According to <http://hackage.haskell.org/trac/ghc/ticket/4013>, this
feature won't work with XCode versions older than 3.2.
This means that Mac users will have considerably larger binaries because
some build-time dependencies (such as HTTP) will be mis-detected as
run-time dependencies.
This patch configures all Cabal builds with '--enable-split-objs' unless the
Nix expression explicitly sets "enableSplitObjs = false". The Cabal manual [1]
describes this option as follows:
| The GHC -split-objs reduces the final size of the executables that use the
| library by allowing them to link with only the bits that they use rather
| than the entire library. The downside is that building the library takes
| longer and uses considerably more memory.
One immediate benefit of this change is that the 'darcs' closure defined in the
top-level no longer refers to GHC. The same is probably true with other
executable packages.
[1] http://www.haskell.org/cabal/users-guide/installing-packages.html#setup-configure
Jailbreaks-cabal allows Nixpkgs maintainers to quick-fix builds of packages
that over-specify their version requirements by removing the version
restrictions of all dependencies from the Cabal file. Set
jailbreak = true
in the build expression to activate this feature.
