The work we do when producing diagnostics sometimes has side effects, like pushing things into caches, which can affect other calculations down the line, so I'm usually wary against produceDiagnostics checks that aren't immediately around an error call, as it can the a source of reeeeeaaally hard to track bugs where hover info and error info on a symbol don't match (hover data comes from a non-diagnostics producing checkers, while errors do). Specifically here, there's a nested conditional checkResolvedBlockScopedVariable that might toss something into a cache which now we'd avoid doing - it's probably fine until proven otherwise, since everything in the guarded branch is supposed to just be to generate an error message, I'd just keep it in mind in case something weird crops up in the future.