DO NOT MERGE: Experiment with cron

.github/workflows/pull_request.yml

@@ -0,0 +1,19 @@
+on:
+  schedule:
+    - cron: '* * * * *'
+name: Synchronize the Pull Request Preview
+jobs:
+  update-pr-preview:
+    runs-on: ubuntu-18.04
+    steps:
+    - uses: actions/checkout@v1
+      with:
+        ref: refs/heads/master
+        fetch-depth: 50
+    - name: update-pr-preview
+      uses: ./tools/docker/github
+      env:
+        GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+      with:
+        entrypoint: python
+        args: tools/ci/update_pr_preview.py https://api.github.com

tools/ci/update_pr_preview.py

@@ -0,0 +1,172 @@
+import json
+import logging
+import os
+import random
+import sys
+
+import requests
+
+active_label = 'pull-request-has-preview'
+
+logging.basicConfig(level=logging.INFO)
+logger = logging.getLogger(__name__)
+
+
+class Status(object):
+    SUCCESS = 0
+    FAIL = 1
+    NEUTRAL = 0
+
+
+def request(url, method_name, data=None, json_data=None, ignore_body=False):
+    github_token = os.environ.get('GITHUB_TOKEN')
+
+    kwargs = {
+        'headers': {
+            'Authorization': 'token {}'.format(github_token),
+            'Accept': 'application/vnd.github.machine-man-preview+json'
+        }
+    }
+    method = getattr(requests, method_name)
+
+    logger.info('Issuing request: {} {}'.format(method_name.upper(), url))
+    if json_data is not None or data is not None:
+        kwargs['json'] = json_data
+        kwargs['data'] = data
+
+    resp = method(url, **kwargs)
+
+    resp.raise_for_status()
+
+    if not ignore_body:
+        return resp.json()
+
+
+def resource_exists(url):
+    try:
+        request(url, 'get', ignore_body=True)
+    except requests.HTTPError as exception:
+        if exception.response.status_code == 404:
+            return False
+        raise
+
+    return True
+
+
+class GitHub(object):
+    def __init__(self, api_root, owner, repo):
+        self.api_root = api_root
+        self.owner = owner
+        self.repo = repo
+
+    def is_collaborator(self, login):
+        return resource_exists(
+            '{}/repos/{}/{}/collaborators/{}'.format(
+                self.api_root, self.owner, self.repo, login
+            )
+        )
+
+    def ref_exists(self, ref):
+        return resource_exists(
+            '{}/repos/{}/{}/git/refs/{}'.format(
+                self.api_root, self.owner, self.repo, ref
+            )
+        )
+
+    def create_ref(self, ref, sha):
+        data = {
+            'ref': 'refs/{}'.format(ref),
+            'sha': sha
+        }
+        url = '{}/repos/{}/{}/git/refs'.format(
+            self.api_root, self.owner, self.repo
+        )
+
+        logger.info('Creating ref "{}" as {}'.format(ref, sha))
+
+        request(url, 'post', json_data=data)
+
+    def update_ref(self, ref, sha):
+        data = {
+            'force': True,
+            'sha': sha
+        }
+        url = '{}/repos/{}/{}/git/refs/{}'.format(
+            self.api_root, self.owner, self.repo, ref
+        )
+
+        logger.info('Updating ref "{}" as {}'.format(ref, sha))
+
+        request(url, 'patch', json_data=data)
+
+    def delete_ref(self, ref):
+        url = '{}/repos/{}/{}/git/refs/{}'.format(
+            self.api_root, self.owner, self.repo, ref
+        )
+
+        logger.info('Deleting ref "{}"'.format(ref))
+
+        try:
+            request(url, 'delete', ignore_body=True)
+        except requests.HTTPError as exception:
+            if exception.response.status_code != 404:
+                raise
+
+            logger.info(
+                'Attempted to delete non-existent ref: {}'.format(ref)
+            )
+
+    def set_ref(self, ref, sha):
+        if self.ref_exists(ref):
+            self.update_ref(ref, sha)
+        else:
+            self.create_ref(ref, sha)
+
+    def add_label(self, pr_number, label_name):
+        data = {
+            'labels': [label_name]
+        }
+        url = '{}/repos/{}/{}/issues/{}/labels'.format(
+            self.api_root, self.owner, self.repo, pr_number
+        )
+
+        logger.info('Adding label')
+
+        request(url, 'post', json_data=data)
+
+    def remove_label(self, pr_number, label_name):
+        url = '{}/repos/{}/{}/issues/{}/labels/{}'.format(
+            self.api_root, self.owner, self.repo, pr_number, label_name
+        )
+
+        logger.info('Removing label')
+
+        try:
+            request(url, 'delete')
+        except requests.HTTPError as exception:
+            if exception.response.status_code != 404:
+                raise
+
+            logger.info(
+                'Attempted to remove non-existent label: {}'.format(label_name)
+            )
+
+
+def main(api_root):
+    with open(os.environ['GITHUB_EVENT_PATH']) as handle:
+        event = json.load(handle)
+        logger.info(json.dumps(event, indent=2))
+
+    owner, repo = os.environ['GITHUB_REPOSITORY'].split('/', 1)
+    github = GitHub(api_root, owner, repo)
+    sha = '8be01b6e0d191a641f45ad59e83718155775921d'
+    name = 'heads/random-%d' % (random.random() * 1000)
+    github.set_ref(name, sha)
+
+    return Status.SUCCESS
+
+
+if __name__ == '__main__':
+    code = main(sys.argv[1])
+    assert isinstance(code, int)
+    sys.exit(code)