C. One big repo, haskell-foo’s debian/ files in haskell-foo/debian/
[...]
But there are also disadvantages:
* Slightly unusual, so needs explanation.
* It is not possible to check out just one package. But maybe
that is a good thing, for such a tightly coupled package set.
* Some tools might need to be extended to support that well. For
example debcheckout would need to support a "subdirectory"
parameter in the url specified in Vcs-Git, similar to the
branch parameter.
* Tags needs to be qualified by the package name ("haskell
-foo/1.0-1" instead of "1.0-1"). This would need support in
debcommit, similar to how gbp supports --git-debian-tag which
can be set to "%(pkg)/%(version)".