Stacklock2nix: easily build Stack-based Haskell projects with Nix

cdepillabout · January 13, 2023, 11:53am

A few weeks ago I put together a Nix library stacklock2nix. It enables you to easily build a Stack-based Haskell project with the Haskell infrastructure from Nixpkgs:

stacklock2nix is an alternative to haskell.nix for projects that:

you want to build with the Haskell infrastructure in Nixpkgs
you already have a stack.yaml.lock file, and want to generate a package set with package versions based off the stack.yaml.lock
you don’t need all the functionality provided by haskell.nix

I’m using stacklock2nix to build a sizeable Haskell project at work, and it seems to be working relatively smoothly. I’ve also written a series of blog posts about packaging various Haskell projects using stacklock2nix. Each blog post contains some example code using stacklock2nix:

The stacklock2nix repo also has an example Haskell project that can build with stacklock2nix. Here’s a flake.nix from that project that you can use to get an idea of stacklock2nix:

github.com

cdepillabout/stacklock2nix/blob/ebe40119dea257906044ecb1543c44ca57748764/my-example-haskell-lib-easy/flake.nix#L39-L105

    
      
          # This is a top-level attribute that contains the result from calling
          # stacklock2nix.
          my-example-haskell-stacklock = final.stacklock2nix {
            stackYaml = ./stack.yaml;
          
          
  # The Haskell package set to use as a base.  You should change this
            # based on the compiler version from the resolver in your stack.yaml.
            baseHaskellPkgSet = final.haskell.packages.ghc924;
          
          
  # Any additional Haskell package overrides you may want to add.
            additionalHaskellPkgSetOverrides = hfinal: hprev: {
              # The servant-cassava.cabal file is malformed on GitHub:
              # https://github.com/haskell-servant/servant-cassava/pull/29
              servant-cassava =
                final.haskell.lib.compose.overrideCabal
                  { editedCabalFile = null; revision = null; }
                  hprev.servant-cassava;
            };
          
          
  # Additional packages that should be available for development.

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Additional documentation can be found in the stacklock2nix README.

I also posted about stacklock2nix on the NixOS Discourse, and there was some interesting discussion there.