Group package set related options

[srid]

Detached from #52 (comment)

haskellProjects.foo = {
  devShell.enable = false;
  packageSet = {
    # The overlays are composed in the order they are shown here.
    base = pkgs.haskell.packages.ghc944;
    local = {
      mypkg.root = ./.;  # Assumes mypkg.cabal
    };
    source-overrides = { .. }; # Overrides by direct path to source
    overrides = self: super:  { .. };  # Raw Haskell overlay
  };
};

Users can then use config.haskellPackages.foo.packageSet.final to access all the packages. The idea is that we can say "start from base", then we apply local, then source-overrides and finally overrides, before creating the project specific haskell package set.

finalPackages of #68 would become packageSet.final.

[roberth]

I'm not convinced yet, because it makes the syntax a little bit more complicated. I think of a haskellProject as a package set, and if I need more than one package set, I need to use multiple projects anyway.

We don't have a module for warnings / assertions support yet, but that could be added in flake-parts.

[srid]

because it makes the syntax a little bit more complicated. I think of a haskellProject as a package set, and if I need more than one package set, I need to use multiple projects anyway.

That's fair.