Since the Guix folks are on the record above, I’ll just say that this is exactly the goal of Spack (GitHub - spack/spack: A flexible package manager that supports multiple versions, configurations, platforms, and compilers.), but not just for versions. Spack is heavily inspired by Nix, but it’s more of a departure from Nix than Guix. Recipes are templated by version, compiler, build target, and arbitrary other parameters (“variants”) that can be exposed by the package.
$ spack install mpileaks # unconstrained
$ spack install mpileaks@3.3 # @ custom version
$ spack install mpileaks@3.3 %gcc@4.7.3 # % custom compiler
$ spack install mpileaks@3.3 %gcc@4.7.3 +threads # +/- build option
$ spack install mpileaks@3.3 cppflags="-O3 –g3" # custom compiler flags
$ spack install mpileaks@3.3 target=skylake # set target microarchitecture
$ spack install mpileaks@3.3 ^mpich@3.2 %gcc@4.9.3 # ^ dependency information
There’s no external database here, though – the packages expose options and constraints that define the space of possible builds, and we resolve a DAG from that. Spack allows you to have multiple environments with arbitrary configurations in them much like Nix, but it’s parameterized. We have to make some tradeoffs to allow that.
The builds are “reproducible” in the sense that the packages files + the concrete (resolved) DAG description with all the metadata will result in the same build. We don’t guarantee that spack install foo@version will always do the same thing, but we generate a lockfile that you can reproduce a particular configuration from. So it’s similar to what Nix in some ways, but you have to do dependency resolution to allow arbitrary parameters like this. If you are interested in this, see this FOSDEM talk.
I think the Nix folks will have disagreements about some of the things we did in Spack to allow this flexibility, so I’ll be interested to see how this discussion plays out and how people might do this in Nix. I’d be interested to know if Spack fits your use case, as well as what from Nix is lacking that you’d miss (I’m sure there are plenty of things – Spack is not as mature as Nix yet!)