microsoft / microsoft/TypeScript
Intra expression inference doesn't work within reverse mapped types
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Descrizione
Bug Report
🔎 Search Terms
intra expression inference reverse mapped type
🕗 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)
💻 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(),
},
});
🙁 Actual behavior
This kind of inference that was improved in https://github.com/microsoft/TypeScript/pull/48538 doesn't work within a reverse mapped type.
🙂 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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Direzione di ricerca
Inizia con i due esempi Playground collegati, quindi esamina src/compiler/checker.ts in inferReverseMappedType e inferFromIntraExpressionSites, incluse le chiamate di inferenza citate e la gestione del contesto. Il lavoro è completo quando le funzioni non annotate produce e consume all’interno del reverse mapped type eseguono l’inferenza in modo coerente con gli esempi funzionanti e il codice riportato supera il controllo dei tipi.
Scritto dal modello di indicizzazione a partire dal testo della issue.
Valutazione
- Stack tecnologico
- typescript
- Ambito
- compilers
- Tipo di issue
- Bug
- Difficoltà
- 4/5
- Tempo stimato
- 3-5 giorni
- Stato di attività
- Ferma
- Chiarezza
- Abbastanza chiara
- Idoneità per principianti
- 38/100