`silentNeverType` leak in contextual parameter types coming from anonymous non-aliased object type instantiations

🔎 Search Terms

silent never type return type inference alias propagating anonymous object

🕗 Version & Regression Information

• This is the behavior in every version I tried

⏯ Playground Link

https://www.typescriptlang.org/play/?ts=6.0.0-dev.20250827#code/JYOwLgpgTgZghgYwgAgAoB4AqA+ZBvAKGWTAAsIQAuZACgHsQYBXAGxmBZYgBNqaA3OCyYRqmAJTIAvLiYgA1iDoB3EJJnI5ilSADcBAL4ECoSLEQpUAYQYBnMFCYIwdKPiLIQEZcizYaEAAeEAhMLlB8UBC2dCz8orSCwgkS0rj8dMDc6umZ2dQYOPpGBNwhLHBRyIJuqAU2IPaOzq76peWVKMwgzsAMyDB0dACMfjSBfDlo6HjIZfCsYGLIBtjiYm0IdmDIUbaLw9IDQ8M0NFOExFFgTFAgnt5oZ3ux8RceV9GvEPrExAD0-2QAD0APweAziYpQ4xgACeAAcUAB1YBkAAiEAWLDAfiOs3mcEWywMbTKCAqVW6vX6gzoACYxhNaFMMKiMViiTi-GsNsYto0dntFvSjnT6Wd3p8bncHj5UM8vnEIFK-i9lb8-oCQeDiJDoWSOlS5DT7nSAMxMyZpaYAbUwAF1echMJttrtootzWKhubJTbLh6ZfcvPLFTFlarPhH4pqAUCwRCYfrjOTKV0TWA+mahgAWK0sm0YAmc4n4ZAIqB0BEklbO13893CnG5n10XP+jSB663EOPBU0dVvAMfD0xn6j7WJvXJmHtCmdAaZ7PHOgAVgL5yLMzmpZx1HtDrr6xdbsFY8Wa7ba87uG7EGDcqeg6Vw67o6HE7+yCnupWs90IA

💻 Code

interface P<T> {
  then: (onfulfilled: (value: T) => unknown) => unknown;
}

interface PConstructor {
  new <T>(executor: (resolve: (value: T) => void) => void): P<T>;
}

declare var P: PConstructor;

declare function foo1<T>(x: () => P<{ default: T }>): T;

const result1 = foo1(() => {
  return new P((resolve) => {
    resolve;
  });
});

type WithDefault<T> = { default: T };

declare function foo2<T>(x: () => P<WithDefault<T>>): T;

const result2 = foo2(() => {
  return new P((resolve) => {
    resolve;
  });
});

declare function foo3<T>(x: () => P<[T]>): T;

const result3 = foo3(() => {
  return new P((resolve) => {
    resolve;
  });
});

declare function foo4<T>(x: () => P<{ default: { prop: T } }>): T;

const result4 = foo4(() => {
  return new P((resolve) => {
    resolve;
  });
});

declare function foo5<T>(x: () => P<{ default: [T] }>): T;

const result5 = foo5(() => {
  return new P((resolve) => {
    resolve;
  });
});

🙁 Actual behavior

Only foo2 and foo3 have errors and we can see that their inner resolves reference never

🙂 Expected behavior

All of those should consistently error and resolve should be typed as (value: unknown) => void. Specifically, foo1 and foo2 are the almost the same signatures but foo2 is using a type alias in its declaration which changes the inference behavior. This is strong indication of the bug here

Additional information about the issue

No response

Commencez par reproduire l’exemple de Playground et comparer l’inférence des paramètres contextuels de foo1 à foo5, en particulier les instanciations d’objets anonymes par rapport au type alias WithDefault. Suivez le chemin d’inférence de types qui produit le type resolve interne ; c’est terminé lorsque les cinq cas signalent systématiquement des erreurs et que la résolution de type est signalée comme acceptant unknown.