Function sent (#5920)

* Create "babel-helper-wrap-function"

It contains the logic to wrap a function inside a call expression.
It was part of the "babel-helper-remap-async-to-generator" package, but
it is needed to transpile "function.sent"

* Create "babel-transform-function-sent"

It transforms the "function.sent" meta property by replacing it with
"yield" and making the generator ignore the first ".next()" call.

* "function.sent" is the last value passed to .next(), not the first one

* Disable exec tests on old node

* Fix flow error

* Add "transform-function-sent" to "stage-2" preset

* Do every trasformation in one traversal

* Test for "yield function.sent"

* [skip ci]

* Fix some typos [skip ci]

packages/babel-plugin-transform-function-sent/.npmignore

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+src
+test
+*.log

packages/babel-plugin-transform-function-sent/README.md

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+# babel-plugin-transform-function-sent
+
+> Compile the `function.sent` meta property, used inside generator functions, to valid ES2015 code.
+
+## Example
+
+```js
+function* generator() {
+    console.log("Sent", function.sent);
+    console.log("Yield", yield);
+}
+
+const iterator = generator();
+iterator.next(1); // Logs "Sent 1"
+iterator.next(2); // Logs "Yield 2"
+```
+
+Is compiled roughly to
+
+```js
+let generator = _skipFirstGeneratorNext(function* () {
+    const _functionSent = yield;
+    console.log("Sent", _functionSent);
+    console.log("Yield", yield);
+});
+
+const iterator = generator();
+iterator.next(1); // Logs "Sent 1"
+iterator.next(2); // Logs "Yield 1"
+```
+
+## Installation
+
+```sh
+npm install --save-dev babel-plugin-transform-function-sent
+```
+
+## Usage
+
+### Via `.babelrc` (Recommended)
+
+**.babelrc**
+
+```json
+{
+  "plugins": ["transform-function-sent"]
+}
+```
+
+### Via CLI
+
+```sh
+babel --plugins transform-function-sent script.js
+```
+
+### Via Node API
+
+```javascript
+require("babel-core").transform("code", {
+  plugins: ["transform-function-sent"]
+});
+```
+
+## References
+
+* [Proposal](https://github.com/allenwb/ESideas/blob/master/Generator%20metaproperty.md)

packages/babel-plugin-transform-function-sent/package.json

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+{
+  "name": "babel-plugin-transform-function-sent",
+  "version": "7.0.0-alpha.15",
+  "description": "Compile the function.sent meta propety to valid ES2015 code",
+  "repository": "https://github.com/babel/babel/tree/master/packages/babel-plugin-transform-function-sent",
+  "license": "MIT",
+  "main": "lib/index.js",
+  "keywords": [
+    "babel-plugin"
+  ],
+  "dependencies": {
+    "babel-plugin-syntax-function-sent": "7.0.0-alpha.15",
+    "babel-helper-wrap-function": "7.0.0-alpha.15"
+  },
+  "devDependencies": {
+    "babel-helper-plugin-test-runner": "7.0.0-alpha.15"
+  }
+}

packages/babel-plugin-transform-function-sent/src/index.js

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+import syntaxFunctionSent from "babel-plugin-syntax-function-sent";
+import wrapFunction from "babel-helper-wrap-function";
+
+export default function({ types: t }) {
+  const isFunctionSent = node =>
+    t.isIdentifier(node.meta, { name: "function" }) &&
+    t.isIdentifier(node.property, { name: "sent" });
+
+  const yieldVisitor = {
+    Function(path) {
+      path.skip();
+    },
+
+    YieldExpression(path) {
+      const replaced = t.isAssignmentExpression(path.parent, {
+        left: this.sentId,
+      });
+      if (!replaced) {
+        path.replaceWith(t.assignmentExpression("=", this.sentId, path.node));
+      }
+    },
+
+    MetaProperty(path) {
+      if (isFunctionSent(path.node)) {
+        path.replaceWith(this.sentId);
+      }
+    },
+  };
+
+  return {
+    inherits: syntaxFunctionSent,
+
+    visitor: {
+      MetaProperty(path, state) {
+        if (!isFunctionSent(path.node)) return;
+
+        const fnPath = path.getFunctionParent();
+
+        if (!fnPath.node.generator) {
+          throw new Error("Parent generator function not found");
+        }
+
+        const sentId = path.scope.generateUidIdentifier("function.sent");
+
+        fnPath.traverse(yieldVisitor, { sentId });
+        fnPath.node.body.body.unshift(
+          t.variableDeclaration("let", [
+            t.variableDeclarator(sentId, t.yieldExpression()),
+          ]),
+        );
+
+        wrapFunction(fnPath, state.addHelper("skipFirstGeneratorNext"));
+      },
+    },
+  };
+}

packages/babel-plugin-transform-function-sent/test/fixtures/function-sent/basic/actual.js

