Override src of an Haskell package

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1

Hi,

hledger is defined in /pkgs/development/haskell-modules/hackage-packages.nix. I would like that Nix use the hledger git repository that I cloned on my home directory so it contains my experimental patches.

How can I override the source of an hackage package in Nix?

Thanks

1 Like
2

There’s a good chance that the end result is still a normal derivation created with mkDerivation. If so, you should be able to use overrideAttrs:

environment.systemPackages = with pkgs; [
  ...
  (pkgs.hledger.overrideAttrs (oldAttrs: rec {
    src = ...l
   }))
]
3 Likes
3

overrideAttrs does not work for haskellPackages as far as I know. There is however an easy to use alternative:

environment.systemPackages = with pkgs; [
  ...
  (pkgs.haskell.lib.overrideSrc pkgs.hledger {
    src = /path/to/your/repository;
    version = "unstable";
  })
  ...
]

You could also alternatively define an overlay so the hledger package is changed in pkgs:

let
  hledger-dev-overlay = self: super: {
    hledger = self.haskell.lib.overrideSrc super.hledger {
      version = "unstable";
      src = /path/to/git/repo;
    };
  };
in
...

If you want haskellPackages that depend on hledger to use the development version as well, you may need to use haskellPackages.haskellPackages.override.

4

Thank you @emmanuelrosa and @sternenseemann for your help. Unfortunately, both solutions result in the same error:

Setup: No cabal file found. Please create a package description file .cabal

5

The hledger repository contains multiple subdirectories for the individual packages, probably you specified the root directory which contains no .cabal file.

1 Like
6

Thank you for your answer. Specifying the hdleger/ sub directory (which is the CLI executable I need) doesn’t work either because it depends on the sibling directory hledger-lib.

1 Like
7

Sorry for the late answer.

I guess the error is a version constraint failure? I think in that case it should be enough to override the hledger-lib attribute in haskellPackages as well. I’m pretty sure the hledger package does not need to access that directory, just depends on the package which is in the other directory.

Side note: Hledger uses hpack which can catch you out when the cabal and package.yaml files are not syncronized with each other. cabal2nix has support for hpack, so I’m not sure if the package.yaml or hledger.cabal file are used as a base in that case.