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Await nullish async disposable #16408

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merged 5 commits into from
Apr 4, 2024

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JLHwung
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@JLHwung JLHwung commented Apr 3, 2024

Q                       A
Fixed Issues? When an async-disposable is nullish, Babel does not await its disposing process (REPL)
Patch: Bug Fix? Yes
Major: Breaking Change?
Minor: New Feature?
Tests Added + Pass? Yes
Documentation PR Link
Any Dependency Changes?
License MIT

In the REPL example,

(async function () {
  const log = [];

  function disposable(name) {
    return {
      async [Symbol.dispose || Symbol.for("Symbol.dispose")]() {
        log.push(name);
      },
    };
  }

  async function f() {
    using y = disposable("y");
    await using x = null;
    log.push("f body");
  }

  const promise = f();

  log.push("body");

  await promise;

  console.log(log)
})()

It should log "f body", "body", "y", but currently it logs "f body", "y", "body".

Per spec 7.5.7 Dispose, if hint is async-dispose, the result should be awaited, even if it is nullish. Therefore the disposing of the next resource y should follow log.push("body").

@JLHwung JLHwung added PR: Bug Fix 🐛 A type of pull request used for our changelog categories Spec: Explicit Resource Management labels Apr 3, 2024
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babel-bot commented Apr 3, 2024

Build successful! You can test your changes in the REPL here: https://babeljs.io/repl/build/56669

@@ -39,6 +39,8 @@ export default function _usingCtx() {
throw new TypeError(`Property [Symbol.dispose] is not a function.`);
}
stack.push({ v: value, d: dispose, a: isAwait });
} else if (isAwait) {
stack.push({ a: isAwait });
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Can you explicitly set d to undefined, given that we read it later?

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Or set it to false to save a few bytes?

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@liuxingbaoyu liuxingbaoyu Apr 4, 2024

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We could probably use value here.

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Anything works for me as long as it's something :)

@JLHwung JLHwung force-pushed the await-nullish-async-disposable branch from 6ef1fe9 to 6600aec Compare April 4, 2024 14:15
@@ -39,6 +39,9 @@ export default function _usingCtx() {
throw new TypeError(`Property [Symbol.dispose] is not a function.`);
}
stack.push({ v: value, d: dispose, a: isAwait });
} else if (isAwait) {
// provide the nullish `value` as `d` for minification gain
stack.push({ d: value, a: isAwait });
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Aside: currently await using x = document.all will go to this branch, we probably should reject it. I will check the spec and open a new PR to fix that.

@JLHwung JLHwung merged commit 3e96f03 into babel:main Apr 4, 2024
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@JLHwung JLHwung deleted the await-nullish-async-disposable branch April 4, 2024 14:37
@nicolo-ribaudo
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There will be some changes related to this in the proposal: tc39/proposal-explicit-resource-management#219

We will have a conclusion at the end of the week.

@github-actions github-actions bot added the outdated A closed issue/PR that is archived due to age. Recommended to make a new issue label Jul 10, 2024
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4 participants