charm-build --write-lock-file doesn't find the branch properly if multiple branches point to the git hash

[ajkavanagh]

Checklist

• Confirmed this is an issue with charm-tools, not charmstore-client
• Provide versions of tools used
• Described the feature or ways to replicate the issue

What version am I running?

I ran the following command: snap info charm and got the following ouput:

charm-tools 2.8.3 from PyPi

I am using: Ubuntu 20.04

Issue/Feature

The charm-build --write-lock-file command produces a build.lock file to lock the layers and python modules. For git repositories, it attempts to get the branch for the git hash so that the --use-lock-file-branches option can rebuild from the head of a branch, rather than be locked to a commit hash.

I expect/expected the following

If the branch selected is also pointing to another branch (say master) then I expect just the branch to be selected.

What I got

An example of the problem is:

    {
      "type": "python_module",
      "package": "charms.openstack",
      "url": "git+https://opendev.org/openstack/charms.openstack.git",
      "branch": "refs/heads/master\nrefs/heads/stable/21.04",
      "version": "bcd0c9b4b4a19d4a4125e0a6a3f808a843a74fa1",
      "vcs": "git"
    },

i.e. the branch points to master and to stable/21.04. It should probably only point to stable/21.04.

This then breaks rebuilds as the branch isn't a single branch!

Options

1. Filter out refs/heads/master (and refs/heads/main) from the list.
2. If more than one branch remains, then exit the build.

However, that doesn't seem terribly useful.

This is currently a "problem" with python modules that spec it as git+https://... with a @branch#egg=... option to specify the branch. We should probably feed this into the detection of the branch to select it specifically. Not entirely sure how to do this.

As an interim fix, do the first option just to keep things going.

[fnordahl]

Fixed by #607