potential bug related to generics

Bug Report

🔎 Search Terms

generics
pipe
functional programming

🕗 Version & Regression Information

5.2.0-dev

• This is the behavior in every version I tried

⏯ Playground Link

Playground link with relevant code

💻 Code

export type Func = (..._: any[]) => unknown;

export type Unary<Input, Output> = (_: Input) => Output;

export type Tail<L extends unknown[]> = L extends
  readonly [unknown, ...infer LTail] ? LTail
  : L;

type UnaryFn<A, R> = (a: A) => R;
type Arg<F> = F extends UnaryFn<infer A, unknown> ? A : never;
type Res<F> = F extends UnaryFn<any, infer R> ? R : never;

type ValidCompose<F1, F2> = Res<F1> extends (Arg<F2> | Promise<Arg<F2>>) ? F1
  : (arg: Arg<F1>) => Arg<F2>;

type ValidPipe<FS> = FS extends [infer F1, infer F2, ...infer Rest]
  ? [ValidCompose<F1, F2>, ...ValidPipe<[F2, ...Rest]>]
  : FS;

export const pipe = <Fs extends Func[]>(  ...fs: ValidPipe<Fs>) => {}

(<T, Fn extends (x: T) => number>(f: Fn) => {
  const g = (x: T) => x;
  const h = (_: T) => 1;
  pipe(g, f);  // This gives a typing error.
  pipe(g, h);  // This works fine.
});

🙁 Actual behavior

The first pipe invocation results in a typing error.

🙂 Expected behavior

None should have an error, because the generic typing ensures everything is in order.

Inizia con il TypeScript Playground collegato e riduci l’esempio generico di pipe attorno a ValidCompose, ValidPipe e alle due invocazioni di pipe. Analizza il comportamento del controllo dei tipi per la funzione generica f rispetto a h; il lavoro è completo quando entrambe le chiamate superano il controllo dei tipi senza errori, preservando i vincoli generici riportati.