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Haskell in Nixpkgs/NixOS

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For discussions and questions about Haskell with Nix, cabal2nix and haskellPackages in nixpkgs | Current Docs: https://nixos.org/manual/nixpkgs/unstable/#haskell | Current PR: https://github.com/nixos/nixpkgs/pulls?q=is%3Apr+is%3Aopen+head%3Ahaskell-updates | Maintainer Docs: https://github.com/NixOS/nixpkgs/blob/haskell-updates/pkgs/development/haskell-modules/HACKING.md | More Nix: #community:nixos.org | More Haskell: #haskell-space:matrix.org | Merger Schedule: https://cloud.maralorn.de/apps/calendar/p/H6migHmKX7xHoTFa/dayGridMonth/now | Join #haskell.nix:libera.chat for question about the alternative haskell.nix infrastructure138 Servers

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25 Oct 2025
@nrbray:matrix.orgNigel joined the room.09:30:09
26 Oct 2025
@ners:nixos.devners

I'm trying to build a project that has build-depends on both haskell-language-server and hls-plugin-api.
Getting the following error when trying to build it with Nix:

Error: [Cabal-7107]
Could not resolve dependencies:
[__0] trying: dosh-24.11 (user goal)
[__1] trying: lsp-client-0.4.0.0/installed-9paX9qIvVp6G32qMeolaRR (dependency of dosh)
[__2] next goal: hls-plugin-api (dependency of dosh)
[__2] rejecting: hls-plugin-api-2.11.0.0/installed-4lbla6iVQTHCJxg4ni6oA8 (conflict: lsp-client => lsp==2.7.0.1/installed-5hx47Y1LdOnAB7d5AgUCZ9, hls-plugin-api => lsp==2.7.0.1/installed-G2N8IrC9NSyIKEvHjZgyEW)
[__2] trying: hls-plugin-api-2.11.0.0/installed-IPU6Rknqm9R6YyD99rrbxT
[__3] next goal: haskell-language-server (dependency of dosh)
[__3] rejecting: haskell-language-server-2.11.0.0/installed-AGaYptnU925K1vcaCIwSpk (conflict: hls-plugin-api==2.11.0.0/installed-IPU6Rknqm9R6YyD99rrbxT, haskell-language-server => hls-plugin-api==2.11.0.0/installed-4lbla6iVQTHCJxg4ni6oA8)
[__3] fail (backjumping, conflict set: dosh, haskell-language-server, hls-plugin-api)

If I pin to nixos-25.05 it works, so it must be a recent breakage.

12:50:29
@maralorn:maralorn.demaralornWell, "breakage".12:55:39
@maralorn:maralorn.demaralornThe problem is that we are fixing hls with an overrideScope in config…-common.nix and that overlay one is not being applied to the exposed hls-plugin-api package.12:57:07
@maralorn:maralorn.demaralornMore generally when somehow beating hls into compiling I generally don’t consider downstream consumers who link against it. I wasn’t aware of their existence.12:58:12
@ners:nixos.devnersIt's a thing that should work (the usage is valid) but does not. It even used to work, but has stopped working. That's by definition a breakage. :)13:08:45
@ners:nixos.devners* It's a thing that should work (the usage is valid) but does not. It even used to work, but has stopped working due to recent changes. That's by definition a breakage. :)13:09:09

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