instantiation expression usage leading to an invalid d.ts file generation #60758
Description
🔎 Search Terms
partial function generic application, function generic variant from another function, instantiation-expressions
🕗 Version & Regression Information
- This changed between versions 5.6.2 and 5.7.2
⏯ Playground Link
💻 Code
type SomePropertyKeys = ReadonlyArray<PropertyKey>
type At<A extends ReadonlyArray<unknown>, I extends number = number> = A[I]
export function mainKeyGuard<
K extends readonly [PropertyKey, ...SomePropertyKeys],
>(
keys: K,
): <T extends object>(
value: T,
) => value is Extract<T, Record<At<K, 0>, unknown>> {
return <T extends object>(
value: T,
): value is Extract<T, Record<At<K, 0>, unknown>> => {
return keys[0] in value
}
}
type Foo = { foo1: string, foo2: string }
type Bar = { bar1: string, bar2: string }
type FooBar = Foo | Bar
const barKeys = ['bar1', 'bar2'] as const
export const isBar = mainKeyGuard(barKeys)<FooBar>🙁 Actual behavior
Starting with the v5.7.2, the generated d.ts file declares isBar as a function which reference a missing generic type T, so an error is raised
export declare const isBar: (value: FooBar) => value is Extract<T, Record<At<K, 0>, unknown>>;🙂 Expected behavior
I would expect the isBar function d.ts declaration to not reference a missing generic type T.
Previously, the generated d.ts file behaved like the following
export declare const isBar: (value: FooBar) => value is Bar;Additional information about the issue
The title mentions "instantiation expression" but I'm not totally sure about how the involved feature is actually named