Cannot build happy 2.x from hackage

[avdv]

Describe the bug
After updating the stackage snapshot to 2024-10-10, we get happy version 2.0.2 from hackage.

This version is no longer a simple executable but the package has been split into the command line tool and a library with multiple sublibraries.

First off, this means we have to declare dependencies between components of the library manually:

stack_snapshot(
     name = "stackage",
     components = { 
         "happy-lib": [                                                                                                                                                      
            "lib",                                                                                                                                                          
            "lib:grammar",                                                                                                                                                  
            "lib:backend-glr",                                                                                                                                              
            "lib:backend-lalr",                                                                                                                                             
            "lib:frontend",                                                                                                                                                 
            "lib:tabular",                                                                                                                                                  
        ],                                                                                                                                                                  
     },
     components_dependencies = {
        "happy-lib": repr({                                                                                                                                                 
            "lib:backend-glr": ["lib:grammar", "lib:tabular"],                                                                                                              
            "lib:backend-lalr": ["lib:grammar", "lib:tabular"],                                                                                                             
            "lib:frontend": ["lib:grammar"],                                                                                                                                
            "lib:happy-lib": ["lib:grammar", "lib:backend-glr", "lib:backend-lalr", "lib:frontend", "lib:tabular"],                                                         
            "lib:tabular": ["lib:grammar"],                                                                                                                                 
        }),                                                                                                                                                                 
     },
   ...
)

Next, the problem is that the happy-lib component is basically empty (ie. it does not produce a static nor shared library and no haddock) since it just re-exports modules from sub-libraries.

Furthermore, the backend sublibraries depend on the Paths_happy_lib module (see here) to locate its data-dir which fails at runtime since the location of the data-dir in the runfiles tree is completely different to what the Cabal generated (relocatable) Paths modules expects:

happy: /home/claudio/.cache/bazel/_bazel_claudio/f3d395587a4c32cd78e0bbc3318c2a29/execroot/rules_haskell_tests/bazel-out/k8-opt-exec-C7777A24/bin/external/stackage/happy-2.0.2/_install/happy-lib-2.0.2-backend-lalr_data/HappyTemplate.hs: openFile: does not exist (No such file or directory)

We would need to pass generate_paths_module = True to the haskell_cabal_libary stanzas generated by stack_snapshot. But that would also require patching the .cabal file to disable auto-generation of the Paths modules and add the runfiles library as a dependency. Probably the best option would be to vendor the sources in this case.

To Reproduce
Use stack_snapshot with happy >= 2 and try to run it as a tool.

Expected behavior
We should be able to build happy (and happy-lib).

Environment

• OS name + version: linux / nixOS
• Bazel version: 6.5.0
• Version of the rules: 1.0.0

Additional context
Add any other context about the problem here.

[iteratee]

Would it help to have support for an empty library that builds no .a file nor .so files, but still populates the package cache? Or would it be easier to just create a dummy module so that there is an actual library?

I made some progress on an empty haskell_cabal_library. Bazel will happily build it, but the package db ends up empty, which isn't what I was looking for.