feat(eslint-plugin): [await-thenable] check for-await loop iteree #10008
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| ## Async Iteration (`for await...of` Loops) | ||
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| This rule also inspects [`for await...of` statements](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/for-await...of), which are designed for iterating over async-iterable objects. | ||
| If the value being iterated over is not async-iterable, an ordinary `for...of` statement is preferable, even if the value is an iterable of Thenables. |
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This is debatable. Banning iterables of thenables should be an option.
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Eh, kind of... in any case, I was going off of #8858 (comment). It's easy enough to add an option to allow iterables of thenables, though I'm -0.5 on doing so.
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In lieu of an option, can we add more motivation to the docs (as what I said in that comment)?
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Good point! Made some changes around this 👍
Codecov ReportAll modified and coverable lines are covered by tests ✅
Additional details and impacted files@@ Coverage Diff @@
## main #10008 +/- ##
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+ Coverage 86.00% 86.03% +0.02%
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Files 425 428 +3
Lines 14810 14930 +120
Branches 4308 4329 +21
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+ Hits 12738 12845 +107
- Misses 1723 1741 +18
+ Partials 349 344 -5
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| // This suggestion causes broken code for sync iterables of promises, since | ||
| // the loop variable will not be awaited. | ||
| // | ||
| // Ideally, if the iterable yields promises, we would offer a suggestion to |
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bleh - I guess this isn't always a good idea, particularly with possibly infinite iterables. But, then again, why would you have an infinite sync iterable of promises? Thinking out loud.
| context.report({ | ||
| loc: getForStatementHeadLoc(context.sourceCode, node), | ||
| messageId: 'forAwaitOfNonThenable', | ||
| suggest: [ |
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Can we only offer this suggestion if the iterator result is not thenable?
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I don't think so because we'd need getIterationTypesOfIterable() or getIteratedTypeOrElementType or similar from TS none of which is exposed on the checker.
If we check arrays and tuples specifically, i.e. known iterables, this is silly since
for (const promisedValue of await Promise.all(promises)) {
}is a much better suggestion in those cases (since awaiting in the loop is generally problematic for exception handling given a non-lazy array of promises)
Whereas with lazy sync-iterables of promises, which I don't know if we can detect, it may be better to do
for (const promise of yieldPromises()) {
const promisedValue = await promise;
}I guess the only thing that's unambiguous here is that if you have an array or tuple of non-thenables, this suggestion is good. Maybe that's the only situation where we give a suggestion?
Co-authored-by: Joshua Chen <[email protected]>
Co-authored-by: Joshua Chen <[email protected]>
b121bd9
into
typescript-eslint:main
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wrong rule in title lol |
smh 😞. Changing the title and release notes, thanks for pointing this out! |
PR Checklist
for-awaitloop is used on an async iterable #8858Overview
Just ask the type checker if a
Symbol.asyncIteratoris present, ezpz. Add tests and docs (less ezpz).