr;

packages/babel-plugin-transform-destructuring/test/fixtures/destructuring/empty-array-pattern/exec.js

@@ -0,0 +1,36 @@
+expect(function () {
+  var [] = null;
+}).toThrow("Invalid attempt to destructure non-iterable instance.\nIn order to be iterable, non-array objects must have a [Symbol.iterator]() method.");
+
+expect(function () {
+  var [] = 42;
+}).toThrow("Invalid attempt to destructure non-iterable instance.\nIn order to be iterable, non-array objects must have a [Symbol.iterator]() method.");
+
+expect(function () {
+  var [] = {};
+}).toThrow("Invalid attempt to destructure non-iterable instance.\nIn order to be iterable, non-array objects must have a [Symbol.iterator]() method.");
+
+expect(function () {
+  var [] = { [Symbol.iterator]: function() {} };
+}).toThrow("Invalid attempt to destructure non-iterable instance.\nIn order to be iterable, non-array objects must have a [Symbol.iterator]() method.");
+
+var [] = [];
+var [] = [0, 1, 2];
+var [] = "foo";
+var [] = (function*() { throw new Error("Should not throw"); })();
+var [] = { [Symbol.iterator]: function() { return {}; } }
+var [] = { [Symbol.iterator]: function() { return function() {}; } }
+var [] = { [Symbol.iterator]: async function*() {} }
+
+var returnCalled = false;
+var [] = {
+  [Symbol.iterator]: function() {
+    return {
+      return: function() {
+        returnCalled = true;
+        return {};
+      }
+    };
+  }
+};
+expect(returnCalled).toStrictEqual(true);

packages/babel-plugin-transform-destructuring/test/fixtures/destructuring/empty-array-pattern/input.js

@@ -0,0 +1,24 @@
+var [] = null;
+var [] = 42;
+var [] = {};
+var [] = { [Symbol.iterator]: function() {} };
+
+var [] = [];
+var [] = [0, 1, 2];
+var [] = "foo";
+var [] = (function*() { throw new Error("Should not throw"); })();
+var [] = { [Symbol.iterator]: function() { return {}; } }
+var [] = { [Symbol.iterator]: function() { return function() {}; } }
+var [] = { [Symbol.iterator]: async function*() {} }
+
+var returnCalled = false;
+var [] = {
+  [Symbol.iterator]: function() {
+    return {
+      return: function() {
+        returnCalled = true;
+        return {};
+      }
+    };
+  }
+};

packages/babel-plugin-transform-destructuring/test/fixtures/destructuring/empty-array-pattern/output.js

@@ -0,0 +1,65 @@
+var _ref = null,
+  _ref2 = babelHelpers.slicedToArray(_ref, 0);
+var _ = 42,
+  _ref3 = babelHelpers.slicedToArray(_, 0);
+var _ref4 = {},
+  _ref5 = babelHelpers.slicedToArray(_ref4, 0);
+var _Symbol$iterator = {
+    [Symbol.iterator]: function () {}
+  },
+  _Symbol$iterator2 = babelHelpers.slicedToArray(_Symbol$iterator, 0);
+var _ref6 = [0, 1, 2];
+var _foo = "foo",
+  _foo2 = babelHelpers.slicedToArray(_foo, 0);
+var _ref7 = /*#__PURE__*/babelHelpers.regeneratorRuntime().mark(function _callee() {
+    return babelHelpers.regeneratorRuntime().wrap(function _callee$(_context) {
+      while (1) {
+        switch (_context.prev = _context.next) {
+          case 0:
+            throw new Error("Should not throw");
+          case 1:
+          case "end":
+            return _context.stop();
+        }
+      }
+    }, _callee);
+  })(),
+  _ref8 = babelHelpers.slicedToArray(_ref7, 0);
+var _Symbol$iterator3 = {
+    [Symbol.iterator]: function () {
+      return {};
+    }
+  },
+  _Symbol$iterator4 = babelHelpers.slicedToArray(_Symbol$iterator3, 0);
+var _Symbol$iterator5 = {
+    [Symbol.iterator]: function () {
+      return function () {};
+    }
+  },
+  _Symbol$iterator6 = babelHelpers.slicedToArray(_Symbol$iterator5, 0);
+var _Symbol$iterator7 = {
+    [Symbol.iterator]: /*#__PURE__*/babelHelpers.regeneratorRuntime().mark(function _callee2() {
+      return babelHelpers.regeneratorRuntime().async(function _callee2$(_context2) {
+        while (1) {
+          switch (_context2.prev = _context2.next) {
+            case 0:
+            case "end":
+              return _context2.stop();
+          }
+        }
+      }, _callee2, null, null, Promise);
+    })
+  },
+  _Symbol$iterator8 = babelHelpers.slicedToArray(_Symbol$iterator7, 0);
+var returnCalled = false;
+var _Symbol$iterator9 = {
+    [Symbol.iterator]: function () {
+      return {
+        return: function () {
+          returnCalled = true;
+          return {};
+        }
+      };
+    }
+  },
+  _Symbol$iterator10 = babelHelpers.slicedToArray(_Symbol$iterator9, 0);

packages/babel-plugin-transform-destructuring/test/fixtures/destructuring/init-hole/output.js

@@ -45,7 +45,7 @@ try {
 expect(thrown).toEqual(true);
 try {
   thrown = false;
-  var _ = babelHelpers.toArray(void 0);
+  var _ = babelHelpers.slicedToArray(void 0, 0);
 } catch (e) {
   thrown = true;
 }

packages/babel-preset-env/test/fixtures/plugins-integration/issue-15012/output.js

@@ -1,5 +1,5 @@
 function f(_ref) {
-  var _ref2 = babelHelpers.toArray(_ref);
+  var _ref2 = babelHelpers.slicedToArray(_ref, 0);
   return /*#__PURE__*/babelHelpers.regeneratorRuntime().mark(function _callee() {
     return babelHelpers.regeneratorRuntime().wrap(function _callee$(_context) {
       while (1) {

packages/babel-traverse/src/scope/index.ts

@@ -686,7 +686,7 @@ export default class Scope {
     if (i === true) {
       // Used in array-spread to create an array.
       helperName = "toConsumableArray";
-    } else if (i) {
+    } else if (typeof i === "number") {
       args.push(numericLiteral(i));
 
       // Used in array-rest to create an array from a subset of an iterable.