ExtractReturn type is any

[dfroger]

I have problem with the ExtractReturn helper as reproduced in this example code.

In redux.js, action has type any, while it should be the returned type of foo.

Tested with flow 0.83.0, there is no error message.

Thanks for your yelp.

actions.js:

// @flow

import type { A } from './a';

import * as actions from './actions';

export type ExtractReturn<Fn> = $Call<<T>((...Iterable<any>) => T) => T, Fn>;

export const FOO: 'FOO' = 'FOO';
export const BAR: 'BAR' = 'BAR';

export const foo = () => ({
    type: FOO,
    foo: 42
})

export const bar = () => ({
    type: BAR,
    bar: 42
})

export type Action =
    | ExtractReturn<typeof actions.bar>
    | ExtractReturn<typeof actions.foo>;

a.js:

// @flow

import * as actionTypes from './actions';
import type { Action } from './actions';

export type A = string;

export const reducer = (action: Action) => action.type === actionTypes.FOO ? 1 : 2;

redux.js:

// @flow

import * as actionTypes from './actions';
import type { Action } from './actions';

export const reducer = (action: Action) => {
    if (action.type === actionTypes.FOO) console.log(action.x);  // action is typed any here
};

[MartinCerny-awin]

I am having the same issue and it looks like that it is related to import bug mentioned in #6797 (comment) and probably to #4312

When I use type extracted using ExtractReturn in the same file it is correctly typed, but when I import it in the different file, it is exported as any.

[dfroger]

@MartinCerny-awin Thanks for this very usefull feedback! I'll keep an eye on these issues...

[Eugene-Musika]

It works if add * as return type to foo and bar actions like so:

export const foo = (): * => ({
    type: FOO,
    foo: 42
})

export const bar = (): * => ({
    type: BAR,
    bar: 42
})

Hope it will help someone.
But still I think it's a bug. And it reproduces even in v0.109.0

[dfroger]

Interessing! By the way, I didn't updated this issue, as I'm no more working on web development.

[SamChou19815]

We now have ReturnType