def _get_git_branch()

in builder/core/env.py [0:0]
42 lines of code
16 McCabe index (conditional complexity)

    def _get_git_branch():
        travis_pr_branch = os.environ.get("TRAVIS_PULL_REQUEST_BRANCH")
        if travis_pr_branch:
            print("Found branch:", travis_pr_branch)
            return travis_pr_branch

        # NOTE: head_ref only set for pull_request events
        # see: https://docs.github.com/en/actions/reference/environment-variables#default-environment-variables
        github_head_ref = os.environ.get("GITHUB_HEAD_REF")
        github_ref = os.environ.get("GITHUB_REF")
        if github_head_ref:
            # if we are triggered from a PR then we are in a detached head state (e.g. `refs/pull/:prNumber/merge`)
            # and we need to grab the branch being merged from
            # see: https://docs.github.com/en/actions/reference/events-that-trigger-workflows#pull_request
            branch = github_head_ref
            print("Found github ref for PR from: {}".format(branch))
            return branch
        elif github_ref:
            origin_str = "refs/heads/"
            if github_ref.startswith(origin_str):
                branch = github_ref[len(origin_str):]
                print("Found github ref: {}".format(branch))
                return branch

        try:
            branches = subprocess.check_output(
                ["git", "branch", "-a", "--contains", "HEAD"]).decode("utf-8")
            star_branch = None
            for branch in branches.split('\n'):
                if branch and branch.startswith('*'):
                    star_branch = branch.strip('*').strip()
                    break
            branches = [branch.strip('*').strip()
                        for branch in branches.split('\n') if branch]

            print("Found branches:", branches)

            # if git branch says we're on a branch, that's it
            if star_branch:
                print('Working in branch: {}'.format(star_branch))
                return star_branch

            # pick the first one (it should be the only one, if it's a fresh sync)
            for branch in branches:
                if branch == "(no branch)":
                    continue

                origin_str = "remotes/origin/"
                if branch.startswith(origin_str):
                    branch = branch[len(origin_str):]

                print('Working in branch: {}'.format(branch))
                return branch
        except:
            print("Current directory () is not a git repository".format(os.getcwd()))

        # git symbolic-ref --short HEAD
        return 'main'