chore: remove ESLint compatibility code

[9romise]

Since our minimum supported version is currently ESLint 8.57.0.

This PR aligns with the migration guide at https://eslint.org/blog/2023/09/preparing-custom-rules-eslint-v9/, replacing certain APIs that will be removed in ESLint v10 with their modern equivalents.

Related:

• https://eslint.org/blog/2023/09/preparing-custom-rules-eslint-v9/
• https://eslint.org/blog/2025/10/whats-coming-in-eslint-10.0.0/

[changeset-bot]

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Latest commit: 9adaecf

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[FloEdelmann]

I'm sorry @9romise, I pushed some changes that failed the tests. After reverting and even force-pushing to remove the commit, now the tests even fail for your last commit, where they previously passed. I guess something's in the cache somewhere that shouldn't be there.

Regarding your changes, those look good to me. Thank you for cleaning up! 🙂

[Copilot]

Pull request overview

This PR removes ESLint compatibility code for older versions (< 8.57.0) and migrates to modern ESLint v9/v10 APIs. Since the minimum supported ESLint version is now 8.57.0, the code no longer needs to maintain backward-compatible wrappers for deprecated APIs.

• Updated TypeScript definitions to reflect required vs optional context properties
• Replaced deprecated method calls (getSourceCode(), getFilename(), getCwd()) with direct property access (sourceCode, filename, cwd)
• Removed the markVariableAsUsed utility wrapper function since context.sourceCode.markVariableAsUsed is now always available

Reviewed changes

Copilot reviewed 101 out of 102 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
typings/eslint/index.d.ts	Updated type definitions to mark deprecated methods as optional and new properties as required; clarified ESLint v10 deprecation comments
lib/utils/index.js	Removed markVariableAsUsed utility wrapper and simplified getDeclaredVariables implementation; updated all getSourceCode() calls to sourceCode property
lib/rules/*.js	Replaced deprecated method calls with direct property access across all rule files
tests/lib/utils/selector.js	Updated test utility to use context.sourceCode directly
lib/utils/*.js	Updated utility functions to use modern context properties

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[ota-meshi]

LGTM! Thank you!
The CI error should be fixed in #2969.