Hi Maxim,
I was aware of this hackish vim-script. I even tried to use that but fell into lots of corner cases and dropped. It does not handle inter-package dependencies, haskell language extensions, different code or sandbox layout.
It's definitively nice to reuse the information of the cabal file, I just don't like the coupling of tools that much. Also there seems to be duplicate effort for supporting cabal sandboxes in ghc-mod and hdevtools. It would be nice to have a tool that extracts the ghc relevant options from the cabal file which then could be used by ghc-mod, hdevtools or any other tool that wants to use ghc in conjunction with cabal. Getting the ghc options right you also have to use the right cabal section (which executable, library, which test suite ...), so a seperate tool could nicely support this. Greetings, Daniel