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Improve output of for await #15943

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fcad16f
improve
liuxingbaoyu Sep 8, 2023
4b22260
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liuxingbaoyu Sep 9, 2023
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liuxingbaoyu Sep 10, 2023
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50 changes: 16 additions & 34 deletions packages/babel-plugin-transform-async-generator-functions/src/for-await.ts
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Original file line number Diff line number Diff line change
@@ -1,31 +1,21 @@
import { types as t, template } from "@babel/core";
import type { NodePath } from "@babel/traverse";

const buildForAwait = template(`
async function wrapper() {
var ITERATOR_ABRUPT_COMPLETION = false;
var ITERATOR_HAD_ERROR_KEY = false;
var ITERATOR_ERROR_KEY;
const buildForAwait = template.statements(`
var ITERATOR_KEY = GET_ITERATOR(OBJECT), STEP_KEY = {}, NOT_DONE_KEY;
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Is there an upside to initializing STEP_KEY here? It'll be overwritten before use.

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Now it's no longer needed, thank you!

try {
for (;NOT_DONE_KEY = !(STEP_KEY = await ITERATOR_KEY.next()).done;NOT_DONE_KEY = false) {
}
} catch(e) {
STEP_KEY = null;
throw e;
} finally {
try {
for (
var ITERATOR_KEY = GET_ITERATOR(OBJECT), STEP_KEY;
ITERATOR_ABRUPT_COMPLETION = !(STEP_KEY = await ITERATOR_KEY.next()).done;
ITERATOR_ABRUPT_COMPLETION = false
) {
}
} catch (err) {
ITERATOR_HAD_ERROR_KEY = true;
ITERATOR_ERROR_KEY = err;
} finally {
try {
if (ITERATOR_ABRUPT_COMPLETION && ITERATOR_KEY.return != null) {
await ITERATOR_KEY.return();
}
} finally {
if (ITERATOR_HAD_ERROR_KEY) {
throw ITERATOR_ERROR_KEY;
}
if (NOT_DONE_KEY && ITERATOR_KEY.return) {
await ITERATOR_KEY.return();
}
} catch (e) {
if (STEP_KEY) throw e;
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Suggested change
if (STEP_KEY) throw e;
if (STEP_KEY != null) throw e;

.next() might set Boolean.prototype.done to true and return false :)

Could you also rename _notDone to _iteratorAbruptCompletion, to reduce the diff and make it easier to follow the changes?

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nit: .next() must return an Object; otherwise agree explicit null-check looks clearer.

ForIn/OfBodyEvaluation

6.c. If nextResult is not an Object, throw a TypeError exception.

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.next() might set Boolean.prototype.done to true and return false :)

I'm not sure if it's worth doing, it's really weird usage. :)

Could you also rename _notDone to _iteratorAbruptCompletion, to reduce the diff and make it easier to follow the changes?

Since I completely changed the position of variable declarations and the logic of throwing exceptions, the changes may not be less, _notDone is slightly shorter and easier to read in the output.

}
}
`);
Expand All @@ -52,24 +42,16 @@ export default function (
t.variableDeclarator(left.declarations[0].id, stepValue),
]);
}
let template = buildForAwait({
ITERATOR_HAD_ERROR_KEY: scope.generateUidIdentifier("didIteratorError"),
ITERATOR_ABRUPT_COMPLETION: scope.generateUidIdentifier(
"iteratorAbruptCompletion",
),
ITERATOR_ERROR_KEY: scope.generateUidIdentifier("iteratorError"),
const template = buildForAwait({
ITERATOR_KEY: scope.generateUidIdentifier("iterator"),
NOT_DONE_KEY: scope.generateUidIdentifier("notDone"),
GET_ITERATOR: getAsyncIterator,
OBJECT: node.right,
STEP_KEY: t.cloneNode(stepKey),
});

// remove async function wrapper
// @ts-expect-error todo(flow->ts) improve type annotation for buildForAwait
template = template.body.body as t.Statement[];

const isLabeledParent = t.isLabeledStatement(parent);
const tryBody = (template[3] as t.TryStatement).block.body;
const tryBody = (template[1] as t.TryStatement).block.body;
const loop = tryBody[0] as t.ForStatement;

if (isLabeledParent) {
Expand Down
22 changes: 10 additions & 12 deletions ...-plugin-transform-async-generator-functions/test/fixtures/for-await/async-arrow/output.js
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Original file line number Diff line number Diff line change
@@ -1,26 +1,24 @@
/*#__PURE__*/babelHelpers.asyncToGenerator(function* () {
var _iteratorAbruptCompletion = false;
var _didIteratorError = false;
var _iteratorError;
var _iterator = babelHelpers.asyncIterator(y),
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If calling y[Symbol.asyncIterator]() throws, does this still behave the same?

