fix: add ESLint 10 compatibility by replacing deprecated context.getSourceCode()

[aklkv]

Summary

Adds ESLint 10 compatibility by replacing the deprecated context.getSourceCode() API with the backward-compatible pattern context.sourceCode ?? context.getSourceCode().

Fixes #2378

Changes

• Updated 60 occurrences of context.getSourceCode() across 35 files to use the backward-compatible pattern
• Added CI job to test against ESLint 8, 9, and 10

Details

ESLint 10 removed the deprecated context.getSourceCode() method. The new pattern works with ESLint 8, 9, and 10:

// Before
const sourceCode = context.getSourceCode();

// After
const sourceCode = context.sourceCode ?? context.getSourceCode();

[NullVoxPopuli]

The eslint matrix failed. Tyty for doing this!

[aklkv]

I will circle back to it once typescript-eslint/typescript-eslint#11952 is resolved as it doesn't even seem to be feasible to upgrade just yet

[saracope]

@aklkv This one is blocking me to. Is it able to move forward?

[aklkv]

@saracope I will check situation upstream

[aklkv]

ESLint 10 Compatibility Update

Summary

Added ESLint 10 compatibility layer to the test infrastructure and updated rules to handle API changes.

Changes Made

1. Updated 18 rule files to use context.filename ?? context.getFilename() pattern (ESLint 10 removed context.getFilename())
2. Enhanced tests/helpers/eslint-compat.js with:
   • ESLint 10 detection (isESLint10OrLater)
   • Error property normalization (ESLint 10 only allows specific error properties)
   • Valid test case output property stripping (disallowed in ESLint 10)

Test Results

ESLint Version	Status	Tests
ESLint 8	✅ Pass	3868/3868
ESLint 9	✅ Pass	3868/3868
ESLint 10	⚠️ Blocked	1846/3868

ESLint 10 Blocker

The remaining ESLint 10 failures are caused by @babel/eslint-parser@7 using scopeManager.addGlobals() which was removed in ESLint 10. This is an upstream dependency issue.

With @babel/[email protected]: 3808/3841 tests pass (33 failures are autofix whitespace differences, not rule logic issues).

However, Babel 8 requires ESLint ≥9 as a peer dependency, so we can't use it without dropping ESLint 8 support.

Related Babel Issues/PRs

Issue	Status	Notes
#17791 - babel/eslint parser failing with ESLint 10	Closed	Closed 2 weeks ago
#17804 - @babel/eslint-parser incompatible with ESLint 10	Duplicate	Marked as duplicate, closed 2 weeks ago
#17821 - [@babel/[email protected]] Broken Types	Open	Type issues with Babel 8 rc2
#17819 - Bump @eslint/js to 10.0.1	Merged	ESLint 10 support merged 2 weeks ago

Next Steps

• Wait for @babel/eslint-parser stable Babel 8 release (ESLint 10 support has been merged)
• Alternatively, drop ESLint 8 support and upgrade to Babel 8 rc2 now

@NullVoxPopuli thoughts?

[NullVoxPopuli]

Wait for @babel/eslint-parser stable Babel 8 release (ESLint 10 support has been merged)

we can widen the range on @babel/eslint-parser and test against both supportetd and upcoming.

as in -- when testing eslint 10, we should also use @babel/eslint-parser 8

[NullVoxPopuli]

I wonder if it better to specify decorator-transforms here?

these babel plugins are generally considered bad for the legacy transform 🤔

[aklkv]

updated