Failure: twisted.internet.utils._UnexpectedErrorOutput: got stderr: "fatal: ambiguous argument 'master..origin/master': unknown revision or path not in the working tree.\nUse '--' to separate paths from revisions\n"
It turned out that the problem was that the git subprocesses weren’t inheriting my environment which has
SSH_AUTH_SOCK environment variables to make ssh to GitHub work.
The effect of the patch is that when calling external git commands, the environment is passed so that crucial environment variables like
SSH_AUTH_SOCK get propagated. Otherwise, Buildbot will not be able to make use of ssh keys with passphrases that are cached by