Descriptive error messages in checkEnabled(OneOf).

I have enabled stylish-haskell in my IntelliJ and was greeted with this error message.
Initially I thought I had to enable some sort of stylish-haskell plugin and started googling for a solution.
Only after trying another time on a different file, I realised it was about a language pragma missing:
the second file was missing a pragma which I recognised the name of (the first one I didn't know).
Only then did I realise that it is not stylish-haskell that is complaining, but this code.