Add support for ESLint v9

[gund]

Add support for ESLint v9 while maintaining backwards compatibility with all previously supported ESLint versions.

Closes #78

This PR is cannot be finished until:

• Library is migrated to ESLint v9 in BC way
  • Migrate context.getAncestors() API usages
  • feat: add plugin meta and support typescript-eslint@7 #86
• Library is passing all tests
• BC test is added to make sure v8 still works
• Upstream dependencies add support for ESLint v9
  • typescript-eslint

[piotr-cz]

It looks like typescript-eslint is supporting flat configs now:

• https://typescript-eslint.io/getting-started#step-2-configuration
• ESLint v9 Support typescript-eslint/typescript-eslint#8211 (comment)

[Noumanluckey8057]

typescript-eslint/typescript-eslint#8211 (comment)

[JoshuaKGoldberg]

👋 @gund are you still planning on working on this soon?

[JoshuaKGoldberg]

As in: I'm happy to hop in and write a PR, but don't want to step on your toes. 🙂

[liquidg3]

@JoshuaKGoldberg - thought I was commenting on this earlier 😂 - hoping you can hop in and get this over the line if @gund is tied up! Thanks to you both for the hard work!

[karlhorky]

@gund now that ESLint v9 is out and typescript-eslint/typescript-eslint#8211 is closed in upstream, would you consider finishing and publishing this PR? (or publishing a pre-release version?)

As an alternative, there is also apparently an open proposal in typescript-eslint about a new rule marking @deprecated as a problem:

• Rule proposal: Warn when deprecated APIs are used (eslint-plugin-deprecation) typescript-eslint/typescript-eslint#8988

[Pietrucci-Blacher]

Hi @gund, any updates about a future release for ESlint V9 ? 👀

[SimonSchick]

Hey @gund we are looking to move to eslint v9 but this is the only remaining plugin really holding us back.
Are there incentives we can offer to move this forward?

[karlhorky]

For anyone wanting a rule like the one included in eslint-plugin-deprecation with support for ESLint v9, you can also consider switching to the typescript-eslint rule @typescript-eslint/no-deprecated, which was released recently in [email protected]:

• Docs: https://typescript-eslint.io/rules/no-deprecated/
• Issue: Rule proposal: Warn when deprecated APIs are used (eslint-plugin-deprecation) typescript-eslint/typescript-eslint#8988
• PR: feat(eslint-plugin): [no-deprecated] add rule typescript-eslint/typescript-eslint#9783

Diff:

-import deprecation from 'eslint-plugin-deprecation';

// ...

    plugins: {
      'eslint-comments': eslintComments,
-     deprecation: fixupPluginRules(
-       /** @type {import("eslint").ESLint.Plugin} */ (
-         /** @type {unknown} */ (deprecation)
-       ),
-     ),
    },

// ...

    rules: {
-     // Warn about usage of deprecated APIs
-     // https://github.com/gund/eslint-plugin-deprecation
-     'deprecation/deprecation': 'warn',
+     // Warn about usage of deprecated APIs
+     // https://typescript-eslint.io/rules/no-deprecated/
+     '@typescript-eslint/no-deprecated': 'warn',

Caveat: In my first testing, it felt like it may be slower than eslint-plugin-deprecation.

[SimonSchick]

This resolves this for us, ty.