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+function* gen() {
+    let sent = function.sent;
+}

packages/babel-plugin-transform-function-sent/test/fixtures/function-sent/basic/exec.js

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+let sent, yielded;
+
+function* gen() {
+    sent = function.sent;
+    yielded = yield;
+}
+
+const it = gen();
+it.next(1);
+it.next(2);
+
+assert.equal(sent, 1);
+assert.equal(yielded, 2);

packages/babel-plugin-transform-function-sent/test/fixtures/function-sent/basic/expected.js

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+let gen = (() => {
+  var _ref = _skipFirstGeneratorNext(function* () {
+    let _functionSent = yield;
+
+    let sent = _functionSent;
+  });
+
+  return function gen() {
+    return _ref.apply(this, arguments);
+  };
+})();
+
+function _skipFirstGeneratorNext(fn) { return function () { var it = fn.apply(this, arguments); it.next(); return it; }; }

packages/babel-plugin-transform-function-sent/test/fixtures/function-sent/basic/options.json

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+{
+  "minNodeVersion": "6.0.0"
+}

packages/babel-plugin-transform-function-sent/test/fixtures/function-sent/multiple/actual.js

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+(function* () {
+  const a = function.sent;
+  const b = function.sent;
+  yield 4;
+  const c = function.sent;
+  const d = yield;
+  const e = function.sent;
+
+  return [ a, b, c, d, e ];
+}());

packages/babel-plugin-transform-function-sent/test/fixtures/function-sent/multiple/exec.js

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+const values = [];
+
+function* gen() {
+  values.push(function.sent);
+  values.push(function.sent);
+  values.push(yield "foo");
+  values.push(function.sent);
+  values.push(yield);
+  values.push(function.sent);
+  values.push(function.sent);
+}
+
+const it = gen();
+assert.deepEqual(values, []);
+
+assert.equal(it.next(1).value, "foo");
+assert.deepEqual(values, [ 1, 1 ]);
+
+assert.equal(it.next(2).value, undefined);
+assert.deepEqual(values, [ 1, 1, 2, 2 ]);
+
+assert.equal(it.next(3).done, true);
+assert.deepEqual(values, [ 1, 1, 2, 2, 3, 3, 3 ]);

packages/babel-plugin-transform-function-sent/test/fixtures/function-sent/multiple/expected.js

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+function _skipFirstGeneratorNext(fn) { return function () { var it = fn.apply(this, arguments); it.next(); return it; }; }
+
+_skipFirstGeneratorNext(function* () {
+  let _functionSent = yield;
+
+  const a = _functionSent;
+  const b = _functionSent;
+  _functionSent = yield 4;
+  const c = _functionSent;
+  const d = _functionSent = yield;
+  const e = _functionSent;
+  return [a, b, c, d, e];
+})();

packages/babel-plugin-transform-function-sent/test/fixtures/function-sent/multiple/options.json

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+{
+  "minNodeVersion": "6.0.0"
+}

packages/babel-plugin-transform-function-sent/test/fixtures/function-sent/options.json

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+{
+  "plugins": ["transform-function-sent"]
+}

packages/babel-plugin-transform-function-sent/test/fixtures/function-sent/without-function-sent/actual.js

@@ -0,0 +1,4 @@
+function* foo() {
+  let a = yield;
+  return yield;
+}

packages/babel-plugin-transform-function-sent/test/fixtures/function-sent/without-function-sent/expected.js

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+function* foo() {
+  let a = yield;
+  return yield;
+}

packages/babel-plugin-transform-function-sent/test/fixtures/function-sent/yield-function-sent/actual.js

@@ -0,0 +1,3 @@
+(function* () {
+  yield function.sent;
+})();

packages/babel-plugin-transform-function-sent/test/fixtures/function-sent/yield-function-sent/expected.js

