Stream: haskell-flake

Topic: Removing IFD

Srid (Dec 05 2023 at 14:47):

@Aravind Gopal opened https://github.com/srid/haskell-flake/pull/204 which removes the need for IFD in local packages.

But IFD is still used in dependency overrides; for eg., packages.foo.source will use IFD, via callCabal2nix or callHackage. The open question here is: how do we solve it?

cc @Shivaraj B H

Srid (Dec 05 2023 at 14:52):

We may have to borrow some ideas from https://horizon-haskell.net/

Srid (Dec 11 2023 at 15:31):

From @Aravind Gopal

maintaining package sets seems like the only possible way for this.

which is same as in horizon-haskell.

Hmm, I'll take a look at this as a next project. Ideally we want to define package sets in Nix expressions itself, and stick close to nixpkgs (unlike horizon).

Srid (Jan 09 2024 at 06:23):

Here's one way to solve this: https://github.com/srid/haskell-flake/pull/204#pullrequestreview-1809771568

Summary: copy over the hackage2nix/ callCabal2nix generated default.nix to a directory, and have the developer commit that to Git.

Srid (Jan 09 2024 at 06:24):

It looks like this (note: we overrode relude to test dependency override),

image.png

❯ cat .haskellSrc2nix/haskell-template.nix
{ mkDerivation, aeson, async, base, data-default, directory
, filepath, lib, mtl, optics-core, profunctors, relude, shower
, time, with-utf8
}:
mkDerivation {
  pname = "haskell-template";
  version = "0.1.0.0";
  src = /nix/store/51shzaxpi2abz3hfp4q05kcd1lls0lba-source;
  isLibrary = false;
  isExecutable = true;
  executableHaskellDepends = [
    aeson async base data-default directory filepath mtl optics-core
    profunctors relude shower time with-utf8
  ];
  homepage = "https://srid.ca/haskell-template";
  description = "A template for Haskell projects using Nix";
  license = lib.licenses.mit;
  mainProgram = "haskell-template";
}

But as you can see that hardcoded src = /nix/store/51shzaxpi2abz3hfp4q05kcd1lls0lba-source; is problematic. Looks like we have to do some hacky patching of this generated nix to have the src point back to the actual path.

Shivaraj B H (Jan 09 2024 at 06:33):

Looks like we have to do some hacky patching of this generated nix to have the src point back to the actual path.

AFAIR calling cabal2nix executable results in a relative path rather than a path linking to the /nix/store for local packages.

Srid (Jan 09 2024 at 07:04):

But note we are using callCabal2nix which passes nix store paths,

cf. src in https://github.com/NixOS/nixpkgs/blob/6a9382b8d1d9531be1a2fd611f3f91f30fb38678/pkgs/development/haskell-modules/make-package-set.nix#L140

Last updated: Sep 16 2024 at 19:45 UTC