Я нашел вот это rebuild-ghc-options
Should we rebuild a package when its GHC options change? Before 0.1.6, this was a non-configurable true. However, in most cases, the flag is used to affect optimization levels and warning behavior, for which GHC itself doesn't actually recompile the modules anyway. Therefore, the new behavior is to not recompile on an options change
Интересно, почему они говорят, что в таком случае GHC не перекомпилирует модули на самом деле