Bug: [new config system] ignores does not work without files

[filetvignon]

Environment

Node version: 18.16.0
npm version: 9.6.4
Local ESLint version: 8.38.0
Global ESLint version: N/A
Operating System: Ubuntu 22.04 (WSL)

What parser are you using?

Default (Espree)

What did you do?

Configuration

[
  {
    rules: {
      "no-unused-vars": "error",
    },
  },
  {
    ignores: ["error.js"],
    rules: {
      "no-unused-vars": "warn",
    },
  },
];

./error.js and ./warn.js:

let unusedVar;

Then run eslint .

What did you expect to happen?

{cwd}/error.js
  1:5  error  'unusedVar' is defined but never used  no-unused-vars

{cwd}/warn.js
  1:5  warning  'unusedVar' is defined but never used  no-unused-vars

What actually happened?

{cwd}/error.js
  1:5  warning  'unusedVar' is defined but never used  no-unused-vars

{cwd}/warn.js
  1:5  warning  'unusedVar' is defined but never used  no-unused-vars

Link to Minimal Reproducible Example

https://github.com/filetvignon/eslint-bug-ignores

Participation

• I am willing to submit a pull request for this issue.

Additional comments

I set 2 configuration objects: one with a rule all files and another to change that rule for all files EXCEPT error.js.
I omitted the files property in these objects; although the documentation recommends using ignores with files, it states that this should work and omitting files should be the same as using files: '**/*'.

In reality, it works only if I explicitly set files in the second configuration object:

[
  {
    rules: {
      "no-unused-vars": "error",
    },
  },
  {
    files: ["**/*"],
    ignores: ["error.js"],
    rules: {
      "no-unused-vars": "warn",
    },
  },
];

[fasttime]

I am able to reproduce this. This is happening because configs without files are considered universal configs, and they are applied to all files regardless of ignores. I also find this behavior surprising, but I believe that it's there intentionally to allow excluding things like node_modules from linting. In this case we should update the documentation to mention that ignores works differently in a config without files.

Maybe @nzakas can advise the best course of action here.

[mdjermanovic]

This is a bug, the configuration object should not apply to file paths that match its ignores.

In this case we should update the documentation to mention that ignores works differently in a config without files.

There are two cases:

1. Configuration object has ignores and doesn't have any other keys. In this case, the object specifies which files should be ignored. Mentioned here: https://eslint.org/docs/latest/use/configure/configuration-files-new#globally-ignoring-files-with-ignores.
2. Configuration object has ignores and one or more other keys. This is a "normal" entry that specifies configuration for matching files. If it doesn't have files, it should work the same as if it had files: ["**/*"]. This is mentioned at the end of https://eslint.org/docs/latest/use/configure/configuration-files-new#excluding-files-with-ignores:

eslint/docs/src/use/configure/configuration-files-new.md

Lines 119 to 132 in 5ea15d9

	If `ignores` is used without `files` and any other setting, then the configuration object applies to all files except the ones specified in `ignores`, for example:
	```js
	export default [
	{
	ignores: ["**/*.config.js"],
	rules: {
	semi: "error"
	}
	}
	];
	```
	This configuration object applies to all files except those ending with `.config.js`. Effectively, this is like having `files` set to `**/*`. In general, it's a good idea to always include `files` if you are specifying `ignores`.

[fasttime]

Thanks for the clarification @mdjermanovic. Sometimes it's hard to know if it's the implementation that doesn't match the docs or vice-versa. That said, I find the headline of the example mentioned above confusing, as it should actually read (bold is my correction):

If ignores is used without files but with some other settings, then the configuration object applies to all files except the ones specified in ignores, for example:

As for the bug, it needs to be fixed in @humanwhocodes/config-array, although it would be also a good idea to add some unit tests here in eslint.

@filetvignon would you like to submit a pull request?

[mdjermanovic]

That said, I find the headline of the example mentioned above confusing, as it should actually read (bold is my correction):

If ignores is used without files but with some other settings, then the configuration object applies to all files except the ones specified in ignores, for example

Yes, I think we should fix that in the docs.

[nzakas]

Just catching up on this now. This does look like a bug, and the docs could be clearer, I'd suggest something more along the lines of this:

If ignores is used without files and there are other keys (such as rules), then the configuration object applies to all files except the ones specified in ignores, for example

[nzakas]

I pushed a new version of @humanwhocodes/config-array, but I won't have time to integrate into ESLint before traveling for next week.

[mdjermanovic]

I pushed a new version of @humanwhocodes/config-array, but I won't have time to integrate into ESLint before traveling for next week.

I can take this, but it seems that the new version 0.11.9 hasn't been released. The release workflow failed on npm ci:

https://github.com/humanwhocodes/config-array/actions/runs/4961978783/jobs/8879447925

[nzakas]

Sorry about that, should be published now.