Git submodule track branch

I want to test out having a submodule in a repository and having it be tracking a branch such that when the submodule is updated, it fetches the latest commits of that branch as well as when a change is made in the submodule directory, it is possible to commit and push that change from that directory to the submodule repository from within the context of the main repository.

Here's what I did and tried. I am hoping to build a full checklist at the end of this experiment. No guarantees this actually worked until this text states so, for now I am only messing around.

• Create the main repository

  https://github.com/TomasHubelbauer/git-submodule-track-branch

• Create the submodule repository

  https://github.com/TomasHubelbauer/git-submodule-track-branch-sub

• Add the submodule repository to the main repository

  git submodule add --branch main https://github.com/TomasHubelbauer/git-submodule-track-branch-sub sub
  cd sub
  git status
  # On branch main
  # Your branch is up to date with 'origin/main'.
  cd ..

  git submodule set-branch can be used instead of --branch in a later stage.

  . is a special value for --branch which should make the submodule track a branch by the same name as the branch of the main repository, but I was not able to make this work in Git 2.39 on macOS:

  fatal: 'origin/.' is not a commit and a branch '.' cannot be created from it

  If anything goes wrong in this step, this is how adding the submodule can be fully undone to try again with a clean slate:

  git rm -f .gitmodules
  git rm -f sub
  rm -rf .git/modules/sub
  # .git/config
  git config --remove-section submodule.sub

  -f is used to delete the path regardless of whether it has unstaged changes. git config --file .gitmodules --remove-section submodule.sub can be used if wanting to remove a single of multiple submodules instead of nuking the file.

  In GitHub, the submodule "directory" will still link to the tree of the given commit, it will not respect --branch and take you to the repository tree at that branch. :/

• Make a change in the submodule repository and verify pulling it in the main repository after adding submodule

  git submodule update --remote
  git status
  # modified:   sub (new commits)
  cd sub
  git status
  # HEAD detached at ??????

  I was able to pull the changes but it looks like it broke the remote branch tracking of the submodule? Although multiple pulls in a row seem to work… I wonder if this is just how Git displays things but it is still tracking?

  I can't consider this to be done yet until it doesn't break push after the pull.

• Make a change in the submodule directory and verify pushing it to the submodule repository after adding submodule

  Since with the initial pull and then an attempt at a push I am running into issues I would like to try and see if pushing right after adding the module with tracking will work?

  I will reset the state of the repository by removing the module completely and will try the push first.

• Make a change in the submodule repository and verify pulling it in the main repository after pushing first

  This is dependent on the above step working and most likely will itself work but again wipe the state of the tracking.

• Make a change in the submodule directory and verify pushing it to the submodule repository after pulling first

  cd sub
  git status
  # HEAD detached at ??????
  echo "- Added a change to the submodule directory for push to the repository" >> README.md
  git add *
  git status
  # modified:   README.md
  git commit -m "Made a change from the submodule directory in the main repository" -m "Not in the submodule repository!"
  # 1 file changed, 1 insertion(+)
  git status
  # HEAD detached from ??????
  # nothing to commit, working tree clean
  git push
  # fatal: You are not currently on a branch.
  # To push the history leading to the current (detached HEAD) state now, use
  # git push origin HEAD:<name-of-remote-branch>
  
  # TODO:
  git status
  cd ..
  git submodule update --remote
  git status