_step = {},
_notDone;
try {
for (var _iterator = babelHelpers.asyncIterator(y), _step; _iteratorAbruptCompletion = !(_step = yield _iterator.next()).done; _iteratorAbruptCompletion = false) {
for (; _notDone = !(_step = yield _iterator.next()).done; _notDone = false) {
let x = _step.value;
{
f(x);
}
}
} catch (err) {
_didIteratorError = true;
_iteratorError = err;
} catch (e) {
_step = null;
throw e;
} finally {
try {
if (_iteratorAbruptCompletion && _iterator.return != null) {
if (_notDone && _iterator.return) {
yield _iterator.return();
}
} finally {
if (_didIteratorError) {
throw _iteratorError;
}
} catch (e) {
if (_step) throw e;
}
}
});
22 changes: 10 additions & 12 deletions ...m-async-generator-functions/test/fixtures/for-await/async-function-no-transform/output.js
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Original file line number Diff line number Diff line change
@@ -1,23 +1,21 @@
async function foo() {
var _iteratorAbruptCompletion = false;
var _didIteratorError = false;
var _iteratorError;
var _iterator = babelHelpers.asyncIterator(y),
_step = {},
_notDone;
try {
for (var _iterator = babelHelpers.asyncIterator(y), _step; _iteratorAbruptCompletion = !(_step = await _iterator.next()).done; _iteratorAbruptCompletion = false) {
for (; _notDone = !(_step = await _iterator.next()).done; _notDone = false) {
const x = _step.value;
}
} catch (err) {
_didIteratorError = true;
_iteratorError = err;
} catch (e) {
_step = null;
throw e;
} finally {
try {
if (_iteratorAbruptCompletion && _iterator.return != null) {
if (_notDone && _iterator.return) {
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If _iterator.return is falsy but not nullish, we should still call it to get the proper TypeError.

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Only undefined should skip the call.

