Passing Cabal flags

[sheepforce]

I'm currently trying to deal with the problems described in haskell/haskell-language-server#365 where TemplateHaskell code with C dependencies breaks the HLS for a module. The suggested workaround (and it is not a nice one) is to use CPP magic to eliminate the problem causing code for HLS and switch it out by a stub. I'm doing so via cpp-options in cabal, which are themselves triggered by a cabal flag.

Basically I want cabal -fdevelop for HLS and cabal -f-develop for everything else. Is it somehow possible using the hie-bios to pass such flags to HLS?

[fendor]

Hi, thank you for the bug report!

Currently, there is no released HLS version that allows this, iirc, since it would depend on the relatively new version 0.13.0 of hie-bios. However, once haskell/haskell-language-server#3462 is merged, the following should work.

I think you can specify flags in cabal.project files, right?
Then you can create a cabal.hls.project file, specify the packages and flags.
You can instruct HLS to use this cabal.project.hls file by creating a hie.yaml file with the contents:

cradle:
  cabal:
    cabalProject: "cabal.hls.project"

[sheepforce]

I think you can specify flags in cabal.project files, right?

Yes, this was also something I've tried and setting the flag there also works

Then you can create a cabal.hls.project file, specify the packages and flags. You can instruct HLS to use this cabal.project.hls file by creating a hie.yaml file with the contents:

This looks very good and exactly like a solution to my problem. Unfortunately HLS -> GHCIDE does not support the hie-bios 0.13.0 where this was introduced, yet 😬 I guess this solution also has to wait for the next HLS, then?

[fendor]

Yes, or build the PR from source and give it a spin. Compiling from source is easy with ghcup :)

Otherwise, I am afraid wait for the release that incorporates hie-bios 0.13.0, I can imagine there will be a release with that version this year, but I can't promise.

[sheepforce]

Thank you very much! I'm on a Nix setup as my project has some crazy Python, Fortran and C deps and I wasn't successful yet with building the HLS form the PR there. 😬

I will report back when the HLS with hie-bios 0.13.0 becomes available, but I'm very optimistic that it solves this problem :)

[sheepforce]

Alright, HLS 2.6 and the hie-bios 0.13.1 made it to nixkgs (at least in the haskell-updates branch). I'm using a hie.yaml file that contains

cradle:
  cabal:
    cabalProject: "nix-cabal.project"

and starting the HLS it also gets this option passed:

$ haskell-language-server-wrapper 
Found "/home/phillip/Dokumente/Git/Spicy/spicy-chemistry/hie.yaml" for "/home/phillip/Dokumente/Git/Spicy/spicy-chemistry/a"
Run entered for haskell-language-server-wrapper(haskell-language-server-wrapper) Version 2.6.0.0 x86_64 ghc-9.6.4
Current directory: /home/phillip/Dokumente/Git/Spicy/spicy-chemistry
Operating system: linux
Arguments: []
Cradle directory: /home/phillip/Dokumente/Git/Spicy/spicy-chemistry
Cradle type: Cabal

Tool versions found on the $PATH
cabal:          3.10.2.1
stack:          Not found
ghc:            9.6.4


Consulting the cradle to get project GHC version...
2024-01-26T10:06:42.011792Z | Debug | cabal exec --project-file /home/phillip/Dokumente/Git/Spicy/spicy-chemistry/nix-cabal.project -v0 -- ghc --print-libdir
Failed to find the GHC version of this Cabal project.
Error when calling cabal exec --project-file /home/phillip/Dokumente/Git/Spicy/spicy-chemistry/nix-cabal.project -v0 -- ghc --print-libdir

When using configuration(s) from /home/phillip/Dokumente/Git/Spicy/nix-cabal.project, the following errors occurred:
The package directory '.' does not contain any .cabal file.

But apparently the option doesn't work as expected. Indeed cabal exec --project-file /home/phillip/Dokumente/Git/Spicy/spicy-chemistry/nix-cabal.project -v0 -- ghc --print-libdir gives the same error also when run independently. However, giving only the relative path to the project file works flawlessly:

$ cabal exec --project-file=nix-cabal.project -v0 -- ghc --print-libdir
/nix/store/nsiq29cbm67byvh8rm4dn7gnf42ndcsi-ghc-9.6.4-with-packages/lib/ghc-9.6.4/lib

Am I doing something wrong here? 🙂

[fendor]

Hm, looks like project-file option is deprecated. I get the warning

Warning: Specifying an absolute path to the project file is deprecated. Use
--project-dir to set the project's directory.

on my cabal HEAD binary.

what's the output without the -v0 flag?

[fendor]

I can not reproduce:

$ cabal-3.10.2.1 exec --project-file /home/hugin/Documents/haskell/eventlog2html/cabal.project -- ghc --print-libdir
Resolving dependencies...
/home/hugin/.ghcup/ghc/9.4.8/lib/ghc-9.4.8/lib
$ cabal-3.10.1.0 exec --project-file /home/hugin/Documents/haskell/eventlog2html/cabal.project -- ghc --print-libdir
Resolving dependencies...
/home/hugin/.ghcup/ghc/9.4.8/lib/ghc-9.4.8/lib
$  cabal-3.6.2.0 exec --project-file /home/hugin/Documents/haskell/eventlog2html/cabal.project -- ghc --print-libdir 
Resolving dependencies...
/home/hugin/.ghcup/ghc/9.4.8/lib/ghc-9.4.8/lib

[fendor]

This cabal issue may be relevant: haskell/cabal#7695

PR that explains the warning above: haskell/cabal#8454

[sheepforce]

Hm, but it's not me who is generating this option. It directly comes from hie-bios/HLS, doesn't it? Even if I change my hie.yaml to

cradle:
  cabal:
    cabalProject: ./nix-cabal.project

and be explicit about being a relative path haskell-language-server-wrapper generates the path absolute in the cabal call. So I can use --project-file $RELATIVE_PATH or --project-dir $ABSOLUTE_PATH and that's perfectly fine. But how do I tell hie-bios/HLS to do so?

EDIT: the otuput without -v0 is

When using configuration(s) from /home/phillip/Dokumente/Git/Spicy/nix-cabal.project, the following errors occurred:
The package directory '.' does not contain any .cabal file.

[sheepforce]

Ah nevermind. The problem is something different. I have a monorepo with many subprojects. The nix-cabal.project resides in the top-level directory and is symlinked into each subproject. For some reasons it resolves the project directory to the top-level directory, not to that of the subproject. If I instead copy the nix-cabal.project file into the subproject it just works. A little bit surprising behaviour but I can deal with that 😄

[fendor]

Yeah, the behaviour of --project-file seems to be surprising... We will have to rethink our approach, as currently we force the absolute path.

[sheepforce]

Indeed 😄 But easy to work around if one's aware. However, the cabalProject option solved my problem exactly as you've advertised. If you'd like we can close the ticket :) Thank you very much! 🐑

[fendor]

Closing it for now, thanks for verifying it works (roughly) as advertised!