Better way to use nixpkgs git repo

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1

Hello! I have a question about better usage of nixpkgs github repo. For example I want to use this expression

Atm I have nixpkgs as submodule in git repo of my library. So far it was ok to have it, but I found that if I’m using my library in other haskell stack project (as extra-dep), stack build tool tries to fetch all library submodules with the command

git submodule update --init --recursive

Which is ok, but not for this huge repo. And I don’t see possibility to say stack to add --depth 1 parameter or something like that. So maybe there are better ways to use nixpkgs than just git submodule in project? Thanks!

2

i think what you are trying to accomplish can be done like so:

src = fetchgit {
    url = "https://github.com/your_repo/with_submodules.git";
    rev = "...";
    sha256 = "...";
    deepClone = false;
    fetchSubmodules = false;
  };
3

Haskell stack don’t understand nix expressions. In my case it has library with submodules in stack.yaml

extra-deps:
       - github: organization/package
         commit: ...

where organization/package has nixpkgs as submodule. I’m thinking how to avoid usage of nixpkgs submodule, because tools like haskell stack are doing only deep clone.

4

I’m just thinking that my approach to have access to nixpkgs expressions through git submodule might be wrong. I’m just not aware of alternatives.

5

Using builtins.fetchTarball you can avoid git cloning nixpkgs.git. Create a nixpkgs.nix containing this for instance:

builtins.fetchTarball {url="https://github.com/NixOS/nixpkgs-channels/archive/b7bdf48e3fa6b90ea475a03ed159f397bd3c3c65.tar.gz"; sha256="0ap49yync5rwvr5qn0qb45x2yzzix2vhfqfljbampdhs0ncnhigi";}

and use it in a shell.nix like this:

let
  nixpkgs = import ./nixpkgs.nix;
  pkgs = import nixpkgs {};
in
pkgs.mkShell {
  buildInputs = [
    pkgs.stack
  ];
  shellHook = ''
    export NIX_PATH="nixpkgs=${nixpkgs}"
  '';
}

You can generate this nixpkgs.nix like that (eg. in a .envrc when nixpkgs.nix does not exist):

nixpkgs_channel=nixos-unstable-small
rev=$(curl -L https://nixos.org/channels/"$nixpkgs_channel"/git-revision | head -n1 | tr -dC 'a-z0-9')             sha256=$(nix-prefetch-url --unpack https://github.com/NixOS/nixpkgs-channels/archive/"$rev".tar.gz)
echo >nixpkgs.nix "builtins.fetchTarball {url=\"https://github.com/NixOS/nixpkgs-channels/archive/$rev.tar.gz\"; sha256=\"$sha256\";}"

If you need to patch nixpkgs (when overlays are not powerful enough, eg. to change the type of an option of a NixOS service, or to directly fetch a PR which is not merged yet), you can do like this:

let
  originNixpkgs = import ./nixpkgs.nix;
  originPkgs = import originNixpkgs {};
  nixpkgsPatches = [
    { meta.description = "Dovecot plugin for Full Text Search (FTS) with Xapian";
      url = "https://github.com/NixOS/nixpkgs/pull/78780.diff";
      sha256 = "053md69ryybj27cp0xdfrza48zyzpblk6wvb2m2dbs9hm0gmcwc4";
    }
    { meta.description = "dstat: fix pluginpath";
      url = "https://github.com/NixOS/nixpkgs/pull/80151.diff";
      sha256 = "0jjw2gvp7b7v2n2m2d6yj0gw711j6p9lyjf5ywp2y9ql6905qf4b";
    }
  ];
  localNixpkgsPatches = [
    #patches/direnv.diff
  ];
  nixpkgs = originPkgs.stdenv.mkDerivation {
    name = "nixpkgs-patched";
    src = originNixpkgs;
    phases = [ "unpackPhase" "patchPhase" ];
    patches = map originPkgs.fetchpatch nixpkgsPatches ++ localNixpkgsPatches;
    postPatch = ''
      patch=$(printf '%s\n' ${builtins.concatStringsSep " " (map (p: p.sha256) nixpkgsPatches)} |
        sort | sha256sum | cut -c -7)
      mv $PWD $out
      echo "+patch-$patch" >$out/.version-suffix
    '';
  };
  pkgs = import nixpkgs {
    config = {}; # Make the config pure, ignoring user's config.
    #overlays = import ./overlays.nix;
  };
in
[...]

HTH,
Julien

2 Likes
7

Thanks! But it’s still unclear for me how exactly I can access this expression

Now when I have submodule, I’m just using

import ./nixpkgs/pkgs/development/beam-modules/build-mix.nix {
               inherit stdenv writeText elixir erlang hex lib;
             }
8

Importing yourself a path from within nixpkgs is rarely needed, I guess here you could use pkgs.beamPackages.hex.

Should you want to do such a contrived import, here is how you can:

nix-instantiate --eval --expr 'let nixpkgs = import ./nixpkgs.nix; pkgs = import nixpkgs {}; hex = pkgs.callPackage (nixpkgs + "/pkgs/development/beam-modules/hex") {}; in hex'

Or using the nixpkgs in your $NIX_PATH:

nix-instantiate --eval --expr 'let pkgs = import <nixpkgs> {}; hex = pkgs.callPackage <nixpkgs/pkgs/development/beam-modules/hex> {}; in hex'

Here, using pkgs.callPackage is like your import but avoids the manual inherit by auto-supplying attributes using those in pkgs.
You can override those using the extra {} if need be.

1 Like
9

Wow, that implicit inherit looks cool, I’ll definitely try it out, thanks!