The process to create these files is as follows:

1. Run stack2cabal
2. Disable tests and benchmarks of local packages
   (those specified via source-repository-package...
   this won't be needed with cabal-3.4 anymore, because it won't treat
   them as local anymore)
3. Hackage packages in `packages` in `cardano-1.19.x.yaml` or `extra-deps`
   in `stack.yaml`, which are specified as git repositories might
   have different versions than the stack resolver. `stack2cabal`
   cannot pick these up, so these must be adjusted manually (or deleted) in
   `cabal.project.freeze` (at the time of writing: http-client and persistent).

Rationale:

1. good to support all available tools as options for interested users
2. cabal allows easier managing of package bounds (and testing against
   latest package versions and different GHCs, because it is not
   constrained to stackage)
3. doesn't require nix, which is an additional step to set up and
   maintain and requires significant amount of disk space

This is mainly due to a cabal bug and should be removed in
the future: haskell/cabal#5444

There are various distros, where installing development files
of libsystemd won't be an option:

- Alpine (doesn't have systemd at all)
- Gentoo (not installable when eudev is installed)
- Exherbo (not installable when eudev is installed)

Users are expected to run the script and then execute cabal like so:

  cabal build --project-file=cabal.nosystemd.project all

Also see haskellari/time-compat#10

The Haskell.nix shellFor function provides Haskell package
dependencies and all their dependencies.

This new nix/cabal-shell.nix file only provides a compiler, build
tools and system libraries, and lets Cabal build the Haskell package
dependencies.

Using nix-shell and "cabal build --project-file=cabal-nix.project",
all Haskell dependencies will be downloaded from the IOHK cache,
rather than built locally.