Add support to new ESLint flat config

[Alex-Sokolov]

Now eslint-nibble finished with error when trying to run with new flat config

"lint": "eslint-nibble --config eslint.config.js . --ext .js,.ts,.vue",

https://eslint.org/docs/latest/use/configure/configuration-files-new

[IanVS]

Thanks for the heads-up. I'll try to add support soon, but if anyone wants to submit a PR that would be excellent.

[kobizz]

@IanVS any updates?

[IanVS]

I haven't had time to dig into it so far. If anyone is interested, please feel free. Or, if you're willing to set up a reproduction repo that I can use as a starting point, that would also be helpful.

[johannes-lindgren]

To me, it seems like it doesn't work without the flat config. I have an .eslintrc.cjs file with .eslintignore, and get this error:

(node:14980) ESLintIgnoreWarning: The ".eslintignore" file is no longer supported. Switch to using the "ignores" property in "eslint.config.js": https://eslint.org/docs/latest/use/configure/migration-guide#ignoring-files

I'm on eslint v8.56.0

[ljharb]

i mean, even in eslintrc, you should really be using ignorePatterns instead of an .eslintignore file - what happens if you make that change?

[johannes-lindgren]

@ljharb, I forgot to mention: it gave me another error:

throw new ESLintInvalidOptionsError(errors);
^

ESLintInvalidOptionsError: Invalid Options:

• Unknown options: extensions
• 'extensions' has been removed.

I don't have any extension option in my .eslintrc.cjs file, but perhaps it's somewhere in a plugin.

[ljharb]

What plugins are you using? not all plugins are compatible yet with flat config.

[johannes-lindgren]

I disabled all plugins, yet I get the error.

In this package, I am not using a flat config, hence why I didn't really expect and error message around that. I am migrating gradually in a monorepo. eslint-nibble used to work though, and I don't think I changed anything in this workspace

[IanVS]

@johannes-lindgren eslint-nibble always sets extensions (until I have time to cut a new version, at least). I think it used to be required when interacting directly with the eslint API, but I could be wrong.

I don't think extensions support was removed until v9 though, so since you mention you've got a monorepo, I wonder if perhaps version 9 of eslint is being pulled in from somewhere. If you're sure it's broken with v8 and standard config files, please create a minimal reproduction so I can investigate.

[johannes-lindgren]

@IanVS thanks for the swift reply; I was just about to post that I managed to work around the issue, and I think it's exactly what you suggested. In ESLint v9, the flat config file is the default. Though I didn't use ESLint v9 anywhere in the monorepo, when running eslint-nibble with npx, it somehow seems to resolve ESLint to version 9 (that's my guess at least). If I declare eslint-nibble indevDependencies, it works as expected.