ParamTypes issue

[sirian]

As I mentioned in microsoft/TypeScript#25660 (comment) and in microsoft/TypeScript#21316 (comment)
without inversed check you got wrong result

declare function argTypes<F extends Function>(f: F): ParamTypes<F>

// $ExpectType []
argTypes(() => true); // Expected type to be:  [] got:  {}

// $ExpectType [string, boolean | undefined]
argTypes((x: string, y?: boolean) => true); // Expected type to be:  [string, boolean | undefined] got:  [string]

[pelotom]

Yeah, makes sense. Would you like to make a PR?

[sirian]

Sorry, have no time. That's my current scratch if smbd will)

type Constructor<T = any, A extends any[] = any[]> = new (...args: A) => T;
type AnyFunction<R = any, A extends any[] = any[]> = (...args: A) => R;
type ArgTypes<F> = 
    F extends AnyFunction<any, infer T> ? T :
    F extends Constructor<any, infer U> ? U :
    F extends Function ? any[] : never;
type ArgCount<F> = ArgTypes<F> extends infer R
    ? (R extends any[] ? R["length"] : never)
    : never;

[pelotom]

Sorry, have no time.

Welcome to the club 🙂

[fbartho]

We're all here, but we can't stay to chat. No time.