Obtain branch name in CI environment

Adds support to obtain the name of the git branch associated to the
current commit in CI environments. In this scenarios, the commit is
checked out in detached HEAD state, which does not allow to obtain the
name of the branch via Git. CI services such as Gitlab, Jenkins, Travis,
etc. define a variable name that contains the name of the branch, which
is what this code looks for in order to define the CI service-agnostic
GIT_BRANCH variable.

cli/popper/config.py

@@ -21,22 +21,16 @@ def __init__(self, engine_name=None, resman_name=None, config_file=None,
         self.skip_pull = skip_pull
         self.skip_clone = skip_clone
 
-        # attempt to create a git.Repo. If folder doesn't exist, we get None
+        # if no git repository exists in workspace_dir or its parents, the repo
+        # variable is None and all git_* variables are assigned to 'na'
         self.repo = scm.new_repo(self.workspace_dir)
+        self.git_commit = scm.get_sha(self.repo)
+        self.git_sha_short = scm.get_sha(self.repo, short=7)
+        self.git_branch = scm.get_branch(self.repo)
 
-        if self.repo:
-            sha = self.repo.head.object.hexsha
-            self.git_commit = self.repo.git.rev_parse(sha)
-            self.git_sha_short = self.repo.git.rev_parse(sha, short=7)
-            if self.repo.head.is_detached:
-                self.git_branch = self.git_sha_short
-            else:
-                self.git_branch = self.repo.active_branch.name
-        else:
-            self.git_commit = 'na'
-            self.git_sha_short = 'na'
-            self.git_branch = 'na'
-
+        # wid is used to associate a unique id to this workspace. This is then
+        # used by runners to name resources in a way that there is no name
+        # clash between concurrent workflows being executed
         wid = shake_256(self.workspace_dir.encode('utf-8')).hexdigest(4)
         self.wid = wid
 

cli/popper/scm.py

@@ -155,3 +155,43 @@ def parse(url):
     log.debug(f'  version: {version}')
 
     return service_url, service, user, repo, step_dir, version
+
+
+def get_sha(repo, short=None):
+    """Returns the commit id for the currently checked out version on the
+    given repository object. If short is given, it is interpreted as the number
+    of characters from the SHA that get returned. E.g. short=7 returns the
+    first 7 characters, otherwise it returns the entire SHA1 string.
+    """
+    if not repo:
+        return 'na'
+
+    if short:
+        return repo.git.rev_parse(repo.head.object.hexsha, short=short)
+
+    return repo.git.rev_parse(repo.head.object.hexsha)
+
+
+def get_branch(repo):
+    """Get name of branch. If the repo is in detached head state, it looks for
+    for environment variables commonly used in CI services: TRAVIS_BRANCH,
+    GIT_BRANCH (Jenkins), CIRCLE_BRANCH and CI_COMMIT_REF_NAME (Gitlab)
+    """
+    if not repo:
+        return 'na'
+
+    if not repo.head.is_detached:
+        return repo.active_branch.name
+
+    branch = os.environ.get('TRAVIS_BRANCH')
+    if branch:
+        return branch
+    branch = os.environ.get('GIT_BRANCH')
+    if branch:
+        return branch
+    branch = os.environ.get('CIRCLE_BRANCH')
+    if branch:
+        return branch
+    branch = os.environ.get('CI_COMMIT_REF_NAME')
+    if branch:
+        return branch

cli/test/test_common.py

@@ -23,9 +23,16 @@ def mk_repo(self):
         readme = os.path.join(tempdir, 'README.md')
         open(readme, 'w').close()
 
+        # create first commit
         repo.index.add([readme])
         repo.index.commit('first commit')
 
+        # create second commit
+        with open(readme, 'w') as f:
+            f.write('README content\n')
+        repo.index.add([readme])
+        repo.index.commit('second commit')
+
         # create a remote
         repo.create_remote('origin', url='https://github.com/my/repo')
 

cli/test/test_scm.py

@@ -25,6 +25,26 @@ def test_get_remote_url(self):
 
         self.assertEqual(scm.get_remote_url(None), '')
 
+    def test_get_branch_in_detached_head_state(self):
+        repo = self.mk_repo()
+        repo.git.checkout('HEAD~1')
+
+        os.environ['TRAVIS_BRANCH'] = 'travis'
+        self.assertEqual('travis', scm.get_branch(repo))
+        os.environ.pop('TRAVIS_BRANCH')
+
+        os.environ['GIT_BRANCH'] = 'jenkins'
+        self.assertEqual('jenkins', scm.get_branch(repo))
+        os.environ.pop('GIT_BRANCH')
+
+        os.environ['CIRCLE_BRANCH'] = 'circle'
+        self.assertEqual('circle', scm.get_branch(repo))
+        os.environ.pop('CIRCLE_BRANCH')
+
+        os.environ['CI_COMMIT_REF_NAME'] = 'gitlab'
+        self.assertEqual('gitlab', scm.get_branch(repo))
+        os.environ.pop('CI_COMMIT_REF_NAME')
+
     def test_clone(self):
         tempdir = tempfile.mkdtemp()
         tdir = os.path.join(tempdir, 'test_clone')