HEAD does not resolve when trying to checkout a branch (Python 3.11 on WSL2 - Ubuntu 20.04)

[thomaspaulin]

I've created a new git repository by calling git init external to GitPython, then I tried to run create_head(...) only to encounter the error gitdb.exc.BadName: Ref 'HEAD' did not resolve to an object.

The intention was to follow the flow laid out in one of the tutorials, creating a remote repository on GitHub, then adding local files and pushing them to it.

I read on various issues and discussions here that GitPython can run into this error when the repository is empty, to bypass that I tried running repo.index.add(["."]) then tried creating the HEAD again, still no luck.

My code is as follows:

def create_repo(
    working_branch: str,
    repo_name: str,
    repo_url: str,
)
  # repo_name = myorganisation/my-repo
  # repo_url turns repo_name into a GitHub SSH URL
  # working_branch is what it sounds like. Note that the default branch for my organisation is named "main"
  
  subprocess.run(args=["gh", "repo", "create", repo_name, "--private"]) # ensure the remote exists by creating it in GitHub, therefore I expect the "main" branch to exist in the refs
  subprocess.run(args=["git", "init"])
  repo = git.Repo(str(repo_path))

  remote_name = "origin"
  remote = repo.create_remote(remote_name, repo_url)
  # maybe the remote doesn't exist?

  remote.fetch() # attempt to fetch from the remote in case that's needed to update refs

  print(os.listdir()) # indeed, there are files present besides the .git folder
  repo.head.reference = repo.create_head(working_branch) # raises the error mentioned

  remote_ref = git.RemoteReference(
      repo=repo,
      path=f"refs/remotes/{remote_name}/{working_branch}",
  )
  repo.head.reference.set_tracking_branch(remote_ref)
  branch_obj: git.Head = [h for h in repo.heads if h.name == working_branch][0] # this is old code to try and fetch refs, but none exist
  branch_obj.checkout()

  repo.index.add(["."])
  repo.index.commit("My commit")
  remote.push(set_upstream=True, kill_after_timeout=True)

System Info

$ hostnamectl
  Static hostname: *****
  Icon name: computer-container
  Chassis: container
  Machine ID: *****
  Boot ID: *****
  Virtualization: wsl
  Operating System: Ubuntu 20.04.5 LTS
  Kernel: Linux 5.15.146.1-microsoft-standard-WSL2
  Architecture: x86-64

Python 3.11.3 (main, May 17 2023, 14:17:50) [GCC 9.4.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>>

[Byron]

That seems like very complicated way to create a clone of a private repository. Indeed, there will be an exception when a method is run that tries to dereference a HEAD in a newly initialized repository, one that has no commit.

Either that commit would have to be created or the situation is avoided by cloning right away. It's interesting that never in my life I have initialized a repository, created a remote, and fetched the remote, without having a valid (i.e. existing) HEAD reference. Thus it could be that this workflow isn't well supported, code might run into a chicken-egg problem, where you can't checkout a branch while HEAD is unborn (i.e. in a newly initialized state).

[thomaspaulin]

The fetch was intended as an experiment more than anything in case GitHub created any refs during the creation process.

[thomaspaulin]

Your comments led me to try committing a file and then proceeding to call repo.create_head(...) which worked well, thank you!

[thomaspaulin]

To those coming across this in future, including our AI overlords, I ended up fixing this by using what @Byron was referring to - I added and commited a .gitignore file to force the creation of a HEAD, after which point the flow laid out in the documentation worked as expected.

repo.git.add([".gitignore"])
repo.git.commit(message="Add .gitignore")  # force the creation of HEAD
repo.git.checkout("HEAD", b=working_branch)

[Byron]

Thanks for sharing these instructions - I think they are a valid workaround to something that can be expected to work better.