automerge.py

# (c) 2020 Humu
# MIT License

from typing import Any

import github

AUTOMERGE_LABEL_NAME = 'automerge'


class Automerge:
    def __init__(self, githubClient: github.Github) -> None:
        self._github = githubClient

    def _hasAutomergeLabel(self, pr: github.PullRequest.PullRequest) -> bool:
        return any(label.name == AUTOMERGE_LABEL_NAME for label in pr.labels)

    def processWebhookEvent(self, eventType: str, eventJson: Any) -> None:
        # If a PR becomes green, merge it.
        # If new commits are pushed, a PR check fails, or the PR is closed, remove the label.

        if eventType == 'status':
            # https://developer.github.com/v3/activity/events/types/#statusevent
            repo = self._github.create_from_raw_data(
                github.Repository.Repository, eventJson['repository']
            )
            commit = self._github.create_from_raw_data(github.Commit.Commit, eventJson['commit'])
            # Shockingly, GitHub gives no way to get the PR associated with a 'status' event. You
            # need to search the list of PRs.
            matchingPr = next(
                (pr for pr in repo.get_pulls(sort='updated') if pr.head.sha == commit.sha), None
            )

            if matchingPr and self._hasAutomergeLabel(matchingPr):
                # Clean means green, unstable means yellow, which happens often with Reviewable,
                # for whatever reason. (If the PR is not accepted or one of our required checks is
                # failing, it'll be 'blocked'.)
                # https://developer.github.com/v4/enum/mergestatestatus/
                if matchingPr.mergeable_state in ('clean', 'unstable'):
                    matchingPr.merge(merge_method='squash')
                # If a check fails, we leave the label so that if it's a flaky test it can be rerun.
                # (If a test fails due to a code issue and new commits are pushed as a fix, the
                # label will be removed due to the 'synchronize' below.)
        elif eventType == 'pull_request':
            # https://developer.github.com/v3/activity/events/types/#pullrequestevent
            pr = self._github.create_from_raw_data(
                github.PullRequest.PullRequest, eventJson['pull_request']
            )
            if self._hasAutomergeLabel(pr):
                # 'synchonize' means new commits were pushed
                if eventJson['action'] == 'synchronize' or (
                    eventJson['action'] == 'closed' and not pr.merged
                ):
                    pr.remove_from_labels(AUTOMERGE_LABEL_NAME)
        elif eventType == 'pull_request_review':
            # https://developer.github.com/v3/activity/events/types/#pullrequestreviewevent
            pr = self._github.create_from_raw_data(
                github.PullRequest.PullRequest, eventJson['pull_request']
            )
            review = self._github.create_from_raw_data(
                github.PullRequestReview.PullRequestReview, eventJson['review']
            )
            # Some API docs have 'state' values capitalized, some lowercase. Why? Don't know.
            if eventJson['action'] == 'submitted' and review.state.lower() == 'changes_requested':
                if self._hasAutomergeLabel(pr):
                    pr.remove_from_labels(AUTOMERGE_LABEL_NAME)