It's a boot package, so it is shipped with ghc itself:

$ nix-shell -p ghc --command 'ghc-pkg list' | grep unix
    unix-2.8.4.0

Thanks, that helps a lot. So I guess Nix GHC 9.10 is providing unix-2.8.5.1. Nix GHC 9.12 provides unix-2.8.6.0. This explains why my package is not getting the version in haskellPackages, i.e.:

nix search nixpkgs/haskell-updates#haskellPackages '^unix'
* legacyPackages.x86_64-linux.haskellPackages.unix_2_8_6_0 (2.8.6.0)

this version is not the one used

Thanks, that helps a lot. So I guess Nix GHC 9.10 is providing unix-2.8.5.1. Nix GHC 9.12 provides unix-2.8.6.0. This explains why my package is not getting the version in haskellPackages, i.e.:

nix search nixpkgs/haskell-updates#haskellPackages '^unix'
* legacyPackages.x86_64-linux.haskellPackages.unix_2_8_6_0 (2.8.6.0)

this unix_2_8_6_0 is not the one used

on this topic, I actually have a question: would it generally be accepted to upstream haskell executables in that way? i.e. by using a package definition like so:

{haskellPackages, ...}: haskellPackages.callPackage {...}

In reply to @mangoiv.:matrix.org

on this topic, I actually have a question: would it generally be accepted to upstream haskell executables in that way? i.e. by using a package definition like so:

{haskellPackages, ...}: haskellPackages.callPackage {...}

After cabal2nix on a cabal repo which generated a default.nix, I've changed default.nix to add on my NixOS repo:

{ lib
, stdenv
, fetchFromGitHub
, ansi-terminal
, base
, containers
, directory
, filepath
, hs-highlight
, mtl
, parsec
}:

stdenv.mkDerivation rec {
  pname = "kind-lang";
  version = "unstable-2024-12-09";

  src = fetchFromGitHub {
    owner = "higherorderco";
    repo = "kind";
    rev = "5cfff210b3aeed01ebd73b2364cf9e5d2df658af";
    hash = "sha256-gHJ+eruwsybjRc5f1VWsof2jWQjuO/9nhOMKAvuMl7w=";
  };

  isLibrary = true;
  libraryHaskellDepends = [
    ansi-terminal
    base
    containers
    directory
    filepath
    hs-highlight
    mtl
    parsec
  ];

  isExecutable = true;
  executableHaskellDepends = [
    ansi-terminal
    base
    directory
    filepath
    hs-highlight
    mtl
  ];

  meta = with lib; {
    description = "A modern proof language";
    homepage = "https://github.com/higherorderco/kind";
    changelog = "https://github.com/higherorderco/kind/blob/${src.rev}/CHANGELOG.md";
    license = licenses.mit;
    maintainers = with maintainers; [ ];
  };
}

but

nix-build -E 'with import <nixpkgs> {}; haskellPackages.callPackage ./default.nix {}'
this derivation will be built:
  /nix/store/h8lp8csvwv90b38yj3nb36258i9vhjp7-kind-lang-unstable-2024-12-09.drv
building '/nix/store/h8lp8csvwv90b38yj3nb36258i9vhjp7-kind-lang-unstable-2024-12-09.drv'...
Running phase: unpackPhase
unpacking source archive /nix/store/g46qdc00anivc5fl16rb4xiwy73z512b-source
source root is source
Running phase: patchPhase
Running phase: updateAutotoolsGnuConfigScriptsPhase
Running phase: configurePhase
no configure script, doing nothing
Running phase: buildPhase
no Makefile or custom buildPhase, doing nothing
Running phase: installPhase
no Makefile or custom installPhase, doing nothing
Running phase: fixupPhase
error: builder for '/nix/store/h8lp8csvwv90b38yj3nb36258i9vhjp7-kind-lang-unstable-2024-12-09.drv' failed to produce output path for output 'out' at '/nix/store/h8lp8csvwv90b38yj3nb36258i9vhjp7-kind-lang-unstable-2024-12-09.drv.chroot/root/nix/store/bwh8lqpgh54jmi3f3x0nbm4v06x380vj-kind-lang-unstable-2024-12-09'

is cabal2nix really supposed to be used like this outside a cabal repo project? or this needs some fixing still?

After cabal2nix on a cabal repo which generated a default.nix, I've changed default.nix to add to my NixOS repo/config:

{ lib
, stdenv
, fetchFromGitHub
, ansi-terminal
, base
, containers
, directory
, filepath
, hs-highlight
, mtl
, parsec
}:

stdenv.mkDerivation rec {
  pname = "kind-lang";
  version = "unstable-2024-12-09";

  src = fetchFromGitHub {
    owner = "higherorderco";
    repo = "kind";
    rev = "5cfff210b3aeed01ebd73b2364cf9e5d2df658af";
    hash = "sha256-gHJ+eruwsybjRc5f1VWsof2jWQjuO/9nhOMKAvuMl7w=";
  };

  isLibrary = true;
  libraryHaskellDepends = [
    ansi-terminal
    base
    containers
    directory
    filepath
    hs-highlight
    mtl
    parsec
  ];

  isExecutable = true;
  executableHaskellDepends = [
    ansi-terminal
    base
    directory
    filepath
    hs-highlight
    mtl
  ];

  meta = with lib; {
    description = "A modern proof language";
    homepage = "https://github.com/higherorderco/kind";
    changelog = "https://github.com/higherorderco/kind/blob/${src.rev}/CHANGELOG.md";
    license = licenses.mit;
    maintainers = with maintainers; [ ];
  };
}

