Improve array destructuring spec compliance

packages/babel-helpers/src/helpers.ts

@@ -779,25 +779,36 @@ helpers.iterableToArrayLimit = helper("7.0.0-beta.0")`
     // _e = _iteratorError
     // _i = _iterator
     // _s = _step
+    // _x = _next
+    // _r = _return
 
     var _i = arr == null ? null : (typeof Symbol !== "undefined" && arr[Symbol.iterator] || arr["@@iterator"]);
     if (_i == null) return;
 
     var _arr = [];
     var _n = true;
     var _d = false;
-    var _s, _e;
+    var _s, _e, _x, _r;
     try {
-      for (_i = _i.call(arr); !(_n = (_s = _i.next()).done); _n = true) {
-        _arr.push(_s.value);
-        if (i && _arr.length === i) break;
+      _x = (_i = _i.call(arr)).next;
+      if (i === 0) {
+        if (Object(_i) !== _i) return;
+        _n = false;
+      } else {
+        for (; !(_n = (_s = _x.call(_i)).done); _n = true) {
+          _arr.push(_s.value);
+          if(_arr.length === i) break;
+        }
       }
     } catch (err) {
       _d = true;
       _e = err;
     } finally {
       try {
-        if (!_n && _i["return"] != null) _i["return"]();
+        if (!_n && _i["return"] != null) {
+          _r = _i["return"]();
+          if (Object(_r) !== _r) return;
+        }
       } finally {
         if (_d) throw _e;
       }
@@ -812,9 +823,9 @@ 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);
-      if (i && _arr.length === i) break;
+    var _s;
+    for (_i = _i.call(arr); arr.length < i && !(_s = _i.next()).done; ) {
+      _arr.push(_s.value);
     }
     return _arr;
   }

packages/babel-plugin-transform-destructuring/test/fixtures/destructuring/check-iterator-return/exec.js

@@ -0,0 +1,41 @@
+expect(() => {
+  var [] = {
+    [Symbol.iterator]: () => {
+      return {
+        return: () => {},
+      };
+    },
+  };
+}).toThrow(TypeError);
+
+expect(() => {
+  var [] = {
+    [Symbol.iterator]: () => {
+      return {
+        return: () => ({}),
+      };
+    },
+  };
+}).not.toThrow();
+
+expect(() => {
+  var [x] = {
+    [Symbol.iterator]: () => {
+      return {
+        next: () => ({ done: false, value: 1 }),
+        return: () => {},
+      };
+    },
+  };
+}).toThrow(TypeError);
+
+expect(() => {
+  var [x] = {
+    [Symbol.iterator]: () => {
+      return {
+        next: () => ({ done: false, value: 1 }),
+        return: () => ({}),
+      };
+    },
+  };
+}).not.toThrow();

packages/babel-plugin-transform-destructuring/test/fixtures/destructuring/check-iterator-return/input.js

@@ -0,0 +1,33 @@
+var [] = {
+  [Symbol.iterator]: () => {
+    return {
+      return: () => {},
+    };
+  },
+};
+
+var [] = {
+  [Symbol.iterator]: () => {
+    return {
+      return: () => ({}),
+    };
+  },
+};
+
+var [x] = {
+  [Symbol.iterator]: () => {
+    return {
+      next: () => ({ done: false, value: 1 }),
+      return: () => {},
+    };
+  },
+};
+
+var [x] = {
+  [Symbol.iterator]: () => {
+    return {
+      next: () => ({ done: false, value: 1 }),
+      return: () => ({}),
+    };
+  },
+};

packages/babel-plugin-transform-destructuring/test/fixtures/destructuring/check-iterator-return/output.js

@@ -0,0 +1,42 @@
+var _Symbol$iterator = {
+    [Symbol.iterator]: () => {
+      return {
+        return: () => {}
+      };
+    }
+  },
+  _Symbol$iterator2 = babelHelpers.slicedToArray(_Symbol$iterator, 0);
+var _Symbol$iterator3 = {
+    [Symbol.iterator]: () => {
+      return {
+        return: () => ({})
+      };
+    }
+  },
+  _Symbol$iterator4 = babelHelpers.slicedToArray(_Symbol$iterator3, 0);
+var _Symbol$iterator5 = {
+    [Symbol.iterator]: () => {
+      return {
+        next: () => ({
+          done: false,
+          value: 1
+        }),
+        return: () => {}
+      };
+    }
+  },
+  _Symbol$iterator6 = babelHelpers.slicedToArray(_Symbol$iterator5, 1),
+  x = _Symbol$iterator6[0];
+var _Symbol$iterator7 = {
+    [Symbol.iterator]: () => {
+      return {
+        next: () => ({
+          done: false,
+          value: 1
+        }),
+        return: () => ({})
+      };
+    }
+  },
+  _Symbol$iterator8 = babelHelpers.slicedToArray(_Symbol$iterator7, 1),
+  x = _Symbol$iterator8[0];

