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Intra expression inference doesn't work within reverse mapped typesΒ #53018

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@Andarist

Description

@Andarist

Bug Report

πŸ”Ž Search Terms

intra expression inference reverse mapped type

πŸ•— Version & Regression Information

  • This is the behavior in every version I tried

⏯ Playground Link

Playground link with relevant code (object variant)
Playground link with relevant code (tuple variant)

πŸ’» Code

declare function f<T>(
  arg: {
    [K in keyof T]: {
      produce: (n: string) => T[K];
      consume: (x: T[K]) => void;
    };
  }
): void;
// Works
f({
  a: {
    produce: () => "hello",
    consume: (x) => x.toLowerCase(),
  },
});
// Works
f({
  a: {
    produce: (n: string) => n,
    consume: (x) => x.toLowerCase(),
  },
});
// still doesn't work, even with "Improved Function Inference in Objects and Methods" aka intra-expression inference sites
f({
  a: {
    produce: (n) => n,
    consume: (x) => x.toLowerCase(),
  },
});
// still doesn't work, even with "Improved Function Inference in Objects and Methods" aka intra-expression inference sites
f({
  a: {
    produce: function () {
      return "hello";
    },
    consume: (x) => x.toLowerCase(),
  },
});
// still doesn't work, even with "Improved Function Inference in Objects and Methods" aka intra-expression inference sites
f({
  a: {
    produce() {
      return "hello";
    },
    consume: (x) => x.toLowerCase(),
  },
});

πŸ™ Actual behavior

This kind of inference that was improved in #48538 doesn't work within a reverse mapped type.

πŸ™‚ Expected behavior

It should work in the same way as it does outside of the reverse mapped type. The code in the playground is almost literally taken from the 4.7 announcement blog post about this improvement (here). The only difference is that the produce/consume "pair" is within a property of reverse mapped type


Part of the problem is likely in that inferReverseMappedType calls inferTypes with separate inferences here:
https://github.dev/microsoft/TypeScript/blob/e2283e99b47942b863d016c65a3e430dca1549b9/src/compiler/checker.ts#L23938-L23939
and that is not linked anyhow to the current inference context and inferFromIntraExpressionSites tries to infer this kind of stuff from context.intraExpressionInferenceSites+context.inferences and the latter won't be present for the computed reverse mapped type inference:
https://github.dev/microsoft/TypeScript/blob/e2283e99b47942b863d016c65a3e430dca1549b9/src/compiler/checker.ts#L23756-L23763

However, I also noticed that inferReverseMappedType is not called at all in this case so those inferences for it aren't even gathered in the first place.

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