feat: add rule test deprecation warnings: fn-style rules/missing schema

[bmish]

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

[ ] Documentation update
[ ] Bug fix (template)
[ ] New rule (template)
[ ] Changes an existing rule (template)
[ ] Add autofix to a rule
[ ] Add a CLI option
[X] Add something to the core
[ ] Other, please explain:

What changes did you make? (Give an overview)

Prepares for upcoming breaking changes in ESLint v9 to disallow function-style rule and rules with options that are missing a schema.

Adds the deprecation warnings mentioned in the RFC (eslint/rfcs#85).

These deprecation warnings will help alert plugin authors that they need to update their rules. They are only visible when running rule tests and not to end-users who just use the rules.

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

1. Any suggestions on how to test these messages to stdout?
2. Is simply replicating these in flat rule tester right for now? How can I manually test the flat rule tester? I manually tested the normal rule tester. See comments.
3. Should I switch to process.emitWarning() (see comments)?

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[mdjermanovic]

2. Is simply replicating these in flat rule tester right for now? How can I manually test the flat rule tester? I manually tested the normal rule tester.

I think it isn't necessary to add deprecation warnings to FlatRuleTester if we are planning eslint/rfcs#85 for ESLint v9, as FlatRuleTester won't be used in production before ESLint v9,

[bmish]

@mdjermanovic that's fair. Should I just remove the changes to FlatRuleTester then? Or should I leave them for consistency since we will want to replace these warnings with permanent asserts in the next major version.

[mdjermanovic]

since we will want to replace these warnings with permanent asserts in the next major version

Is it necessary to have these checks in RuleTester in the next major version? Per the RFC, they will be implemented in the core. If it throws anyways, it seems we don't need to duplicate checks in RuleTester.

[bmish]

@mdjermanovic good point, removed from flat rule tester.

[mdjermanovic]

1. Any suggestions on how to test these messages to stdout?

If it helps, we have some deprecation warnings in eslintrc and the tests are here.

But there we're using process.emitWarning(). I'm not sure what the advantages are over console.warn and which way would be more appropriate for these warnings.

[bmish]

I added tests for console.warn.

However, it looks like process.emitWarning() and lib/shared/deprecation-warnings.js would be a bit more of a formalized and centralized means for managing these deprecation warnings. So while my new deprecation warnings are temporary and should be removed later this year with the next major release, I could still try to switch over to those existing means if desired.

[mdjermanovic]

This assumes that the warning message will be logged right after the test title, but that doesn't have to be the case.

For example, if you run mocha with -R progress, it would look like this:

[▬▬..........................................................................]DEPRECATION WARNING: This test case specifies `options` but the rule is missing `meta.schema` and will stop working in ESLint v9. Please add `meta.schema`: https://eslint.org/docs/developer-guide/working-with-rules#options-schemas This lint rule can assist with the conversion: https://github.com/not-an-aardvark/eslint-plugin-eslint-plugin/blob/main/docs/rules/require-meta-schema.md
  [▬▬▬.........................................................................]DEPRECATION WARNING: This test case specifies `options` but the rule is missing `meta.schema` and will stop working in ESLint v9. Please add `meta.schema`: https://eslint.org/docs/developer-guide/working-with-rules#options-schemas This lint rule can assist with the conversion: https://github.com/not-an-aardvark/eslint-plugin-eslint-plugin/blob/main/docs/rules/require-meta-schema.md
DEPRECATION WARNING: This test case specifies `options` but the rule is missing `meta.schema` and will stop working in ESLint v9. Please add `meta.schema`:
https://eslint.org/docs/developer-guide/working-with-rules#options-schemas This lint rule can assist with the conversion: https://github.com/not-an-aardvark/eslint-plugin-eslint-plugin/blob/main/docs/rules/require-meta-schema.md
  [▬▬▬▬........................................................................]DEPRECATION WARNING: This test case specifies `options` but the rule is missing `meta.schema` and will stop working in ESLint v9. Please add `meta.schema`: https://eslint.org/docs/developer-guide/working-with-rules#options-schemas This lint rule can assist with the conversion: https://github.com/not-an-aardvark/eslint-plugin-eslint-plugin/blob/main/docs/rules/require-meta-schema.md
  [▬▬▬▬▬.......................................................................]DEPRECATION WARNING: This test case specifies `options` but the rule is missing `meta.schema` and will stop working in ESLint v9. Please add `meta.schema`: https://eslint.org/docs/developer-guide/working-with-rules#options-schemas This lint rule can assist with the conversion: https://github.com/not-an-aardvark/eslint-plugin-eslint-plugin/blob/main/docs/rules/require-meta-schema.md
DEPRECATION WARNING: This test case specifies `options` but the rule is missing `meta.schema` and will stop working in ESLint v9. Please add `meta.schema`:
https://eslint.org/docs/developer-guide/working-with-rules#options-schemas This lint rule can assist with the conversion: https://github.com/not-an-aardvark/eslint-plugin-eslint-plugin/blob/main/docs/rules/require-meta-schema.md
...

The problem is that there's no info about which rule is the cause of the warnings. We could add ruleName to the message. Also, it might be good to log the warning only once per rule (not for each test case that has options)?

[mdjermanovic]

I think we shouldn't log the warning if item.options is an empty array, as that's basically the same as if no options had been passed.

[mdjermanovic]

However, it looks like process.emitWarning() and lib/shared/deprecation-warnings.js would be a bit more of a formalized and centralized means for managing these deprecation warnings. So while my new deprecation warnings are temporary and should be removed later this year with the next major release, I could still try to switch over to those existing means if desired.

process.emitWarning seems to be a Node API designed for use cases like this one, so it's probably right to use it instead of console.warn.

As for lib/shared/deprecation-warnings.js, I'm not sure if it is usable for this purpose, as it looks like it was designed for warnings related to configuration files.

[snitin315]

@bmish are you still working on this? If not, can I take over this PR?

[bmish]

@snitin I definitely want to see this work completed. If you want to attempt it, could you open a separate PR to do so? If I can find time to continue on my PR, I'll post here.

[bmish]

Closing in favor of #16063.