I've started looking at this. Part of the problem is that nix wants (reasonably) to do "everything itself", including (for example) bundling the OS X SDKs itself.
At the moment that's broken (the 10.9 SDK is installed in 10.11, then links against some 10.11 libraries, which is blocking mplayer). I don't have the knowledge to fix it.
homebrew and fink have had the same problem (deciding when to link against system libraries and when to try to rebuild) -- hopefully nix will get over this hurdle.
The correct answer for Nix is to never link against a library provided by the system. Nix provides its own bootstrap binaries and it must be done that way for the sake of reproducibility.
well, there's xcode-select to chose the SDK you want which kinda implies the availability of multiple – currently for example swift 2.2 and 3.0.
I'm tempted by the "1-environment" idea but homebrew has done such an excellent job in comparison to fink/port, I';; stay loyal. Also wondering if those two projects couldn't profit from some code sharing?
Out of interest, how'd you get your OS X builds set up? I had to do quite a lot of searching before I found a company [2] willing to lend PureDarwin [1] a box for a while.
At the moment that's broken (the 10.9 SDK is installed in 10.11, then links against some 10.11 libraries, which is blocking mplayer). I don't have the knowledge to fix it.
homebrew and fink have had the same problem (deciding when to link against system libraries and when to try to rebuild) -- hopefully nix will get over this hurdle.