"""
🔴 Branch not mergeable

mergeable jobset failed.
maintained jobset failed.

"""

I guess this is the no-go reason?

In reply to @a12l:matrix.org
If I'd GHCUp it looks like it would work flawlessly, but from what I gather it doesn't work on NixOS?

Unless it does something special on NixOS (I know modern Stack does), the GHC binaries that ghcup downloads are almost certainly dynamically linked and for that reason alone will not work.

Only fully statically linked executables work as-is on NixOS because they don't hardcode assumptions about how files are organised on the host.

GHC does more though: it needs to execute a C compiler and AFAIK that compiler cannot live in the same executable. Most NixOS systems don't have any C compiler installed in an easy-to-find location.

In reply to @a12l:matrix.org
I'm currently doing Exercism's Haskell exercises. They use stack (lts-20.18) for setting up dependencies etc. What's the best way to integrate it with Nix? If it's possible I simple want some tool that automatically download and install the correct version of GHC, HLS, and the dependencies for the project

Have you tried using Stack on NixOS? It might just work. I'm not sure.

You should get Stack from Nixpkgs, not from ghcup.

My current setup is having added

environment.systemPackages =
  [
    pkgs.ghc
    pkgs.cabal-install
    pkgs.haskell-language-server
    pkgs.haskellPackages.hlint
    pkgs.stack
  ];

in my NixOS config. When I run the tests by executing stack test in the exercise dir everything seems to work, it runs the test with GHC 9.2 (I've 9.6 globally installed) with dependencies.

But from what I understand, I've HLS compiled against my globally installed GHC version (9.6) instead of the one used in the project (9.2). Not 100 percent sure about that. Does HLS need to be specified in some stack file for it to installed?

When I replace pkgs.haskell-language-server with

(pkgs.haskell-language-server.override {
    supportedGhcVersions = [ "96" "92" ];
})

I get this error when trying nixos-rebuild switch --flake .#:

error: builder for '/nix/store/yx5ff3wha9qva80d7gpca686xjqx4kkn-haskell-language-server-2.9.0.0.drv' failed with exit code 1;
       last 25 log lines:
       > [11 of 13] Compiling Development.IDE.Plugin.Plugins.FillTypeWildcard ( plugins/hls-refactor-plugin/src/Development/IDE/Plugin/Plugins/FillTypeWildcard.hs, dist/build/hls-refactor-plugin/Development/IDE/Plugin/Plugins/FillTypeWildcard.p_o )
       > [12 of 13] Compiling Development.IDE.Plugin.Plugins.ImportUtils ( plugins/hls-refactor-plugin/src/Development/IDE/Plugin/Plugins/ImportUtils.hs, dist/build/hls-refactor-plugin/Development/IDE/Plugin/Plugins/ImportUtils.p_o )
       > [13 of 13] Compiling Development.IDE.Plugin.CodeAction ( plugins/hls-refactor-plugin/src/Development/IDE/Plugin/CodeAction.hs, dist/build/hls-refactor-plugin/Development/IDE/Plugin/CodeAction.p_o )
       > Preprocessing library 'hls-splice-plugin' for haskell-language-server-2.9.0.0..
       > Building library 'hls-splice-plugin' for haskell-language-server-2.9.0.0..
       >
       > <no location info>: warning: [-Wunused-packages]
       >     The following packages were specified via -package or -package-id flags,
       >     but were not needed for compilation:
       >       - ghc-exactprint-1.5.0-9oRXq6HKU5w30oFpO632kK
       > [1 of 2] Compiling Ide.Plugin.Splice.Types ( plugins/hls-splice-plugin/src/Ide/Plugin/Splice/Types.hs, dist/build/hls-splice-plugin/Ide/Plugin/Splice/Types.o, dist/build/hls-splice-plugin/Ide/Plugin/Splice/Types.dyn_o )
       > [2 of 2] Compiling Ide.Plugin.Splice ( plugins/hls-splice-plugin/src/Ide/Plugin/Splice.hs, dist/build/hls-splice-plugin/Ide/Plugin/Splice.o, dist/build/hls-splice-plugin/Ide/Plugin/Splice.dyn_o )
       >
       > <no location info>: warning: [-Wunused-packages]
       >     The following packages were specified via -package or -package-id flags,
       >     but were not needed for compilation:
       >       - ghc-exactprint-1.5.0-9oRXq6HKU5w30oFpO632kK
       > [1 of 2] Compiling Ide.Plugin.Splice.Types ( plugins/hls-splice-plugin/src/Ide/Plugin/Splice/Types.hs, dist/build/hls-splice-plugin/Ide/Plugin/Splice/Types.p_o )
       > [2 of 2] Compiling Ide.Plugin.Splice ( plugins/hls-splice-plugin/src/Ide/Plugin/Splice.hs, dist/build/hls-splice-plugin/Ide/Plugin/Splice.p_o )
       > Preprocessing library 'hls-retrie-plugin' for haskell-language-server-2.9.0.0..
       > Building library 'hls-retrie-plugin' for haskell-language-server-2.9.0.0..
       > [1 of 1] Compiling Ide.Plugin.Retrie ( plugins/hls-retrie-plugin/src/Ide/Plugin/Retrie.hs, dist/build/hls-retrie-plugin/Ide/Plugin/Retrie.o, dist/build/hls-retrie-plugin/Ide/Plugin/Retrie.dyn_o )
       > [1 of 1] Compiling Ide.Plugin.Retrie ( plugins/hls-retrie-plugin/src/Ide/Plugin/Retrie.hs, dist/build/hls-retrie-plugin/Ide/Plugin/Retrie.p_o )
       > /nix/store/1mv8pj4nxwnd9bbxshljc9p4cnl3rakj-binutils-wrapper-2.43.1/bin/ranlib: dist/build/hls-retrie-plugin/libHShaskell-language-server-2.9.0.0-BRo8Gg6usq8JRcUr14mEwc-hls-retrie-plugin-ghc9.2.8.a: error reading Internal.o: No space left on device
       > `ranlib' failed in phase `Ranlib'. (Exit code: 1)
       For full logs, run 'nix log /nix/store/yx5ff3wha9qva80d7gpca686xjqx4kkn-haskell-language-server-2.9.0.0.drv'.
error: 1 dependencies of derivation '/nix/store/zvansnmsfmx29cpgq008l7vxs66fswh0-haskell-language-server-2.9.0.0.drv' failed to build
error: 1 dependencies of derivation '/nix/store/vi2lbfb8m6dqbn6ffwkzxmk84fx730mr-system-path.drv' failed to build
error: 1 dependencies of derivation '/nix/store/fdr0jpvadmrh41ahzlcd47036h76v9v6-nixos-system-p-desktop2-24.11.20250323.f0946fa.drv' failed to build

No errors when I use

(pkgs.haskell-language-server.overrideAttrs (old: {
  supportedGhcVersions = [ "96" "92" ];
}))

Unsure about the difference between override and overrideAttrs