unused package warning always report main library

Even if the unused library is a sublibrary in Cabal package, I see e.g.

<no location info>: warning: [GHC-42258] [-Wunused-packages]
    The following packages were specified via -package or -package-id flags,
    but were not needed for compilation:
      - bytestring-0.12.1.0 (exposed by flag -package-id bytestring-0.12.1.0-2ee7)
      - lsm-tree-0.1.0.0 (exposed by flag -package-id lsm-tree-0.1.0.0-inplace-bloomfilter)

Note the lsm-tree-0.1.0.0-inplace-bloomfilter, which is lsm-tree:bloomfilter sublibrary. The warning is imprecise

(#24667 is very similar issue of GHC equating packages to libraries, which isn't true anymore)