added initial POC for flow support

[torifat]

POC for issue #324

$ npm run create-react-app my-app
$ cd my-app
$ vim .flowconfig # copy template from: https://github.com/facebookincubator/create-react-app/blob/master/template/README.md#adding-flow
$ npm start

Instead of vim .flowconfig, you can do wget https://gist.githubusercontent.com/torifat/756443d1bab62abda5f87c3ca2c90dc8/raw/ab2464634e3b0cd873d0ff302a83a5097964276f/.flowconfig too.

Sample App.js:

/* @flow */
import React, { Component } from 'react';
import logo from './logo.svg';
import './App.css';

Math.pow('1212');

class App extends Component {
  render() {
    return (
      <div className="App">
        <div className="App-header">
          <img src={logo} className="App-logo" alt="logo" />
          <h2>Welcome to React</h2>
        </div>
        <p className="App-intro">
          To get started, edit <code>src/App.js</code> and save to reload.
        </p>
      </div>
    );
  }
}

export default App;

Sample Output:

[ghost]

Thank you for your pull request and welcome to our community. We require contributors to sign our Contributor License Agreement, and we don't seem to have you on file. In order for us to review and merge your code, please sign up at https://code.facebook.com/cla - and if you have received this in error or have any questions, please drop us a line at cla@fb.com. Thanks!

[ghost]

Thank you for signing our Contributor License Agreement. We can now accept your code for this (and any) Facebook open source project. Thanks!

[gaearon]

This is very nice!

[gaearon]

cc @thejameskyle, I would love if someone from the Flow team could look at this and offer what can be improved in this implementation (webpack “loader” is like a browserify transform). Here’s a popular TypeScript loader for comparison.

[torifat]

I would love some pointers from Flow team. The current implementation in not optimal and also will hide errors if the mainFile doesn't match with the resource files. I will keep improving it throughout the week.

[kasperpeulen]

I tried it out last couple of days, seems to work fine 👍

[gabriel-laet]

@torifat @gaearon What I've noticed playing around with flowtype-loader in a larger codebase is that apparently calling flow status for each file is pretty slow. Maybe the ideal impl is call flow status once, cache and report errors for each file.

[torifat]

@gabriel-laet You are right. I hacked that in a night for POC. If you check the TODO section of README then you will find Fix performance issue (parse flow output once). I was in vacation and just get back today. If you want contribute you can give it a hand. Or, I will try to give it some time next week.

[gabriel-laet]

@torifat 👍 I will try to find some time and help on the performance issue

[jamiebuilds]

Hey @torifat thanks for taking the time to do this, I'd like to chat about it some more. Does Twitter DMs work for you?

[torifat]

@thejameskyle yes, it will do.

[ccorcos]

Hmm. I'm not sure we should even use a webpack loader. Using the flow-ide package, I get errors inline in my editor as I code. Then we can just run flow before we run our test suite...

[gaearon]

@ccorcos Editor integrations are great for sure but there’s a much wider reach when you build something in, as opposed to making it available via IDE plugins.

[ccorcos]

True... What additional features would you like to see that the typescript loader offers that this flow loader doesn't?

[gaearon]

I'm closing because unfortunately it doesn't appear like Flow team is interested in Create React App or Webpack integration, and there's no sense in keeping this hang here forever.

[jamiebuilds]

@gaearon that isn't true, I asked you to merge this over a month ago.

[jamiebuilds]

Please reopen this. In my opinion, it's ready to be merged, if you disagree let me know.

[torifat]

@thejameskyle need to update the implementation.

[gaearon]

Sorry, I didn't see that message from you or maybe misunderstood.
This PR has pretty fundamental issues like torifat/flowtype-loader#4.