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+function _skipFirstGeneratorNext(fn) { return function () { var it = fn.apply(this, arguments); it.next(); return it; }; }
+
+_skipFirstGeneratorNext(function* () {
+  let _functionSent = yield;
+
+  _functionSent = yield _functionSent;
+})();

packages/babel-plugin-transform-function-sent/test/fixtures/generator-kinds/async-generator/actual.js

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+async function* foo() {
+  await function.sent;
+}

packages/babel-plugin-transform-function-sent/test/fixtures/generator-kinds/async-generator/expected.js

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+var _asyncGenerator = function () { function AwaitValue(value) { this.value = value; } function AsyncGenerator(gen) { var front, back; function send(key, arg) { return new Promise(function (resolve, reject) { var request = { key: key, arg: arg, resolve: resolve, reject: reject, next: null }; if (back) { back = back.next = request; } else { front = back = request; resume(key, arg); } }); } function resume(key, arg) { try { var result = gen[key](arg); var value = result.value; if (value instanceof AwaitValue) { Promise.resolve(value.value).then(function (arg) { resume("next", arg); }, function (arg) { resume("throw", arg); }); } else { settle(result.done ? "return" : "normal", result.value); } } catch (err) { settle("throw", err); } } function settle(type, value) { switch (type) { case "return": front.resolve({ value: value, done: true }); break; case "throw": front.reject(value); break; default: front.resolve({ value: value, done: false }); break; } front = front.next; if (front) { resume(front.key, front.arg); } else { back = null; } } this._invoke = send; if (typeof gen.return !== "function") { this.return = undefined; } } if (typeof Symbol === "function" && Symbol.asyncIterator) { AsyncGenerator.prototype[Symbol.asyncIterator] = function () { return this; }; } AsyncGenerator.prototype.next = function (arg) { return this._invoke("next", arg); }; AsyncGenerator.prototype.throw = function (arg) { return this._invoke("throw", arg); }; AsyncGenerator.prototype.return = function (arg) { return this._invoke("return", arg); }; return { wrap: function (fn) { return function () { return new AsyncGenerator(fn.apply(this, arguments)); }; }, await: function (value) { return new AwaitValue(value); } }; }();
+
+let foo = (() => {
+  var _ref = _asyncGenerator.wrap(_skipFirstGeneratorNext(function* () {
+    let _functionSent = yield;
+
+    _functionSent = yield _asyncGenerator.await(_functionSent);
+  }));
+
+  return function foo() {
+    return _ref.apply(this, arguments);
+  };
+})();
+
+function _skipFirstGeneratorNext(fn) { return function () { var it = fn.apply(this, arguments); it.next(); return it; }; }

packages/babel-plugin-transform-function-sent/test/fixtures/generator-kinds/async-generator/options.json

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+{
+  "plugins": [ "transform-function-sent", "transform-async-generator-functions" ]
+}

packages/babel-plugin-transform-function-sent/test/fixtures/generator-kinds/class-method/actual.js

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+class Foo {
+  *gen() {
+    return function.sent;
+  }
+}

packages/babel-plugin-transform-function-sent/test/fixtures/generator-kinds/class-method/expected.js

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+function _skipFirstGeneratorNext(fn) { return function () { var it = fn.apply(this, arguments); it.next(); return it; }; }
+
+class Foo {
+  gen() {
+    return _skipFirstGeneratorNext(function* () {
+      let _functionSent = yield;
+
+      return _functionSent;
+    })();
+  }
+
+}

packages/babel-plugin-transform-function-sent/test/fixtures/generator-kinds/export-default-anonymous/actual.js

@@ -0,0 +1,3 @@
+export default function* () {
+  return function.sent;
+}

packages/babel-plugin-transform-function-sent/test/fixtures/generator-kinds/export-default-anonymous/expected.js

@@ -0,0 +1,7 @@
+function _skipFirstGeneratorNext(fn) { return function () { var it = fn.apply(this, arguments); it.next(); return it; }; }
+
+export default _skipFirstGeneratorNext(function* () {
+  let _functionSent = yield;
+
+  return _functionSent;
+});

packages/babel-plugin-transform-function-sent/test/fixtures/generator-kinds/export-default-named/actual.js

