π Search Terms
silent never type return type inference alias propagating anonymous object
π Version & Regression Information
- This is the behavior in every version I tried
β― Playground Link
https://www.typescriptlang.org/play/?ts=6.0.0-dev.20250827#code/JYOwLgpgTgZghgYwgAgAoB4AqA+ZBvAKGWTAAsIQAuZACgHsQYBXAGxmBZYgBNqaA3OCyYRqmAJTIAvLiYgA1iDoB3EJJnI5ilSADcBAL4ECoSLEQpUAYQYBnMFCYIwdKPiLIQEZcizYaEAAeEAhMLlB8UBC2dCz8orSCwgkS0rj8dMDc6umZ2dQYOPpGBNwhLHBRyIJuqAU2IPaOzq76peWVKMwgzsAMyDB0dACMfjSBfDlo6HjIZfCsYGLIBtjiYm0IdmDIUbaLw9IDQ8M0NFOExFFgTFAgnt5oZ3ux8RceV9GvEPrExAD0-2QAD0APweAziYpQ4xgACeAAcUAB1YBkAAiEAWLDAfiOs3mcEWywMbTKCAqVW6vX6gzoACYxhNaFMMKiMViiTi-GsNsYto0dntFvSjnT6Wd3p8bncHj5UM8vnEIFK-i9lb8-oCQeDiJDoWSOlS5DT7nSAMxMyZpaYAbUwAF1echMJttrtootzWKhubJTbLh6ZfcvPLFTFlarPhH4pqAUCwRCYfrjOTKV0TWA+mahgAWK0sm0YAmc4n4ZAIqB0BEklbO13893CnG5n10XP+jSB663EOPBU0dVvAMfD0xn6j7WJvXJmHtCmdAaZ7PHOgAVgL5yLMzmpZx1HtDrr6xdbsFY8Wa7ba87uG7EGDcqeg6Vw67o6HE7+yCnupWs90IA
π» 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;
});
});
π Actual behavior
Only foo2 and foo3 have errors and we can see that their inner resolves reference never
π 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
π Search Terms
silent never type return type inference alias propagating anonymous object
π Version & Regression Information
β― Playground Link
https://www.typescriptlang.org/play/?ts=6.0.0-dev.20250827#code/JYOwLgpgTgZghgYwgAgAoB4AqA+ZBvAKGWTAAsIQAuZACgHsQYBXAGxmBZYgBNqaA3OCyYRqmAJTIAvLiYgA1iDoB3EJJnI5ilSADcBAL4ECoSLEQpUAYQYBnMFCYIwdKPiLIQEZcizYaEAAeEAhMLlB8UBC2dCz8orSCwgkS0rj8dMDc6umZ2dQYOPpGBNwhLHBRyIJuqAU2IPaOzq76peWVKMwgzsAMyDB0dACMfjSBfDlo6HjIZfCsYGLIBtjiYm0IdmDIUbaLw9IDQ8M0NFOExFFgTFAgnt5oZ3ux8RceV9GvEPrExAD0-2QAD0APweAziYpQ4xgACeAAcUAB1YBkAAiEAWLDAfiOs3mcEWywMbTKCAqVW6vX6gzoACYxhNaFMMKiMViiTi-GsNsYto0dntFvSjnT6Wd3p8bncHj5UM8vnEIFK-i9lb8-oCQeDiJDoWSOlS5DT7nSAMxMyZpaYAbUwAF1echMJttrtootzWKhubJTbLh6ZfcvPLFTFlarPhH4pqAUCwRCYfrjOTKV0TWA+mahgAWK0sm0YAmc4n4ZAIqB0BEklbO13893CnG5n10XP+jSB663EOPBU0dVvAMfD0xn6j7WJvXJmHtCmdAaZ7PHOgAVgL5yLMzmpZx1HtDrr6xdbsFY8Wa7ba87uG7EGDcqeg6Vw67o6HE7+yCnupWs90IA
π» Code
π Actual behavior
Only
foo2andfoo3have errors and we can see that their innerresolves referenceneverπ Expected behavior
All of those should consistently error and
resolveshould be typed as(value: unknown) => void. Specifically,foo1andfoo2are the almost the same signatures butfoo2is using a type alias in its declaration which changes the inference behavior. This is strong indication of the bug hereAdditional information about the issue
No response