[Nix-dev] Haskell dependencies in a project

[Tomasz Czyż]

Hi,

I'm trying to make a nix/haskell package (with executable) with some
dependencies (from nixpkgs and some locally declared).

I have my-dep directory with haskell package exposing library and src
directory which contains application using my-dep dependency and aeson
package from nixpkgs.

Here is my nix expression:

{ pkgs ? import <nixpkgs> {} }:
let
  my-dep = pkgs.haskellPackages.mkDerivation {
    pname = "my-dep";
    version = "0.1.0.0";
    src = ./my-dep;
    isLibrary=true;
    isExecutable=false;
    license = with pkgs; stdenv.lib.licenses.unfree;
    doHaddock=false;
  };
  dependencies = with pkgs.haskellPackages; [
    aeson my-dep
  ];
  ghc = pkgs.haskellPackages.ghcWithPackages(hs:(dependencies));
in
pkgs.haskellPackages.mkDerivation {
  pname = "haskell-project";
  version = "0.1.0.0";
  src = ./src;
  isLibrary = false;
  isExecutable = true;
  buildTools = [ghc];
  buildDepends = dependencies;
  license = with pkgs; stdenv.lib.licenses.unfree;
}

(library expose 1 function which print text and main project just imports
aeson and my-dep and uses function from library)

When building it, I am getting error:

--------------------------------
Building haskell-project-0.1.0.0...
Preprocessing executable 'haskell-project' for haskell-project-0.1.0.0...

Main.hs:2:18:
    Could not find module ‘MyDep’
    Use -v to see a list of the files searched for.
builder for
‘/nix/store/43lbwp4qfigjwkf97nqp4h21hsrf5yr2-haskell-project-0.1.0.0.drv’
failed with exit code 1
error: build of
‘/nix/store/43lbwp4qfigjwkf97nqp4h21hsrf5yr2-haskell-project-0.1.0.0.drv’
failed
------------------------------------

There is no problem with aeson (it's complaining about aeson when I remove
dependency from nix expression), but there is a problem with my-dep
dependency.

Question is, how I should declare dependency for my-dep to make it working,
to make haskell-project to use that dependency correctly?

(if I run nix-shell with this expression I have the same error, but if I
"cd" to my-dep directory and run ghc ../src/Main.hs it's working, it looks
like ghs tries search for MyDep.hs only in current directory instead of
package directory).
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