FlowTyped HOCs across files

[kirkness]

I'm essentially trying to create a file with a reusable HOC called withNavbar, it is just a setStatic with a few defaults.

This may be a misunderstanding of mine, but I'm seeing the following and can't understand why;

./with-navbar.js

// @flow
import { setStatic } from 'recompose';

const withNavbar = (title: string) =>
  setStatic('navigationOptions', {
    headerTitle: title,
  });

export default withNavbar;

./screen.js

// @flow
import React from 'react';
import { compose, withStateHandlers, type HOC } from 'recompose';
import { Text } from '../styles/components';
import withNavbar from './with-navbar';

const Test = props => <Text>{props.num}</Text>;

const enhance: HOC<*, {}> = compose(
  withNavbar('MyCounter'),
  withStateHandlers({ num: 1 }, { onSetNum: () => (num: number) => ({ num }) })
);

export default enhance(Test);

When I remove withNavbar('MyCounter') OR move the code in ./with-navbar.js to the top of the screen.js file, I get all the inferred props. However with it, props are empty.

[istarkov]

You need to type withNavbar too

[kirkness]

Hey, @istarkov thanks for helping - could you elaborate? What is the reason that it works when the hoc is defined within screen.js and not when it's in a different file?

I've tried typing it but am still not seeing it pull through.

[istarkov]

It's how flow works, if something is used inside one file and not exported flow can infer function types.
But if function is exported, flow have no enough information how this function can be used (it's like deprecated * type which infered only within current file)
As I understand this is done by flow team for performance reasons.

In your case withNavbar have same return type as setStatic HOC<A, A> so you could define it as

/* @flow */

import { setStatic } from 'recompose';
import type { HOC } from 'recompose';

const withNavbar = <T>(title: string): HOC<T, T> =>
  setStatic('navigationOptions', {
    headerTitle: title,
  });

export default withNavbar;

[istarkov]

Also having that * is deprecated I would recommend to type Enhanced components as

const SomeComponentExt: React.ComponentType<EnhancedProps> = compose(
   hoc1, ..., hocN
)(SomeComponent)

export default SomeComponentExt;

[istarkov]

The best of above you don't need any type imports from recompose like import type {HOC}
for usual components

[istarkov]

As I understand this is done by flow team for performance reasons.

Also exported function can be used outside of your project so not only performance

[kirkness]

This is awesome thanks so much for clearing it up!

[FezVrasta]

How can I use setStatic without HOC?

const enhance = setStatic('foo', 'bar');

const Foo: ComponentType<{ children: Node}> = enhance(({ children }) => children);

console.log(Foo.foo); // Flow error,  property foo is missing in React.StatelessFunctionalComponent [1].

[istarkov]

@FezVrasta better to use resources like stack overflow as it already have answers on this, as it's the same how to type any react component with static fields
const Foo: { x: string } & React.ComponentType<{ blabla }> = Radio;

[FezVrasta]

Doesn't this nullifies all the automatic inference that should happen with the Recompose support for Flow? This stuff should be automatically inferred

[istarkov]

What exactly nulified in your case?

[FezVrasta]

That I have to manually specify the type of my final enhanced component. Other HOCs will automatically add the needed inferred types.

[istarkov]

What changed? You need to specify that type before in HOC, you need to specify it now.

[istarkov]

You need to specify type of your classes so it's all the same

[FezVrasta]

I don't know, it seems redundant.

Anyway your suggestion doesn't work, Flow complains:

Cannot assign `enhance(...)` to `Foo` because property `foo` is missing in `React.StatelessFunctionalComponent` [1] but exists in object type [2].

[istarkov]

Because setStatic type is wrong https://github.com/acdlite/recompose/blob/master/src/packages/recompose/index.js.flow#L174

must be something like

declare export function setStatic<A, KEY, VAL>(key: Key, value: VAL): ((React.ComponentType<A>) => {[KEY]: VAL} & React.ComponentType<A>) but need to be tested

[FezVrasta]

Thanks. I fixed the typo (Key => KEY) but it still doesn't work :-(

[istarkov]

flow is magic ;-)
To be clear: in no case I'm big specialist of flowtype, most of time it works well for me, but I also experiencing problems with it, strange errors, and all that magic. Usually if I see errors like above I use "poke method" (метод тыка) so I try different hacks which worked for me in the past, I read flow issues, stack overflow, and do same stuff as other people.
I will look later. The problem of "poke" method that it doesn't give any guaranty that I'll find something.

[istarkov]

For a fast fix you can cast to any and then to your type
const Blabla: MyType = (anything: any);

[FezVrasta]

Thanks, it's really discomforting to see that one of the most popular React libraries, maintained by one of the Facebook guys, has so bad Flow support, technology built at Facebook 😥

[istarkov]

Current maintaineers are not facebook employes. Mostly I wrote flow support, and having that I never used setStatic it has problems. Also & types were always problematic in flow, and in most cases broke all. Most of hocs works well with flowtype as I use flowtype and recompose on daily basis.
I dont think that flow support bad in recompose

[FezVrasta]

I see, I'd love to be good enough in Flow to contribute to it.

Maybe moving the types into the library may help to get more contributions? Setting up flow-typed is pretty complex and time intensive.

[istarkov]

Types are already in library see
here is type definitions https://github.com/acdlite/recompose/blob/master/src/packages/recompose/index.js.flow#L174

here is type tests
https://github.com/acdlite/recompose/tree/master/src/packages/recompose/__tests__/types

library itself is not typed, but at the moment I wrote typedefs it wasn't possible because of some flow issues.

[istarkov]

running in project root

yarn flow

you get the all flowtype tests, editor support vscode, nuclide atom is also work well in any file marked with /* @flow */ in project

[istarkov]

@FezVrasta see #678
So type I proposed, works, just can't be used inside compose.
And even I'm not a big specialist in flowtype I can give 99% guaranty that it is impossible with current flowtype to make compose work with setStatic inside (without breaking inference for all the hocs).

[FezVrasta]

Ok thanks for all the info and for your time!

[istarkov]

Also to be fair, last months I use render props components more and more like https://github.com/renatorib/react-powerplug and flow was one of the most thing which affects my move into render props world. Much more easier to use such components with flow, in a lot of cases you dont need to type anything. So can highly recommend at least library above