Ideally we’d have a way to parse and validate separate regexps from individual patterns (reporting errors with only the relevant line), then combine them (like in https://twitter.com/thingskatedid/status/1472360823058157569 and the preceding thread). If it’s cheap to combine already-fully-compiled DFAs, maybe the regex crate could have an API that takes multiple Regex values? In the meantime if we accept some duplicated setup-time work we could validate each pattern with Regex::new, report errors individually, throw away successful results and then at the end build the mega-regex from concatenated strings like now.

The second option was my idea, I don't know how much churn that would imply, but I feel like it would make the debugging experience much better.