rebase-helper fails to build with Sphinx 3.0.0.

sphinx-build-3 -b custom-man -d ../build/doctrees   . ../build/man
Running Sphinx v3.0.1
loading translations [en]... done
Exception occurred:
  File "/usr/lib/python3.8/site-packages/sphinx/application.py", line 1069, in add_source_parser
    self.registry.add_source_parser(*args, **kwargs)
TypeError: add_source_parser() takes 2 positional arguments but 3 were given

For the build logs, see:
https://copr-be.cloud.fedoraproject.org/results/cstratak/sphinx_3.0.0/fedora-rawhide-x86_64/01335428-rebase-helper/

For all our attempts to build rebase-helper with Sphinx 3.0.0, see:
https://copr.fedorainfracloud.org/coprs/cstratak/sphinx_3.0.0/package/rebase-helper/

Testing and mass rebuild of packages is happening in copr. You can follow these instructions to test locally in mock if your package builds with Sphinx 3:
https://copr.fedorainfracloud.org/coprs/cstratak/sphinx_3.0.0/

Let us know here if you have any questions.

Sphinx 3 will be included in Fedora 33. To make that update smoother, we're building the dependent packages in Copr.
We'd appreciate help from the people who know this package best, but if you don't want to work on this now, let us know so we can try to work around it on our side.