The cabal2nix monorepo

Components

cabal2nix

Tool that generates Nix build instructions from a Cabal file. Also contains hackage2nix, the tool that generates the haskellPackages set in nixpkgs.

distribution-nixpkgs

Utility library implementing nixpkgs-specific tasks and concepts: Looking up packages, meta sets, Nix-style integrity hashes etc.

language-nix

Simplistic library to parse and render a subset of the Nix language.

hackage-db

Library for working with the Hackage database created and updated using cabal update.

Development

At the top-level, a cabal.project and shell.nix are provided for working on all packages in the repository. You can use direnv and (optionally) lorri to make the environment available in your normal shell as well.

Maintenance

The monorepo has been assembled using josh. You can obtain it from nixpkgs using nix-shell -p josh. Below, some common tasks are documented.

Extracting the original git history

josh's history filtering capabilities are quite powerful, allowing us to extract the original git histories of the repositories that have been vendored in. For example, for distribution-nixpkgs:

$ josh-filter ':/distribution-nixpkgs'
$ git checkout FILTERED_HEAD
$ ls *.cabal
distribution-nixpkgs.cabal

The FILTERED_HEAD ref has the original HEAD of the distribution-nixpkgs HEAD when it was vendored as its ancestor and can thus be pushed to the original repository.

Vendoring components

This probably won't come up in the future, but the process that was used to vendor the additional libraries is documented here:

$ name=…
$ git fetch https://github.com/nixos/$name.git
$ josh-filter ":prefix=$name" FETCH_HEAD
$ git merge --allow-unrelated-histories FILTERED_HEAD -m "$name: subtree upstream repo"

Also refer to the relevant josh documentation.