Developer finds 140 deprecated API calls in own ESLint plugins before ESLint 10 launch

A self-audit of 20 ESLint plugins revealed 140 files still using three API methods — getFilename(), getSourceCode(), and getCwd() — that ESLint 10 will remove entirely, not just deprecate. The issue went undetected on ESLint 9 because compatibility shims kept the calls functional, meaning the breakage would only surface on ESLint 10 despite README claims of full version support. A separate plugin, eslint-plugin-security, was found to crash outright on ESLint 9 flat config, illustrating that a passing quality score can coexist with a real runtime failure. The developer maintains 23 benchmark suites across two public stacks, but acknowledges only one of four serverless benchmark suites currently has complete, verified numbers. The central argument is that version-compatibility testing via matrix runs — not aggregate quality scores — is the only reliable way to validate multi-version support claims.