Hello, I’ve investigated an issue (#9176) where ghc with --make -dynamic-too appears to run successfully but doesn’t generate some .dyn_hi files. The cause seems to be that GHC silently turns off dynamic-too output when it finds an inconsistency between the .hi and .dyn_hi interface hashes of an imported module. The symptom, for me, is that some cabal packages will build but fail to install. The real problem is most likely not in the failing package, but in an imported module from a package that’s already installed. I’m inclined to say that GHC should stop with an error in this situation, which would produce a visible error when the file fails to compile. However, since GHC carefully avoids bailing out, I wonder if I’m missing something. Is there a good reason to turn off dynamic-too output instead of reporting an error? Additionally, is it ever valid to have a pair of .hi and .dyn_hi files with different interface hashes? Or is it invalid data, in the same way that a corrupted .hi file is invalid data? I’m inclined to say that it is invalid data, because -dynamic-too promises to generate two different (static and dynamic) implementations of the same Haskell code, taking two different implementations of the same imported Haskell modules as input. If the inputs aren’t really two different implementations of the same Haskell code, you’ve somehow provided invalid input.