I added verbatim: cabal-version: 3.12 to my package.yaml in order to get access to PackageInfo_XXX. However, this turned out to cause problems when specifying internal-libraries (i.e. cabal sublibraries) in hpack: After cabal version 3.4 you need to specify sublibraries explicitily.

This is fixed in my package.yaml by specifying dependencies to my internal libraries as mypackage:myinternal. I first thought of this as a bug, but cabal says the purpose is to let users have a sublibrary with the same name as some external dependency. So I'm not sure how hpack will consider names of internal libraries? As now, hpack should make it clear in the documentation that references to internal-libraries fields must be written in the form <mypackage>:<myinternal> .

References: https://cabal.readthedocs.io/en/stable/cabal-package-description-file.html#library .