but

nix-build -E 'with import <nixpkgs> {}; haskellPackages.callPackage ./default.nix {}'
this derivation will be built:
  /nix/store/h8lp8csvwv90b38yj3nb36258i9vhjp7-kind-lang-unstable-2024-12-09.drv
building '/nix/store/h8lp8csvwv90b38yj3nb36258i9vhjp7-kind-lang-unstable-2024-12-09.drv'...
Running phase: unpackPhase
unpacking source archive /nix/store/g46qdc00anivc5fl16rb4xiwy73z512b-source
source root is source
Running phase: patchPhase
Running phase: updateAutotoolsGnuConfigScriptsPhase
Running phase: configurePhase
no configure script, doing nothing
Running phase: buildPhase
no Makefile or custom buildPhase, doing nothing
Running phase: installPhase
no Makefile or custom installPhase, doing nothing
Running phase: fixupPhase
error: builder for '/nix/store/h8lp8csvwv90b38yj3nb36258i9vhjp7-kind-lang-unstable-2024-12-09.drv' failed to produce output path for output 'out' at '/nix/store/h8lp8csvwv90b38yj3nb36258i9vhjp7-kind-lang-unstable-2024-12-09.drv.chroot/root/nix/store/bwh8lqpgh54jmi3f3x0nbm4v06x380vj-kind-lang-unstable-2024-12-09'

is cabal2nix really supposed to be used like this outside a cabal repo project? or this needs some fixing still?

In reply to @maralorn:maralorn.de
João Moreira: How did you encounter the breakage?

I made this derivation

{ lib
, mkDerivation
, fetchFromGitHub
, haskellPackages
}:

mkDerivation rec {
  pname = "kind-lang";
  version = "unstable-2024-12-09";

  src = fetchFromGitHub {
    owner = "higherorderco";
    repo = "kind";
    rev = "5cfff210b3aeed01ebd73b2364cf9e5d2df658af";
    hash = "sha256-gHJ+eruwsybjRc5f1VWsof2jWQjuO/9nhOMKAvuMl7w=";
  };

  postPatch = ''
    substituteInPlace kind-lang.cabal \
      --replace "==" "^>="
  '';

  isLibrary = false;
  isExecutable = true;

  libraryHaskellDepends = with haskellPackages; [
    ansi-terminal_1_1_1
    base_4_20_0_1
    containers_0_7
    directory_1_3_9_0
    filepath_1_5_3_0
    hs-highlight
    mtl_2_3_1
    parsec_3_1_17_0
  ];

  executableHaskellDepends = with haskellPackages; [
    ansi-terminal_1_1_1
    base_4_20_0_1
    directory_1_3_9_0
    filepath_1_5_3_0
    hs-highlight
    mtl_2_3_1
  ];

  # Test suite does nothing.
  doCheck = false;

  description = "A modern proof language";
  mainProgram = "kind";
  homepage = "https://github.com/higherorderco/kind";
  changelog = "https://github.com/higherorderco/kind/blob/${src.rev}/CHANGELOG.md";
  license = lib.licenses.mit;
  platforms = lib.platforms.linux;
  maintainers = with lib.maintainers; [ ];
}

then

nix-build -E 'with import <nixpkgs> {}; haskell.lib.compose.justStaticExecutables (haskellPackages.callPackage ./default.nix {})'
error:
       … while calling the 'derivationStrict' builtin
         at <nix/derivation-internal.nix>:34:12:
           33|
           34|   strict = derivationStrict drvAttrs;
             |            ^
           35|

       … while evaluating derivation 'kind-lang-unstable-2024-12-09'
         whose name attribute is located at /nix/store/c9wv7i0af6mysmy65x6nvyfw5izzxv4g-source/pkgs/stdenv/generic/make-derivation.nix:336:7

       … while evaluating attribute 'buildInputs' of derivation 'kind-lang-unstable-2024-12-09'
         at /nix/store/c9wv7i0af6mysmy65x6nvyfw5izzxv4g-source/pkgs/stdenv/generic/make-derivation.nix:383:7:
          382|       depsHostHost                = elemAt (elemAt dependencies 1) 0;
          383|       buildInputs                 = elemAt (elemAt dependencies 1) 1;
             |       ^
          384|       depsTargetTarget            = elemAt (elemAt dependencies 2) 0;

       (stack trace truncated; use '--show-trace' to show the full, detailed trace)

       error: Package ‘ghc-internal-9.1001.0’ in /nix/store/c9wv7i0af6mysmy65x6nvyfw5izzxv4g-source/pkgs/development/haskell-modules/hackage-packages.nix:121205 is marked as broken, refusing to evaluate.

Then I looked into https://github.com/NixOS/nixpkgs/blob/master/pkgs/development/haskell-modules/hackage-packages.nix#L121214

AND

• https://hydra.nixos.org/job/nixpkgs/haskell-updates/haskellPackages.ghc-internal.x86_64-linux#tabs-status
• https://cache.nixos.org/log/bxhkzb647jdfnr228kw4hrkrwz9bcm9k-ghc-internal-9.1001.0.drv

Error: Setup: Encountered missing or private dependencies:
ghc-prim >=0.11 && <0.12

But maybe that specific error not valid anymore

nix search nixpkgs#haskellPackages ghc-prim
* legacyPackages.x86_64-linux.haskellPackages.ghc-prim_0_11_0 (0.11.0)