@Ericson2314 what do you think? Plausible?

Err these are runtime dependencies of cabal2nix, right? If so, I don't think this is the right approach. My guess is that there is a patchShebangs messing up the prefetch script build, and I think @dtzWill recently fixed something with the Nix cross compile but maybe did so on staging.

When would I want to use the them not from the buildPackages? After all nix is run on the build machine, no?

After all nix is run on the build machine, no?

Ahhh. Yeah never think about where the current package will be used, because assumptions on the downstream will cripple composition. Instead, since cabal2nix depends on nix at run time, cabal2nix and cabal2nix's nix must come from the same bootstrapping stage. If we are doing a callCabal2nix on the current machine, yes cabal2nix and nix would come from buildPackages and run on the build machine. But if we are cross-compiling an entirely NixOS with cabal2nix pre-installed globally, both come from pkgs as both will run on the host machine.

In short, buildPackages.cabal2nix -> buildPackages.nix, pkgs.cabal2nix -> pkgs.nix, targetPackages.cabal2nix -> pkgs.nix.