await _iterator.return();
}
} finally {
if (_didIteratorError) {
throw _iteratorError;
}
} catch (e) {
if (_step) throw e;
}
}
}
22 changes: 10 additions & 12 deletions ...ugin-transform-async-generator-functions/test/fixtures/for-await/async-function/output.js
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Original file line number Diff line number Diff line change
@@ -1,28 +1,26 @@
var _f;
function f() {
return (_f = _f || babelHelpers.asyncToGenerator(function* () {
var _iteratorAbruptCompletion = false;
var _didIteratorError = false;
var _iteratorError;
var _iterator = babelHelpers.asyncIterator(y),
_step = {},
_notDone;
try {
for (var _iterator = babelHelpers.asyncIterator(y), _step; _iteratorAbruptCompletion = !(_step = yield _iterator.next()).done; _iteratorAbruptCompletion = false) {
for (; _notDone = !(_step = yield _iterator.next()).done; _notDone = false) {
let x = _step.value;
{
g(x);
}
}
} catch (err) {
_didIteratorError = true;
_iteratorError = err;
} catch (e) {
_step = null;
throw e;
} finally {
try {
if (_iteratorAbruptCompletion && _iterator.return != null) {
if (_notDone && _iterator.return) {
yield _iterator.return();
}
} finally {
if (_didIteratorError) {
throw _iteratorError;
}
} catch (e) {
if (_step) throw e;
}
}
})).apply(this, arguments);
Expand Down
22 changes: 10 additions & 12 deletions ...gin-transform-async-generator-functions/test/fixtures/for-await/async-generator/output.js
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Original file line number Diff line number Diff line change
@@ -1,28 +1,26 @@
var _g;
function g() {
return (_g = _g || babelHelpers.wrapAsyncGenerator(function* () {
var _iteratorAbruptCompletion = false;
var _didIteratorError = false;
var _iteratorError;
var _iterator = babelHelpers.asyncIterator(y),
_step = {},
_notDone;
try {
for (var _iterator = babelHelpers.asyncIterator(y), _step; _iteratorAbruptCompletion = !(_step = yield babelHelpers.awaitAsyncGenerator(_iterator.next())).done; _iteratorAbruptCompletion = false) {
for (; _notDone = !(_step = yield babelHelpers.awaitAsyncGenerator(_iterator.next())).done; _notDone = false) {
let x = _step.value;
{
f(x);
}
}
} catch (err) {
_didIteratorError = true;
_iteratorError = err;
} catch (e) {
_step = null;
throw e;
} finally {
try {
if (_iteratorAbruptCompletion && _iterator.return != null) {
if (_notDone && _iterator.return) {
yield babelHelpers.awaitAsyncGenerator(_iterator.return());
}
} finally {
if (_didIteratorError) {
throw _iteratorError;
}
} catch (e) {
if (_step) throw e;
}
}
})).apply(this, arguments);
Expand Down
22 changes: 10 additions & 12 deletions ...ync-generator-functions/test/fixtures/for-await/create-async-from-sync-iterator/output.js
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Original file line number Diff line number Diff line change
@@ -1,30 +1,28 @@
var _fn;
function fn() {
return (_fn = _fn || babelHelpers.wrapAsyncGenerator(function* () {
var _iteratorAbruptCompletion = false;
var _didIteratorError = false;
var _iteratorError;
var _iterator = babelHelpers.asyncIterator([Promise.resolve("ok")]),
_step = {},
_notDone;
try {
for (var _iterator = babelHelpers.asyncIterator([Promise.resolve("ok")]), _step; _iteratorAbruptCompletion = !(_step = yield babelHelpers.awaitAsyncGenerator(_iterator.next())).done; _iteratorAbruptCompletion = false) {
for (; _notDone = !(_step = yield babelHelpers.awaitAsyncGenerator(_iterator.next())).done; _notDone = false) {
const result = _step.value;
{
return {
result
};
}
}
} catch (err) {
_didIteratorError = true;
_iteratorError = err;
} catch (e) {
_step = null;
throw e;
} finally {
try {
if (_iteratorAbruptCompletion && _iterator.return != null) {
if (_notDone && _iterator.return) {
yield babelHelpers.awaitAsyncGenerator(_iterator.return());
}
} finally {
if (_didIteratorError) {
throw _iteratorError;
}
} catch (e) {
if (_step) throw e;
}
}
})).apply(this, arguments);
Expand Down
22 changes: 10 additions & 12 deletions ...lugin-transform-async-generator-functions/test/fixtures/for-await/destructuring/output.js
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Original file line number Diff line number Diff line change
@@ -1,11 +1,11 @@
var _f;
function f() {
return (_f = _f || babelHelpers.asyncToGenerator(function* () {
var _iteratorAbruptCompletion = false;
var _didIteratorError = false;
var _iteratorError;
var _iterator = babelHelpers.asyncIterator(a),
_step = {},
_notDone;
try {
for (var _iterator = babelHelpers.asyncIterator(a), _step; _iteratorAbruptCompletion = !(_step = yield _iterator.next()).done; _iteratorAbruptCompletion = false) {
for (; _notDone = !(_step = yield _iterator.next()).done; _notDone = false) {
let {
x,
y: [z]
Expand All @@ -14,18 +14,16 @@ function f() {
g(x, z);
}
}
} catch (err) {
_didIteratorError = true;
_iteratorError = err;
} catch (e) {
_step = null;
throw e;
} finally {
try {
if (_iteratorAbruptCompletion && _iterator.return != null) {
if (_notDone && _iterator.return) {
yield _iterator.return();
}
} finally {
if (_didIteratorError) {
throw _iteratorError;
}
} catch (e) {
if (_step) throw e;
}
}
})).apply(this, arguments);
Expand Down
22 changes: 10 additions & 12 deletions ...ansform-async-generator-functions/test/fixtures/for-await/lhs-member-expression/output.js
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Original file line number Diff line number Diff line change
@@ -1,23 +1,21 @@
babelHelpers.asyncToGenerator(function* () {
var _iteratorAbruptCompletion = false;
var _didIteratorError = false;
var _iteratorError;
var _iterator = babelHelpers.asyncIterator(y),
_step = {},
_notDone;
try {
for (var _iterator = babelHelpers.asyncIterator(y), _step; _iteratorAbruptCompletion = !(_step = yield _iterator.next()).done; _iteratorAbruptCompletion = false) {
for (; _notDone = !(_step = yield _iterator.next()).done; _notDone = false) {
obj.x = _step.value;
}
} catch (err) {
_didIteratorError = true;
_iteratorError = err;
} catch (e) {
_step = null;
throw e;
} finally {
try {
if (_iteratorAbruptCompletion && _iterator.return != null) {
if (_notDone && _iterator.return) {
yield _iterator.return();
}
} finally {
if (_didIteratorError) {
throw _iteratorError;
}
} catch (e) {
if (_step) throw e;
}
}
})();
22 changes: 10 additions & 12 deletions ...m-async-generator-functions/test/fixtures/for-await/re-declare-var-in-init-body/output.js
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Original file line number Diff line number Diff line change
@@ -1,26 +1,24 @@
/*#__PURE__*/babelHelpers.asyncToGenerator(function* () {
var _iteratorAbruptCompletion = false;
var _didIteratorError = false;
var _iteratorError;
var _iterator = babelHelpers.asyncIterator([]),
_step = {},
_notDone;
try {
for (var _iterator = babelHelpers.asyncIterator([]), _step; _iteratorAbruptCompletion = !(_step = yield _iterator.next()).done; _iteratorAbruptCompletion = false) {
for (; _notDone = !(_step = yield _iterator.next()).done; _notDone = false) {
let x = _step.value;
{
let x;
}
}
} catch (err) {
_didIteratorError = true;
_iteratorError = err;
} catch (e) {
_step = null;
throw e;
} finally {
try {
if (_iteratorAbruptCompletion && _iterator.return != null) {
if (_notDone && _iterator.return) {
yield _iterator.return();
}
} finally {
if (_didIteratorError) {
throw _iteratorError;
}
} catch (e) {
if (_step) throw e;
}
}
});