[react-scripts] Do not lint *.bs.js files, generated by BuckleScript

[emmenko]

Summary

This PR introduces a small change in the eslint rule of webpack.config to exclude files ending with the suffix *.bs.js (which are compiled files generated by BuckleScript).

NOTE: I'm no RegEx expert, so if someone has a better suggestion about the test rule feel free to leave a comment 🙏

Background

When working on a React project which includes fully or partially ReasonML, you need BuckleScript to generate the compiled JS sources. When you have the in-source option active you will get the compiled JS sources (*.bs.js) next to the Reason source file.
Those files will therefore "live" inside the src folder, causing eslint to print some warnings:

This is a bit annoying and can simply be "solved" by telling eslint to ignore those files.

Wait, ReasonML? What about reason-scripts?

As you might know, there is a package called reason-scripts which is basically a "clone" of react-scripts, with some things adapted to compile Reason files out of the box (e.g. entry point index.re instead of index.js).

However, as I pointed out in this issue, I don't think it's necessary to have reason-scripts in the first place.
@rrdelaney also pointed out (correctly if I'm wrong) that bs-loader should not be included in the package anymore.
In fact, you can run the BuckleScript compiler in watch mode as a parallel process, next to react-scripts start. This way you don't need the loader at all and you can simply use the "normal" react-scripts package.

"scripts": {
  "start": "npm-run-all --parallel start:bsb start:app",
  "start:app": "react-scripts start",
  "start:bsb": "bsb -make-world -w",
}

Anyway, this is another story...

Btw, this change will need to be made in reason-scripts as well.

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Hopefully this gives you enough background/context to understand this change.
I'm open to any feedback/suggestion.

Thanks 🙏

[gaearon]

I don't think it makes sense for all people who eject to end up with this configuration as it serves a very narrow use case.

[emmenko]

I understand. However there is no way (as far as I know) to use a .eslintignore as it will get ignored (see #2115).

Do you have any other suggestion to tackle this case?

[emmenko]

Btw, if that's the only concern I guess we can simply annotate those extra lines with @remove-on-eject-begin / @remove-on-eject-end 🤔

Update: if you still use Reason and eject you would need to "re-add" those lines back in, so it doesn't help much anyway.

[gaearon]

I don't really see us doing this. The config is already complex enough after ejecting, and we need to be very careful about adding things there. Instead I'd suggest doing something to automatically inject // eslint-ignore or similar.

[emmenko]

Hmm so is react-scripts not meant to be used for Reason projects?