Incorrect flags when loading multiple executable components on GHC 9.4

[Vic-M]

Hello, I'm not sure if this is a configuration issue with my hie.yaml, but I'm unable to get HLS to work with two Main.hs files at the same time. There's no issues with compiling both of them with cabal though.

Your environment

Which OS do you use?
Windows WSL2 running CentOS Stream 9

Which version of GHC do you use and how did you install it?
GHC 9.4.4 from ghcup

How is your project built (alternative: link to the project)?
https://gitlab.com/vmatassa/hls-two-main-example

Which LSP client (editor/plugin) do you use?
vscode

Which version of HLS do you use and how did you install it?
HLS 1.9.1.0 from ghcup

Steps to reproduce

1. Open projectA/app/Main.hs
2. Open projectB/app/Main.hs right after

Actual behaviour

HLS is unable to recognize libraries that are exclusively in projectB cabal's file.

Could not load module ‘Data.Aeson’
It is a member of the hidden package ‘aeson-2.1.2.1’.
Perhaps you need to add ‘aeson’ to the build-depends in your .cabal file.
It is a member of the hidden package ‘aeson-2.1.1.0’.
Perhaps you need to add ‘aeson’ to the build-depends in your .cabal file.
It is a member of the hidden package ‘aeson-2.1.1.0’.
Perhaps you need to add ‘aeson’ to the build-depends in your .cabal file.

Expected behaviour

HLS should be able to find installed libraries from all cabal files in the project.

[fendor]

Hi, thank you for your bug report!

I can reproduce on windows.
Maybe we use relative filepaths somewhere...

[georgefst]

I've just hit this immediately after upgrading from GHC 9.2.7 to 9.4.5.

(Well, that bump was actually in a Haskell.Nix project, which simultaneously upgraded HLS to the commit cda1325 for various reasons, having I think previously been using the 1.10.0.0 release. But I also see this error when using 1.10.0.0 on GHC 9.4.4, without Nix, so it seems likely that GHC 9.4, or its handling within HLS, is the culprit. But I can investigate further if it would be helpful.)

[L0neGamer]

My company upgraded to GHC 9.4.5 last thursday and we're getting similar issues with our HLS instances. We have multiple packages in the same project, and the ones marked as missing include both our own packages and ones like shakespeare-2.1.0, directory-1.3.7.1, and others.

Do the maintainers need any investigation on symptom-observers' behalf?

I compiled hls using ghcup compile hls -g 1.10.0.0 --ghc 9.4.5 --cabal-update, using 9.4.5 installed with ghcup.

[georgefst]

This stems from 6c99563, and commenting out the Set up a multi component session with the other units on GHC 9.4 CPP branch appears to fix the behaviour. I don't know whether it's worth opening a PR doing so for now, as it might have other undesirable effects. And maybe there's a mistake that's obvious to @wz1000, who wrote the code. I don't personally know the new home units API well enough to easily debug much further.

PS. thanks @fendor for pointing me in the right direction.

[georgefst]

(changing the title because I've been consistently seeing this with https://github.com/georgefst/evdev, in which the executables are defined in the same cabal file, and because it's now clear this is 9.4-specific)