Hi Ryan,
Some preogress... The cabal issues I reported seem more of a nix issue but I'm not sure what is causing them. FWIW, nix does not use cabal-install at all but instead compiles the Setup.hs script and runs that.
The weird thing is that i'm trying to reproduce what the nix haskell-package builder [1] does and the problem I described (no Main.hs could be found) does not occur but instead the Main.hs module fails to compile due to an unrelated error. So it seems that, somehow, the unrelated compile error is being mistaken by a lack of module.
Even weirder is that the snap-server.cabal says that the failing executables should only be built when flags are enabled (which are disabled by default) but they are being built anyway when nix calls Setup, even when I explicitly disable them via nix. The nix build log [2] even says that the flags (build-pong and build-testserver) are disabled! However, If I manually execute Setup the configure flags are honored.
I'll continue to investigate to try and make some sense of this but I think it's not cabal's fault so feel free to ignore me for the meantime. I'll chime back if/when I find it is an issue with the new Cabal.
Thanks,
Alberto