Add als executable as dependency of test-suite

[juliapath]

I want to fix #33, so that this just works under nix, ideally without requiring any special treatment on the nix side. There are currently two problems stopping the package from building (without providing specific configuration):

• network-simple being pinned to 0.4.2
• The test suite not finding the als executable

This addresses the second one by making cabal add the als executable to PATH when running cabal test.

To be honest, I don't know how thiss interacts with other workflows, so I'm waiting to see if the GitHub Actions go through and for your comment. :)

[banacorn]

Thanks, this looks useful.

I don’t expect this to interfere with our current workflows in any major way. Our CI is still Stack-based, so this change is mainly relevant for cabal test / Nix-style builds rather than the existing CI path.

So yes, I think this is worth pursuing.

[sagehane]

I tried to build the server today and hit the exact same two issues. My "downstream" workaround for the test suite was to add this to the Nix expression:

                preCheck = ''
                  export PATH="$PWD/dist/build/als:$PATH"
                '';

Does seem to be code smell that one would need to add this to path for the test to work.

[juliapath]

Yes, but unfortunately this seems to be the way of doing things currently. There are a bunch of Haskell packages that have this fix defined in Nixpkgs. The most ridiculous is Cabal2Nix which has a special case for the generation of it's own nix expression hardcoded for this exact issue. Because nix interacts with Setup.hs instead of thorough cabal, build-tools and build-tool-depends don't work for making the executable available during testing.