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Consider all constituents of contextual return type when resolving type of 'yield'#56222

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fix-42439
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Consider all constituents of contextual return type when resolving type of 'yield'#56222
rbuckton wants to merge 3 commits intomainfrom
fix-42439

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@rbuckton rbuckton commented Oct 25, 2023 •
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This avoids an early-exit in getIterationTypesOfIterable when the intended use is resolving the iteration types of a contextual return type of a generator function:

let f: () => Generator<string, void, string> | AsyncGenerator<string | void | string>;
f = function*() {
  let name: string;
  name = yield ""; 
};

The above code is an error currently as we drop the iteration types of the first constituent when the second fails.

For other uses we continue to preserve the early exit so that we correctly error for cases such as this:

let data: string[] | null;
const [value] = data; // should still be an error when the second constituent fails.

Fixes #42439

@typescript-bot typescript-bot added Author: Team For Milestone Bug PRs that fix a bug with a specific milestone labels Oct 25, 2023
Andarist added a commit to Andarist/TypeScript that referenced this pull request Oct 26, 2023
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Add test cases from microsoft#56222
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Andarist commented Oct 26, 2023

My old PR that awaits review already fixes this issue (I just pushed out a test case that is being added here in this PR). It also shares all of the baseline changes that you have here.

Would you mind re-reviewing that PR and comparing the used approaches? Maybe it would be also good to pull all the other test cases that I added there here to compare their results?

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rbuckton commented Oct 26, 2023

My old PR that awaits review already fixes this issue (I just pushed out a test case that is being added here in this PR). It also shares all of the baseline changes that you have here.

Would you mind re-reviewing that PR and comparing the used approaches? Maybe it would be also good to pull all the other test cases that I added there here to compare their results?

The test in tests/cases/compiler/contextuallyTypeAsyncFunctionReturnTypeFromUnion.ts fails in my branch. It looks like your PR covers more cases, so I'll happily close this branch in favor of your PR.

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rbuckton commented Oct 26, 2023

Closed in favor of #51196.

@rbuckton rbuckton closed this Oct 26, 2023
@rbuckton rbuckton deleted the fix-42439 branch October 26, 2023 15:25
@microsoft microsoft locked as resolved and limited conversation to collaborators Oct 22, 2025
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Union of Generator and AsyncGenerator introduces spurious undefined next() value path

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