Add script to cherry-pick PR commits for backports

diff --git a/build-scripts/cherry-pick-pr.py b/build-scripts/cherry-pick-pr.py
new file mode 100755 (executable)
index 0000000..c455d81
--- /dev/null
+++ b/build-scripts/cherry-pick-pr.py
@@ -0,0 +1,59 @@
+#!/usr/bin/env python3
+
+import requests
+import sys
+import subprocess
+import argparse
+
+
+def get_commits(pr):
+    try:
+        res = requests.get('https://api.github.com/repos/PowerDNS/pdns/pulls/'
+                           '{}/commits'.format(pr)).json()
+        return [c['sha'] for c in res]
+    except (ValueError, requests.exceptions.HTTPError) as e:
+        print(e)
+        sys.exit(1)
+
+
+def run_command(cmd):
+    try:
+        subprocess.check_call(cmd)
+    except subprocess.CalledProcessError as e:
+        print(e)
+        sys.exit(1)
+
+
+a = argparse.ArgumentParser()
+action = a.add_mutually_exclusive_group(required=True)
+action.add_argument(
+    '-b', '--backport-unto', metavar='REF', nargs=1, help='Backport, using '
+    'cherry-pick, all commits from PULL_REQUEST onto REF. This is done on a '
+    'branch called "backport-PULL_REQUEST". When the cherry-pick fails, solve '
+    'the conflict as usual and run "git cherry-pick --continue --allow-empty"')
+action.add_argument(
+    '-m', '--merge-into', metavar='REF', nargs=1, help='Take the backport-'
+    'PULL_REQUEST branch and merge it into REF')
+a.add_argument(
+    'pull_request', metavar='PULL_REQUEST', type=int,
+    help='The PR number to backport')
+
+args = a.parse_args()
+
+if args.backport_unto:
+    command = ['git', 'checkout', '-b',
+               'backport-{}'.format(args.pull_request), args.backport_unto[0]]
+    run_command(command)
+
+    commits = get_commits(args.pull_request)
+    command = ['git', 'cherry-pick', '-x', '--allow-empty'] + commits
+    run_command(command)
+
+if args.merge_into:
+    command = ['git', 'checkout', args.merge_into[0]]
+    run_command(command)
+
+    command = ['git', 'merge', '--no-ff',
+               'backport-{}'.format(args.pull_request), '-m',
+               'Backport #{}'.format(args.pull_request)]
+    run_command(command)