no-unused: false positive with substitution type inside mapped type

[ajafff]

trafficstars

type Values<T> = T extends {[K in keyof T]: infer U} ? U : never;

U is marked as unused but is actually referenced in the then branch of the conditional type

[InExtremaRes]

It's similar but not exactly the same:

type Foo<T> = T extends { new (a: infer A): any } ? A : never;

A is marked as unused.

We can make and indirection, though:

interface Baz<A> { new (a: A): any }
type Bar<T> = T extends Baz<infer A> ? A : never;

[ifiokjr]

I think in general it affects many inferred types.

/**
 * Pick the Nth Param for any function with the first parameter marked by the 0 index.
 */
export type NthParam<GFunction extends AnyFunction, GIndex extends number> = GFunction extends (
  ...args: infer GArgs // => Flagged as unused
) => any
  ? GArgs[GIndex]
  : never;

The linter warns me that GArgs is unused.