I was under the impression (but could be mistaken) that Cabal doesn't show warnings while building dependencies.

I don't remember, either, and it depends on commandline options, but I think it does show the full log at least when a dependency fails to compile.

Not that I could find. I should work on a minimal reproducible test- case and file something.

Yes, thank you, please do.

- Keep warnings in package.cabal ghc-options/cc-options etc - Add -Werror in cabal.project so things fail on dev machines - Configure HaskellCI to have -Werror as well, given a no-warnings policy

Brutal but effective. :)