Exception when running compile-time code when using autogenerated cabal `Paths_pkgname` module in template haskell

[NeuroCorgi]

Which OS do you use?
MacOS
Which version of GHC do you use and how did you install it?
GHC 9.10.1 with ghcup
How is your project built (alternative: link to the project)?
cabal build
Which LSP client (editor/plugin) do you use?
emacs+eglot
Which version of HLS do you use and how did you install it?
haskell-language-server 2.9.0.1 with ghcup

Steps to reproduce

When using autogenerated Paths_<pkgname> module from Cabal to read project files from a template haskell function, HLS reports an error diagnostic at the splice sites that use this function.

Reproducing project

reproducing project

project.cabal

cabal-version:      3.0
name:               project
version:            0.1.0.0
license:            MIT
license-file:       LICENSE
author:             NeuroCorgi
build-type:         Simple

executable project
    main-is:          Main.hs
    other-modules:    TH
                      Paths_project
    autogen-modules:  Paths_project
    build-depends:    base, template-haskell
    hs-source-dirs:   src
    default-language: Haskell2010

src/Main.hs

{-# LANGUAGE TemplateHaskell #-}

import TH

main :: IO ()
main = putStrLn $(embedFileFromProject "src/TH.hs")

src/TH.hs

module TH where

import System.IO
import Language.Haskell.TH

import qualified Paths_project as Paths

embedFileFromProject :: FilePath -> ExpQ
embedFileFromProject filePath = stringE =<< (runIO $ contents =<< Paths.getDataFileName filePath)
  where contents path = withFile path ReadMode hGetContents'

Expected behaviour

No diagnostic reported.

Actual behaviour

Diagnostic reported at the template haskell splice in src/Main.hs:

• Exception when trying to run compile-time code:
    /Users/neurocorgi/.cabal/share/aarch64-osx-ghc-9.10.1-64dd/project-0.1.0.0/src/TH.hs: withFile: does not exist (No such file or directory)
  Code: (embedFileFromProject "src/TH.hs")
• In the untyped splice: $(embedFileFromProject "src/TH.hs")

[fendor]

Hi, thank you for your bug report!

I think your example isn't quite correct, for example, cabal install fails with the error message:

> cabal install
Wrote tarball sdist to
/home/hugin/Documents/haskell/issues-hls/hls-reproduce/dist-newstyle/sdist/project-0.1.0.0.tar.gz
Resolving dependencies...
Build profile: -w ghc-9.6.7 -O1
In order, the following will be built (use -v for more details):
 - project-0.1.0.0 (exe:project) (requires build)
Starting     project-0.1.0.0 (exe:project)
Building     project-0.1.0.0 (exe:project)

Failed to build exe:project from project-0.1.0.0.
Build log (
/home/hugin/.cache/cabal/logs/ghc-9.6.7/project-0.1.0.0-e-project-ad861676a0877a40dbc4514112988a4044f938cd9a305469a0a30cacf99c6cb3.log
):
Configuring executable 'project' for project-0.1.0.0...
Preprocessing executable 'project' for project-0.1.0.0...
Building executable 'project' for project-0.1.0.0...
[1 of 3] Compiling Paths_project    ( dist/build/project/autogen/Paths_project.hs, dist/build/project/project-tmp/Paths_project.o, dist/build/project/project-tmp/Paths_project.dyn_o )
[2 of 3] Compiling TH               ( src/TH.hs, dist/build/project/project-tmp/TH.o, dist/build/project/project-tmp/TH.dyn_o )
[3 of 3] Compiling Main             ( src/Main.hs, dist/build/project/project-tmp/Main.o )

src/Main.hs:6:17: error: [GHC-87897]
    • Exception when trying to run compile-time code:
        /home/hugin/.local/state/cabal/store/ghc-9.6.7/project-0.1.0.0-e-project-ad861676a0877a40dbc4514112988a4044f938cd9a305469a0a30cacf99c6cb3/share/src/TH.hs: withFile: does not exist (No such file or directory)
      Code: (embedFileFromProject "src/TH.hs")
    • In the untyped splice: $(embedFileFromProject "src/TH.hs")
  |
6 | main = putStrLn $(embedFileFromProject "src/TH.hs")
  |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

You can have a look at https://hackage.haskell.org/package/file-embed-0.0.16.0/docs/src/Data.FileEmbed.html#embedFileRelative, which makes sure to change to the root directory before running the TH code.

[michaelpj]

This is a known issue, you have to use the makeRelativeToProject functions from file-embed if you want it to work reliably, as the working directory for TH code is not specified and can vary.