Reopen Pull Requests with the Github API

Using the Github API to reopen auto-closed Pull Requests

December 29, 2018

Problem Statement

At work, we typically deploy once a day from a hotfix branch that looks something like hotfix/2.9.1.3. Once deployed to master, the branch is deleted, the hotfix version number is incremented, and a new branch hotfix/2.9.1.4 is created. Some of this creation / deletion of branches is automated by hubflow for us.

This process has an annoying side effect - all current open pull requests to hotfix/2.9.1.3 will be automatically closed by Github, as the base branch (the branch you would like to merge code into) no longer exists. After a deployment, we would have to go to Github and manually reopen all of the closed pull requests.

The Solution

Of course, there must be a better way. We need two things from Github, and done in the following order:

Change the base branch of a closed pull request
Reopen a closed pull request

To help us interact with the Github API, I used pygithub. I set up a class to encapsulate the logic:

class GithubAPI(object):
    """
    Interact with the Github API
    """
    def __init__(self):
        self.access_token = settings.ACCESS_TOKEN
        self.username = settings.ACCESS_USERNAME

        # instantiate instance to communicate with Github
        self.github = Github(self.access_token)

        # instantiate instance to our repo
        self.repo = self.github.get_repo("our/repo")

Before we can do anything, we need to get the branches that are relevant to our problem. We need to get all unmerged Pull Requests (PR’s) to a particular branch. We can use get_pulls from pygithub to help us out. Here’s how to that:

def get_unmerged_closed_pull_requests(self, base_branch):
    """
    Get a list of unmerged, closed pull requests to a particular base_branch
    Args:
        (str) - base_branch - the base branch of the form hotfix/2.9.3.1
    Returns:
        (List[PullRequest]) - list of PullRequest objects
    """

    # these will be both merged and unmerged
    query = self.repo.get_pulls(state="closed", base=base_branch)

    # unmerged prs should have a None merged_at attribute
    return [pr for pr in query if not pr.merged_at]

Now that we can get PR’s we are interested in, we need change each PR’s base branch and reopen it. pygithub exposes an edit function on the PullRequest class to modify attributes of a pull request, so let’s use it:

def update_base_branches_and_open_prs(self, base_branch, new_base_branch):
    """
    Get all the PR's to the base_branch, change their branch bases to
    new_base_branch, and open them
    Args:
        (str) - base_branch - the base branch of the form hotfix/2.9.3.1
        (str) - new_base_branch - the new base branch to set prs to of form hotfix/2.9.3.2
    """

    relevant_prs = self.get_unmerged_closed_pull_requests(base_branch)

    # update to new_base_branch and reopen
    for pr in relevant_prs:
        try:
            log.info(u"Updating PR: {0}".format(pr.title))
            pr.edit(base=new_base_branch)
            pr.edit(state="open")

        except Exception:
            log.exception(u"Unable to update Pr {title}".format(title=pr.title))

The function update_base_branches_and_open_prs accepts the previous and new base branches and attempts to reopen each of the PR’s from get_unmerged_closed_pull_requests.

We can now run this from a python intepretor:

In [1]: from app.somewhere import GithubAPI
In [2]: g = GithubAPI()
In [3]: g.update_base_branches_and_open_prs("hotfix/2.9.3.10", "hotfix/2.9.3.11")

Nice! We can attach this to our deployment process and have a function automatically run these commands. However, the process does not currently only reopen autoclosed pull requests. Can you find the edge case that we missed?

One more case: non-autoclosed Pull Requests

What if you closed a pull request because you were either not ready to merge it, or it is no longer relevant? The script would still reopen your PR, and that is not what we want. We can solve this by tapping into the events of a Pull Request and only reopen PR’s that were autoclosed.

I couldn’t find something that indicated whether a Pull Request was autoclosed, but it turned out that we have one specific Github user that closed Pull Requests (the admin of the repo) which we only used for administrative tasks. We can choose PR’s that were only closed by this Github user:

def update_base_branches_and_open_prs(self, base_branch, new_base_branch):
    """
    Get all the PR's to the base_branch, change their branch bases to
    new_base_branch, and open them
    Args:
        (str) - base_branch - the base branch of the form hotfix/2.9.3.1
        (str) - new_base_branch - the new base branch to set prs to of form hotfix/2.9.3.2
    """

    relevant_prs = self.get_unmerged_closed_pull_requests(base_branch)

    # update to new_base_branch and reopen
    for pr in relevant_prs:
        try:

            # we only want to update PR's that were closed by githubadmin as they are auto-closed
            events = self.get_events_for_pull_request(pr)
            last_event = events[-1]
            if last_event["event"] == "closed" and last_event["actor"]["login"] == "githubadmin":
                log.info(u"Updating PR: {0}".format(pr.title))
                pr.edit(base=new_base_branch)
                pr.edit(state="open")
            else:
                log.info(u"PR {0} was not autoclosed, skipping".format(pr.title))
        except Exception:
            log.exception(u"Unable to update Pr {title}".format(title=pr.title))

Last thing to do is to actually get the events for a pull request. pygithub didn’t seem to provide a direct way to get these, so we have to make a request to the Github API for this information:

def get_events_for_pull_request(self, pull_request):
    """
    Get the events associated with a particular PullRequest object
    Args:
        pull_request (github.PullRequest.PullRequest) - representation of a Pull Request
    Returns:
        HTTP response with events for a Pull Request
    """
    issue_url = pull_request._rawData['issue_url']

    request_url = "{0}/events".format(issue_url)
    auth_obj = HTTPBasicAuth(
        self.username,
        self.access_token
    )
    try:
        response = json.loads(requests.get(request_url, auth=auth_obj).content)
    except Exception:
        log.info(u"Unable to get events for PR {title}".format(title=pull_request.title))
        response = None

    return response

And we’re done!

I’m Jonathan Mares, I'm a software engineer based in Walnut Creek, CA. Follow me on Twitter!