Create-react-app: [ESLint] Support .eslintignore in project root

[mjackson]

Is your proposal related to a problem?

ESLint is trying to lint some pre-built files that I dropped into my src directory, but it's finding "errors", and causing the build to fail.

Describe the solution you'd like

I want to be able to drop a .eslintignore file in my create-react-app root and have it Just Work ™️.

Describe alternatives you've considered

I tried using the EXTENDS_ESLINT env variable and overriding specific rules in my custom src/.eslintrc.js, but overriding each rule one at a time, but it's easy to miss some. I really just don't want ESLint even trying to lint the file at all.

Additional context

I'm working on a new version of React Router and it'd be nice if people could just drop react-router.production.js into their src directory and see everything work w/out having to worry about ESLint failing. Google Closure Compiler does some interesting things to our built code that ESLint complains about.

I already submitted #8063 which fixes the main issue, but it'd be nice to just disable ESLint completely on any given file, like you'd be able to in a normal ESLint project.

[ianschmitz]

Hey @mjackson. Your .eslintignore should work when EXTEND_ESLINT=true correct?

[mjackson]

That's what I'd hope @ianschmitz, but CRA currently doesn't work that way. I made a small repro in case you'd like to check it out. Here's the commit that introduces the "bug". Because CRA considers this an error, this app won't run.

https://github.com/mjackson/eslint-bug-cra-demo/commit/d605a4214aa2fb9b995fbc6a58227cbb0d2de4c2

[miraage]

@mjackson I believe there is a typo in the environment variable.

[mjackson]

Ah, you're right @miraage. Thank you for taking a look. Indeed, it works as @ianschmitz described. Sorry for the false alarm!

[ianschmitz]

No problem! Our plan is to make this the default behavior in v4 where it will just work as you say, but for v3 we made it an opt in.

[stephenmcm]

Sorry to bump a closed issue but can I get an explain like I'm 5, on the set up for this? I can't get .eslintignore to be read no matter what I try.

Setting start in package.json to "start": "EXTEND_ESLINT=true react-scripts start",
Add .eslintignore to the root of the project with **/*.js
Run npm run start

My expected output is build successful with no warnings or errors. My actual result is build with warnings. I've tried this in both existing projects and a fresh project which I've created a repo for here:
https://github.com/stephenmcm/cra-eslintignore

From my testing so far I can see that EXTEND_ESLINT=true does allow extension of eslint configs but doesn't seem to read the .eslintignore.

Is there something painfully obvious I'm missing?

[ianschmitz]

@stephenmcm that should work. Can you open a new issue so we can track?