feat(rule-tester): switched to flat config

[JoshuaKGoldberg]

BREAKING CHANGE:
Switches RuleTester from legacy configs to flat configs.

PR Checklist

• Addresses an existing open issue: fixes Enhancement(rule-tester): FlatRuleTester -> RuleTester #9017
• That issue was marked as accepting prs
• Steps in Contributing were taken

Overview

Switches the internals of our forked RuleTester to work with new Linter({ configType: 'flat' }); instead of configType: 'eslintrc'. This is a pretty substantial breaking change internally:

• this.#linter is no longer able to defineRule() ad hoc; instead, the config: TesterConfigWithDefaults has to have plugins including the rule.
• Because the @/ plugin can't be redefined, a @rule-tester/ prefix is added in front of rule names.
• Per flat config, any parser, parserOptions, and other language-specific settings are moved to languageOptions.
  • This caused a lot of churn in our test files
• Per flat config, parser has to be the actual parser, not a string descriptor.
  • As a convenience, I formally defaulted it to our parser
  • I went ahead and removed all the redundant parser: '@typescript-eslint/parser', parserOptions: { sourceType: 'module' }, and other seemingly unnecessary options from our test files
• Marks the @typescript-eslint/utils RuleTester re-export as deprecated

I think we'll want to follow this up with added info in the v8 beta blog post. See our packages/eslint-plugin(-internal)/**/*.test.ts file changes. There's a fair amount users will have to do:

• Nest lib, parser, parserOptions, sourceType, and any other parser options inside languageOptions
• Switch parser from a string to the actual parser
• The default ecmaVersion and sourceType are now 'latest' and 'module', respectively

💖

[typescript-eslint]

Thanks for the PR, @JoshuaKGoldberg!

typescript-eslint is a 100% community driven project, and we are incredibly grateful that you are contributing to that community.

The core maintainers work on this in their personal time, so please understand that it may not be possible for them to review your work immediately.

Thanks again!

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✅ Successfully ran 31 targets

• nx test eslint-plugin --coverage=false
• nx test typescript-estree --coverage=false
• nx test type-utils --coverage=false
• nx test typescript-eslint --coverage=false
• nx test utils --coverage=false
• nx run types:build
• nx test scope-manager --coverage=false
• nx test eslint-plugin
• nx test visitor-keys --coverage=false
• nx run repo-tools:postinstall-script
• nx test rule-schema-to-typescript-types --coverage=false
• nx test repo-tools --coverage=false
• nx test parser --coverage=false
• nx test ast-spec --coverage=false
• nx run-many --target=build --parallel --exclude=website --exclude=website-eslint
• nx test type-utils
• nx test visitor-keys
• nx test eslint-plugin-internal --coverage=false
• nx run-many --target=lint --parallel --exclude eslint-plugin
• nx test typescript-estree
• nx test typescript-eslint
• nx test utils
• nx test scope-manager
• nx test ast-spec
• nx test eslint-plugin-internal
• nx test parser
• nx test rule-schema-to-typescript-types
• nx test repo-tools
• nx run integration-tests:test
• nx run-many --target=typecheck --parallel
• nx run repo-tools:generate-configs

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[bradzacher]

Per flat config, any parser and parserOptions, and other language-specific settings are moved to languageOptions.

Thought: I wonder if we should have hoisted up our stuff / the common stuff to avoid churn. Cos this will mess with all the ecosystem as well. I know that was their intent but it is going to block plugins hard.

[JoshuaKGoldberg]

Per flat config, any parser and parserOptions, and other language-specific settings are moved to languageOptions.

Thought: I wonder if we should have hoisted up our stuff / the common stuff to avoid churn. Cos this will mess with all the ecosystem as well. I know that was their intent but it is going to block plugins hard.

Yeah I don't think we're in a good place to do anything here. +1 that this will be work for plugins, but:

• Switching our RuleTester from a rough drop-in to something noticeably different from the core config system would be a big step away from core
• Most plugins will just need to wrap some stuff in languageOptions

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.01%. Comparing base (ae980e3) to head (11c5c78).
Report is 8 commits behind head on v8.

Additional details and impacted files

@@            Coverage Diff             @@
##               v8    #9603      +/-   ##
==========================================
+ Coverage   88.00%   88.01%   +0.01%     
==========================================
  Files         401      401              
  Lines       13647    13637      -10     
  Branches     3965     3960       -5     
==========================================
- Hits        12010    12003       -7     
  Misses       1325     1325              
+ Partials      312      309       -3     

Flag	Coverage Δ
unittest	88.01% <ø> (+0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
packages/utils/src/eslint-utils/deepMerge.ts	89.47% <ø> (ø)
packages/utils/src/ts-eslint/Linter.ts	50.00% <ø> (ø)
packages/utils/src/ts-eslint/RuleTester.ts	50.00% <ø> (ø)
packages/utils/src/ts-eslint/SourceCode.ts	50.00% <ø> (ø)

... and 2 files with indirect coverage changes