update_prs.py

#!/usr/bin/env python3

import functools
import git
import github
import tempfile
import textwrap

changes_requested_label = 'changes requested'
merge_label = 'ready to merge'
rebase_label = 'needs rebase'
review_label = 'needs review'

repo_url = ''
github_repo = ''
token = ''

def merge(target_branch, default_branch='develop'):
    with tempfile.TemporaryDirectory() as temp_dir:
        repo = git.Repo.clone_from(repo_url, temp_dir)
        origin = repo.remotes[0]

        try:
            repo.git.rebase('{0}/{1}'.format(origin.name, target_branch))
            origin.push('refs/heads/{0}:refs/heads/{0}'.format(default_branch))
            origin.push(':refs/heads/{0}'.format(target_branch))

            return True
        except git.GitCommandError:
            return False

def main():
    gh = github.Github(token)
    repo = gh.get_repo(github_repo)
    HEAD = repo.get_branch(repo.default_branch).commit.sha
    pulls = repo.get_pulls()

    for pull in pulls:
        commits = [commit for commit in pull.get_commits()]

        # Check if the parent(s) of the first commit of the PR is HEAD
        is_rebased = any(parent.sha == HEAD for parent in commits[0].parents)

        issue = repo.get_issue(pull.number)
        new_labels = [label.name for label in issue.labels]

        if changes_requested_label not in new_labels:
            for pr_commit in commits:
                message_lines = pr_commit.commit.message.split()
                if 50 < len(message_lines[0]):
                    pull.create_issue_comment(textwrap.dedent('''
                        Commit messages do not conform to best practices.
                        Please ensure your subject line (first line of the
                        message) is 50 characters or less. Each line of the
                        body should be 72 characters or less.
                    '''))
                    new_labels.append(changes_requested_label)
                    break

        if not is_rebased:
            new_labels.append(rebase_label)
        else:
            if rebase_label in new_labels:
                new_labels.remove(rebase_label)

        if len(new_labels) == 0 or new_labels == [rebase_label]:
            new_labels.append(review_label)

        new_labels = list(set(new_labels))
        issue.edit(labels=new_labels)

        statuses = functools.reduce(
            lambda x, y: x + y,
            [[s for s in c.get_statuses()] for c in commits]
        )

        failure = any(status.state == 'failure' for status in statuses)
        if not failure and new_labels == [merge_label]:
            print('Merging pull request #{0}'.format(pull.number))
            if merge(pull.head.ref, repo.default_branch):
                # Last commit of the merged PR becomes the new HEAD
                HEAD = commits[-1].sha
            else:
                pull.create_issue_comment(
                    ':warning: **Warning!** Failed to auto-merge.'
                )

if __name__ == '__main__':
    main()