-Werror=unused-packages cannot be satisfied for ghc-prim

Summary

My library package has a module which imports Ghc.Prim. If I use -Werror=unused-packages, ghc both requires ghc-prim to be listed as a dependency and requires it not to be listed as a dependency.

Steps to reproduce

Note: cabal is used here for convenience, but is not required to reproduce. The ghc commands to reproduce are also given here.

• have a cabal project for a library pacakge in the current directory
• have a source file with import Ghc.Prim, which is listed in exposed-modules in the cabal file
• cabal file's library.ghc-options includes -Werror=unused-packages
• when the cabal file's library.build-depends includes ghc-prim:

  • ghc -Werror=unused-packages src/A.hs -pacakge-id ghc-prim-0.8.0, or cabal build gives this error:

    <no location info>: error: [-Wunused-packages, -Werror=unused-packages]
    The following packages were specified via -package or -package-id flags,
    but were not needed for compilation:
      - ghc-prim-0.8.0

• when the cabal file's library.build-depends does not include ghc-prim:

  • ghc -Werror=unused-packages src/A.hs, or cabal build gives this error:

    src/A.hs:3:1: error:
    Could not find module ‘Ghc.Prim’
    Perhaps you meant GHC.Prim (needs flag -package-id ghc-prim-0.8.0)
    Use -v (or `:set -v` in ghci) to see a list of the files searched for.
      |
    3 | import Ghc.Prim
      | ^^^^^^^^^^^^^^^

Expected behavior

Since ghc-prim is required for compilation, -Werror=unused-packages should not error saying that it is not required.

Environment

• GHC version used: 9.2.5

Optional:

• Operating System: NixOS 22.11pre-git (Raccoon)
• System Architecture: x86_64