Skip to content
master
Switch branches/tags
Code

Latest commit

 

Git stats

Files

Permalink
Failed to load latest commit information.
Type
Name
Latest commit message
Commit time
 
 
doc
 
 
 
 
src
 
 
 
 
 
 
 
 
 
 
 
 
 
 

Cabal2nix

hackage release stackage LTS package stackage Nightly package Continous Integration

cabal2nix converts a single Cabal file into a single Nix build expression. For example:

$ cabal2nix cabal://mtl
{ mkDerivation, base, lib, transformers }:
mkDerivation {
  pname = "mtl";
  version = "2.2.1";
  sha256 = "1icdbj2rshzn0m1zz5wa7v3xvkf6qw811p4s7jgqwvx1ydwrvrfa";
  libraryHaskellDepends = [ base transformers ];
  homepage = "http://github.com/ekmett/mtl";
  description = "Monad classes, using functional dependencies";
  license = lib.licenses.bsd3;
}

Cabal files can be referred to using the magic URL cabal://NAME-VERSION, which will automatically download the file from Hackage. Alternatively, a direct http://host/path/pkg.cabal URL can be provided, as well as a file:///local/path/pkg.cabal URI that doesn't depend on network access. However, if the source hash is not already in cabal2nix's cache or provided using the --sha256 option, cabal2nix still needs to download the source code to compute the hash, which still causes network traffic. Run the utility with --help to see the complete list of supported command-line flags.

Detailed instructions on how to use those generated files with Nix can be found at https://haskell4nix.readthedocs.io/nixpkgs-users-guide.html#how-to-create-nix-builds-for-your-own-private-haskell-packages.

cabal2nix can also build derivations for projects from other sources than Hackage. You only need to provide a URI that points to a cabal project. The most common use-case for this is probably to generate a derivation for a project on the local file system:

$ cabal get mtl-2.2.1 && cd mtl-2.2.1
$ cabal2nix .
{ mkDerivation, base, lib, transformers }:
mkDerivation {
  pname = "mtl";
  version = "2.2.1";
  src = ./.;
  libraryHaskellDepends = [ base transformers ];
  homepage = "http://github.com/ekmett/mtl";
  description = "Monad classes, using functional dependencies";
  license = lib.licenses.bsd3;
}

This derivation will not fetch from hackage, but instead use the directory which contains the derivation as the source repository.

cabal2nix currently supports the following repository types:

  • directory
  • source archive (zip, tar.gz, ...) from http or https URL or local file.
  • git, mercurial, svn or bazaar repository

hackage2nix

This repository also contains, in the hackage2nix/ directory, the tool to update the Haskell packages in nixpkgs. It has its own README there.

Building

cabal2nix is built using cabal-install, like you'd expect, and you are free to use your favourite way of setting up a Haskell development environment.

Since cabal2nix is quite intertwined with the packages distribution-nixpkgs and hackage-db, we recommend setting up a shared development environment for the three packages like so:

$ mkdir /path/to/cabal2nix-root && cd /path/to/cabal2nix-root
$ # clone repositories, note that you may need to checkout an
$ # older tag for some depending on breaking changes on master.
$ git clone https://github.com/NixOS/cabal2nix.git
$ git clone https://github.com/NixOS/hackage-db.git
$ git clone https://github.com/NixOS/distribution-nixpkgs.git
$ # setup development environment with shellFor
$ cat > shell.nix << EOF
# assumes nix{os,pkgs}-unstable
{ pkgs ? import <nixpkgs> {} }:

pkgs.haskellPackages.shellFor {
  packages = p: [
    p.cabal2nix-unstable
    p.distribution-nixpkgs
    p.hackage-db
  ];

  # for running doctests locally
  nativeBuildInputs = [
    pkgs.haskellPackages.doctest
  ];

  # set environment variable, so the development version of
  # distribution-nixpkgs finds derivation-attr-paths.nix
  distribution_nixpkgs_datadir = toString ./distribution-nixpkgs;
}
EOF
$ # tell cabal about local packages
$ cat > cabal.project << EOF
packages: ./*/*.cabal
EOF
$ # test our new development environment
$ nix-shell --run "cabal v2-build exe:cabal2nix exe:hackage2nix"