Add additional tests for intra expression inference #48584
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The TypeScript team hasn't accepted the linked issue #45255. If you can get it accepted, this PR will have a better chance of being reviewed. |
| test({ | ||
| a: () => 0, | ||
| b: (a) => a, | ||
| c: (b) => { | ||
| const x: number = b; | ||
| } | ||
| }); |
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#45255 has 2 failing test cases, the 3rd call is basically the same as the call above this one here, but the 1st call (the one that is being added here) is slightly different - it "transfers" the return type from a to the c parameter type through the identity b. So it computes R1and R2 to be the same.
Perhaps it's not that different from the other test case but maybe it's worth adding - i will let you be the judge of that 😉
| declare const branch: | ||
| <T, U extends T>(_: { test: T, if: (t: T) => t is U, then: (u: U) => void }) => void | ||
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| declare const x: "a" | "b" | ||
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| branch({ | ||
| test: x, | ||
| if: (t): t is "a" => t === "a", | ||
| then: u => { | ||
| let test1: "a" = u | ||
| } | ||
| }) |
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This is very similar to some other cases here but this has an interesting return type annotation at if. Previously u in then was inferred to be of type 'a' | 'b' but now it gets correctly narrowed down to 'a'
related to #48538
closes #45255