feat: emit warning when .eslintignore file is detected

[snitin315]

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What is the purpose of this pull request? (put an "X" next to an item)

[ ] Documentation update
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What changes did you make? (Give an overview)

Fixes #17831

Is there anything you'd like reviewers to focus on?

Now a lot of warnings are polluting the test command output

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[mdjermanovic]

Now a lot of warnings are polluting the test command output

Can we maybe move the patterns into ignorePatterns in the config file and remove the .eslintignore file?

[nzakas]

I'm pretty sure there are tests that rely on .eslintrc.js and .eslintignore, which is why they're still present in the repo even though we aren't using them as part of our dev setup.

[mdjermanovic]

I'm pretty sure there are tests that rely on .eslintrc.js and .eslintignore, which is why they're still present in the repo even though we aren't using them as part of our dev setup.

In #17204, we updated tests to not rely on this project's eslint config files. I'm not 100% sure about the .eslintignore file and if some new tests didn't slip in in the meantime, but we could try.

[snitin315]

Can we maybe move the patterns into ignorePatterns in the config file and remove the .eslintignore file?

I'll try this and see how much we can reduce such warnings.

[snitin315]

I've removed the root .eslintignore, and the warning logs have been reduced by ~90. But there are still warnings from tests relying on the presence of test/fixtures/.eslintignore & --ignore-path which doesn't work with flat config. Should we remove/migrate these tests too?

[nzakas]

We still need to have some tests that rely on .eslintignore because we are still supporting that file in eslintrc mode in v9.x. (In theory, we could remove them, but then we wouldn't know if we broke eslintrc mode in some way. I don't think that's a good idea.)

[mdjermanovic]

We could suppress these warnings in test files that are producing them, for example this way:

sinon.stub(process, "emitWarning").withArgs(sinon.match.any, "ESLintIgnoreWarning").returns();
process.emitWarning.callThrough();

[snitin315]

I've updated the corresponding tests to suppress the warnings.

[mdjermanovic]

Now that we have found a way to suppress the warnings while running tests, what do you think about restoring the .eslintignore file for now? I ask because it turns out that over a hundred tests used this file, and while it appears that they're passing without it, it doesn't necessarily mean that they're still testing what they were intended to, so it might be good that we check each of them at some future point, and then remove the .eslintignore file.

[snitin315]

That makes sense, I think we can restore the .eslintignore file for now.

[snitin315]

Done!

[nzakas]

LGTM. Would like @mdjermanovic to verify before merging.

[bmish]

Nice! Thanks for picking this up.

[mdjermanovic]

Looks good, just two small suggestions about the tests.

[mdjermanovic]

LGTM, thanks!