Nix CI is broken

[jgm]

See https://github.com/jgm/pandoc/actions/runs/12617858361/job/35160603870#step:6:2569

The problem seems to be that nix's cabal wrapper can't determine the version of happy, which is a build tool for toml-parser. happy is installed. happy --version returns

Happy Version 2.1.3 Copyright (c) 1993-1996 Andy Gill, Simon Marlow (c) 1997-2005 Simon Marlow

Happy is a Yacc for Haskell, and comes with ABSOLUTELY NO WARRANTY.
This program is free software; you can redistribute it and/or modify
it under the terms given in the file 'LICENSE' distributed with
the Happy sources.

which I'm guessing is not in the format cabal-wrapped expects?

So I think this is a bug in Haskell nix tooling, but I'm completely ignorant about how this works, so I'm hoping someone more knowledgeable can point me in the right direction or create an upstream bug report.

@tarleb
@srid
@peti

[peti]

Hi John, I don't think that error is related to Nix. The executable ".cabal-wrapped" is "cabal". It's just a renamed version of the cabal-install executable. The executable name "cabal" is used by a Nix-generated wrapper script that adds important tools to $PATH to make sure cabal finds them, but that's all there is to it. Nix doesn't know or care about happy. My guess is that the build uses an old version of cabal-install that can't deal with the relatively recent version of happy. So one could either upgrade the build to a newer cabal-install version or downgrade the version of happy to remedy this situation. Cheers, Peter

[jgm]

Thank you Peter. Both the cabal version and the happy version are the versions from the nixpkgs repository -- so, if what you say is right, isn't a problem with nix if these don't work together?

In any case, I'd be happy to be told how to change default.nix to specify either a newer cabal-install version or an older happy version. I'm sorry, I don't know nix well enough.

[jgm]

PS. I'd been assuming that the cabal-wrapped business was something pkgs.haskellPackages.developPackage used to parse a cabal file and extract the nix dependencies...and thus not part of cabal.

[srid]

On a general note, the CI workflow uses nix-shell which is impure (nix-shell uses shell.nix which imports nixpkgs using impure channels; see here) whereas nix develop is pure (nixpkgs is pinned to a commit if nixpkgs is referenced as flake input). So switching entirely to flakes would solve purity issues like this. I did hit some issues when I tried last time (#9952), and perhaps someone else would like pick that up ...