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+export default function* gen() {
+  return function.sent;
+}

packages/babel-plugin-transform-function-sent/test/fixtures/generator-kinds/export-default-named/expected.js

@@ -0,0 +1,15 @@
+let gen = (() => {
+  var _ref = _skipFirstGeneratorNext(function* () {
+    let _functionSent = yield;
+
+    return _functionSent;
+  });
+
+  return function gen() {
+    return _ref.apply(this, arguments);
+  };
+})();
+
+function _skipFirstGeneratorNext(fn) { return function () { var it = fn.apply(this, arguments); it.next(); return it; }; }
+
+export { gen as default };

packages/babel-plugin-transform-function-sent/test/fixtures/generator-kinds/export/actual.js

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+export function* gen() {
+  return function.sent;
+}

packages/babel-plugin-transform-function-sent/test/fixtures/generator-kinds/export/expected.js

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+function _skipFirstGeneratorNext(fn) { return function () { var it = fn.apply(this, arguments); it.next(); return it; }; }
+
+export let gen = (() => {
+  var _ref = _skipFirstGeneratorNext(function* () {
+    let _functionSent = yield;
+
+    return _functionSent;
+  });
+
+  return function gen() {
+    return _ref.apply(this, arguments);
+  };
+})();

packages/babel-plugin-transform-function-sent/test/fixtures/generator-kinds/expression-anonymous/actual.js

@@ -0,0 +1,3 @@
+(function* () {
+  return function.sent;
+}());

packages/babel-plugin-transform-function-sent/test/fixtures/generator-kinds/expression-anonymous/expected.js

@@ -0,0 +1,7 @@
+function _skipFirstGeneratorNext(fn) { return function () { var it = fn.apply(this, arguments); it.next(); return it; }; }
+
+_skipFirstGeneratorNext(function* () {
+  let _functionSent = yield;
+
+  return _functionSent;
+})();

packages/babel-plugin-transform-function-sent/test/fixtures/generator-kinds/expression-named/actual.js

@@ -0,0 +1,3 @@
+const foo = function* gen() {
+  return function.sent;
+};

packages/babel-plugin-transform-function-sent/test/fixtures/generator-kinds/expression-named/expected.js

@@ -0,0 +1,15 @@
+function _skipFirstGeneratorNext(fn) { return function () { var it = fn.apply(this, arguments); it.next(); return it; }; }
+
+const foo = (() => {
+  var _ref = _skipFirstGeneratorNext(function* () {
+    let _functionSent = yield;
+
+    return _functionSent;
+  });
+
+  function gen() {
+    return _ref.apply(this, arguments);
+  }
+
+  return gen;
+})();

packages/babel-plugin-transform-function-sent/test/fixtures/generator-kinds/object-method/actual.js

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+const obj = {
+  *gen() {
+    return function.sent;
+  },
+};

packages/babel-plugin-transform-function-sent/test/fixtures/generator-kinds/object-method/expected.js

@@ -0,0 +1,12 @@
+function _skipFirstGeneratorNext(fn) { return function () { var it = fn.apply(this, arguments); it.next(); return it; }; }
+
+const obj = {
+  gen() {
+    return _skipFirstGeneratorNext(function* () {
+      let _functionSent = yield;
+
+      return _functionSent;
+    })();
+  }
+
+};

packages/babel-plugin-transform-function-sent/test/fixtures/generator-kinds/options.json

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+{
+  "plugins": ["transform-function-sent"]
+}

packages/babel-plugin-transform-function-sent/test/fixtures/generator-kinds/statement/actual.js

@@ -0,0 +1,3 @@
+function* gen() {
+  return function.sent;
+}

packages/babel-plugin-transform-function-sent/test/fixtures/generator-kinds/statement/expected.js

@@ -0,0 +1,13 @@
+let gen = (() => {
+  var _ref = _skipFirstGeneratorNext(function* () {
+    let _functionSent = yield;
+
+    return _functionSent;
+  });
+
+  return function gen() {
+    return _ref.apply(this, arguments);
+  };
+})();
+
+function _skipFirstGeneratorNext(fn) { return function () { var it = fn.apply(this, arguments); it.next(); return it; }; }

packages/babel-plugin-transform-function-sent/test/index.js

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+import runner from "babel-helper-plugin-test-runner";
+
+runner(__dirname);