Cabal Dir Environment variable added

[kwrooijen]

I adjusted the defaultCabalDir function so that if you have CABAL_DIR environment variable it will default to that location instead of $HOME/.cabal

[tibbe]

If I'm allowed to bikeshed a bit I think these kind of variables are usually called <binary>_HOME, as in JAVA_HOME, SCALA_HOME, PYTHONHOME.

[dcoutts]

Can someone comment on why this is needed? It seems to duplicate the existing env var to specify which ~/.cabal/config file to read.

Perhaps what we need is the ability to have dirs in the ~/.cabal/config file that are relative to its location, so you can use the same file and relocate it without changing anything.

[sajith]

Here is one use cases I can think of:

At the university we have everyone's home directories mounted on NFS. And the machines are a mix of i686 and x86-64. (If this was 1995 there would be Alphas and SGIs and SPARCs...) I'm not sure this is a thing, but it would be ideal if Cabal is aware of architectures and could let people install packages for different architectures side-by-side. (GHC seems to have some notion of machine type-compiler version, so why not Cabal?)

(I'm fairly clueless and I'm not sure there's an existing elegant way to solve this. I found this thread when looking for a way to run Xmonad on the above-stated i686 machines.)

[23Skidoo]

@sajith I think your problem was fixed by recent cross-compiling-related changes (packages are now installed under $arch-$os-$compiler/$pkgid instead of $pkgid/$compiler).

[23Skidoo]

@dcoutts

Perhaps what we need is the ability to have dirs in the ~/.cabal/config file that are relative to its location, so you can use the same file and relocate it without changing anything.

What if instead of adding $CABAL_HOME we did something like this:

defaultCabalDir :: IO FilePath
defaultCabalDir = do
  mEnv <- lookupEnv "CABAL_CONFIG"
  maybe (getAppUserDataDirectory "cabal") (fmap takeDirectory . canonicalizePath) mEnv

?

[dcoutts]

Or perhaps we just need a general "where cabal puts its misc other files" entry in the config. And we'd use that for the things that don't have another specific entry in the ~/.cabal/config.

Indeed we could remove some of the other config entries like world-file and just make them relative to this "general cabal files" setting.

[23Skidoo]

Closing in favor of #1242.

[mietek]

This enhancement would have been appreciated.