renovate-config-validator gives wrong validation result when re2 is not available

[silverwind]

How are you running Renovate?

pnpm dlx --package renovate renovate-config-validator — --package renovate

Which platform you running Renovate on?

GitHub.com

Which version of Renovate are you using?

43.281.1

Please tell us more about your question or problem

When re2 is not available, for example currently with Node.js 26 on MacOS where no pre-built binary exists, renovate-config-validator silently falls back to the JS regex engine which yields incorrect validation results when regexes contain features not supported by re2, like lookahead.

Would suggest to either hard-fail config validation when re2 is unavailable or at least output a warning that regex validation may not be accurate.

Related bug: go-gitea/gitea#38656

Logs (if relevant)

No response

[RahulGautamSingh]

Agreed a silent fallback here is misleading. A warning (or hard-fail) when re2 is unavailable makes sense so users know validation accuracy can't be guaranteed. PR welcome, thanks!