haskell.nix/docs/user-guide-cabal.md

User Guide (cabal project)

Here we will look into how to generate the pkgs.nix file for a cabal.project project. For the full integration please see the User Guide

Using plan-to-nix

We currently don't have a project-to-nix tool yet, as such creating the relevant pkgs.nix file for a cabal.project is slightly more involved than for a corresponding stack project.

With nix-tools in PATH, we can simply run the following command on a cabal package:

# make sure the cabal project is configured (the plan.json file is generated)
cabal new-configure
# convert the plan.json file into a pkgs.nix file
plan-to-nix dist-newstyle/cache/plan.json > nix/plan.nix

This will produce a nix/plan.nix file that looks like the following:

hackage:
  {
    packages = {
      "o-clock" = hackage.o-clock."0.1.1".revisions.default;
      ...
    };
    compiler = { ... };
  }

it specifically does not include any of our local packages yet. We will need to run

cabal-to-nix $path > nix/$pkg.nix

or

cabal-to-nix $url $rev > nix/$pkg.nix

for each local (or source) package.

With this in place we can then proceed to build the nix/pkgs.nix file as follows:

let plan = import ./plan.nix; in
{ pkg-def = plan;
  extras =
    { local-package-a = ./local-package-a.nix;
      local-package-b = ./local-package-b.nix;
      source-import-a = ./source-import-a.nix;
      source-import-b = ./source-import-b.nix;
      ...
    };
}

If you came here from the User Guide, go back and complete the setup.