Exception on repo().active_branch.name

[grumpyp]

Setup

Running on GitPython==3.1.27

MacOS monterey, Python 3.10.5

Reproduce the bug

git checkout <commit> -> leads to a detached HEAD

from pathlib import Path
from git import Repo

def repo() -> 'Repo':
    from git import Repo  # type: ignore
    return Repo(Path(__file__).parent, search_parent_directories=True)

repository = repo()
repository.active_branch.name    

Error log

❯ python3 test.py
Traceback (most recent call last):
  File "/test.py", line 9, in <module>
    repository.active_branch.name
  File "/venv/lib/python3.10/site-packages/git/repo/base.py", line 797, in active_branch
    return self.head.reference
  File "/venv/lib/python3.10/site-packages/git/refs/symbolic.py", line 294, in _get_reference
    raise TypeError("%s is a detached symbolic reference as it points to %r" % (self, sha))
TypeError: HEAD is a detached symbolic reference as it points to '7sfaslkhfuhajkfnjaksdhfc4ede32c'

visual proof

[Byron]

This is intended behaviour, despite not being 'nice'.

The exception is not just any exception, but it states exactly why there is no active branch:

TypeError: HEAD is a detached symbolic reference as it points to '7sfaslkhfuhajkfnjaksdhfc4ede32c'

At this point, there is no way to fix this property, but in case you would like to add a new one, like try_active_branch or something that returns None instead, PRs are always welcome.

[grumpyp]

Hi @Byron, probably a fix in the documentation would help users as well.

I was looking for an error in my code for a while until I noticed that it's not my fault.

Thanks.

[Byron]

Definitely, if exceptions are used to communicate errors they should be documented, and a PR for that is welcome as well.

[grumpyp]

@Byron opened a PR here

For everyone else:

You can prevent the execution of the Exception by doing something like this:

if repo().head.is_detached:
   print("foo")