Regression in HEAD leading to build path leaking into object files (preprocessors)

[mpickering]

In Cabal HEAD, when hsc2hs is invoked an absolute path is passed which then leaks into the object files due to this path being used in a LINE pragma.

In older versions of Cabal this is a relative path which doesn't include the build directory.

I suspect this is due to work performed by @sheaf so I will coordinate investigations with him to investigate a fix.

[mpickering]

Seems that preprocessFile requires an argument of type Maybe (SymbolicPath CWD (Dir Pkg)) but then the filepath which arrives is "/home/matt/mercury-web-backend/zlib-0.7.1.0/", notably not a relative path from CWD to (Dir Pkg).

[mpickering]

It seems this absolute path originates a long way back in cabal-install, so I am a bit wary of changing it. I will talk with Sam.

[mpickering]

This is the change which seems to fix things for local source packages.

 readSourcePackageLocalDirectory verbosity dir cabalFile = do
   monitorFiles [monitorFileHashed cabalFile]
   root <- askRoot
-  let location = LocalUnpackedPackage (root </> dir)
+  let location = LocalUnpackedPackage dir

[Kleidukos]

@mpickering If I understand wwell, the dir in question has already been resolved to be an absolute path?

[mpickering]

@Kleidukos 3.12 doesn't have this regression but it's important to fix before 3.14 I believe.

[Kleidukos]

Quite right indeed.

[Kleidukos]

@mpickering Have you coordinated with @sheaf for a fix?

[sheaf]

Yes, Matthew fixed this in #10256 (now merged).