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

@@ -0,0 +1,38 @@
+expect(() => {
+  var [] = null;
+}).toThrow(TypeError);
+
+expect(() => {
+  var [] = 42;
+}).toThrow(TypeError);
+
+expect(() => {
+  var [] = {};
+}).toThrow(TypeError);
+
+expect(() => {
+  var [] = { [Symbol.iterator]: () => {} };
+}).toThrow(TypeError);
+
+expect(() => {
+  var [] = [];
+  var [] = [0, 1, 2];
+  var [] = "foo";
+  var [] = (function*() { throw new Error("Should not throw"); })();
+  var [] = { [Symbol.iterator]: () => ({}) };
+  var [] = { [Symbol.iterator]: () => () => {} };
+  var [] = { [Symbol.iterator]: async function*() {} };
+}).not.toThrow();
+
+var returnCalled = false;
+var [] = {
+  [Symbol.iterator]: () => {
+    return {
+      return: () => {
+        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]: () => {} };
+
+var [] = [];
+var [] = [0, 1, 2];
+var [] = "foo";
+var [] = (function*() { throw new Error("Should not throw"); })();
+var [] = { [Symbol.iterator]: () => ({}) };
+var [] = { [Symbol.iterator]: () => () => {} };
+var [] = { [Symbol.iterator]: async function*() {} };
+
+var returnCalled = false;
+var [] = {
+  [Symbol.iterator]: () => {
+    return {
+      return: () => {
+        returnCalled = true;
+        return {};
+      },
+    };
+  },
+};

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

@@ -0,0 +1,61 @@
+var _ref = null,
+  _ref2 = babelHelpers.slicedToArray(_ref, 0);
+var _ = 42,
+  _ref3 = babelHelpers.slicedToArray(_, 0);
+var _ref4 = {},
+  _ref5 = babelHelpers.slicedToArray(_ref4, 0);
+var _Symbol$iterator = {
+    [Symbol.iterator]: () => {}
+  },
+  _Symbol$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$iterator3 = {
+    [Symbol.iterator]: () => ({})
+  },
+  _Symbol$iterator4 = babelHelpers.slicedToArray(_Symbol$iterator3, 0);
+var _Symbol$iterator5 = {
+    [Symbol.iterator]: () => () => {}
+  },
+  _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$iterator9 = {
+    [Symbol.iterator]: () => {
+      return {
+        return: () => {
+          returnCalled = true;
+          return {};
+        }
+      };
+    }
+  },
+  _Symbol$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-plugin-transform-destructuring/test/fixtures/destructuring/next-eval-once/exec.js

@@ -0,0 +1,22 @@
+let gets = 0;
+let it = {
+  [Symbol.iterator]: () => ({
+    get next() {
+      gets++;
+      let i = 0;
+      return () => ({ done: false, value: i++ });
+    },
+  }),
+};
+
+let [] = it;
+expect(gets).toBe(1);
+
+let [a] = it;
+expect(gets).toBe(2);
+expect(a).toBe(0);
+
+let [b, c] = it;
+expect(gets).toBe(3);
+expect(b).toBe(0);
+expect(c).toBe(1);

packages/babel-plugin-transform-destructuring/test/fixtures/regression/15154/exec.js

@@ -0,0 +1,3 @@
+expect(() => {
+  var [] = { [Symbol.iterator]: () => [] };
+}).not.toThrow();

packages/babel-plugin-transform-destructuring/test/fixtures/regression/15154/input.js

@@ -0,0 +1 @@
+var [] = { [Symbol.iterator]: () => [] };

packages/babel-plugin-transform-destructuring/test/fixtures/regression/15154/options.json

@@ -0,0 +1,3 @@
+{
+  "plugins": ["transform-destructuring"]
+}

packages/babel-plugin-transform-destructuring/test/fixtures/regression/15154/output.js

@@ -0,0 +1,4 @@
+var _Symbol$iterator = {
+    [Symbol.iterator]: () => []
+  },
+  _Symbol$iterator2 = babelHelpers.slicedToArray(_Symbol$iterator, 0);

packages/babel-plugin-transform-destructuring/test/fixtures/regression/15168/exec.js

@@ -0,0 +1,3 @@
+expect(() => {
+  var [] = { [Symbol.iterator]: () => async function* () {} };
+}).not.toThrow();

packages/babel-plugin-transform-destructuring/test/fixtures/regression/15168/input.js

@@ -0,0 +1 @@
+var [] = { [Symbol.iterator]: () => async function* () {} };

packages/babel-plugin-transform-destructuring/test/fixtures/regression/15168/options.json

@@ -0,0 +1,6 @@
+{
+  "plugins": [
+    "transform-destructuring",
+    "transform-regenerator"
+  ]
+}

packages/babel-plugin-transform-destructuring/test/fixtures/regression/15168/output.js

@@ -0,0 +1,12 @@
+var _Symbol$iterator = {
+    [Symbol.iterator]: () => /*#__PURE__*/babelHelpers.regeneratorRuntime().mark(function _callee() {
+      return babelHelpers.regeneratorRuntime().async(function _callee$(_context) {
+        while (1) switch (_context.prev = _context.next) {
+          case 0:
+          case "end":
+            return _context.stop();
+        }
+      }, _callee, null, null, Promise);
+    })
+  },
+  _Symbol$iterator2 = babelHelpers.slicedToArray(_Symbol$iterator, 0);

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.