The current tooling works well if all of your dependencies can be compiled with the versions of packages specified on stackage. But if some of them don’t (for example if the versions are too new), it can go horribly wrong. You’ll need to manually pick specific versions of packages, and override them in the package set, similar to what you’d usually do in stack.yaml. This process is tedious, error-prone, and needs to be done every time nixpkgs updates. This is also what a dependency solver is for. I think we definitely need something that can take advantage of cabal’s solver to help us generate a build plan. Currently only haskell.nix can do this and I think nixpkgs definitely need this as well.
This issue has been addressed in greater detail in my preview post: A summary of the problems I met while using the current nixpkgs Haskell infrastructure (And my thoughts on how to solve them).