Add a replacement protect-first-parent hook

  hooks:

  - id: gitlint

- repo: https://github.com/jumanjihouse/pre-commit-hooks

  rev: 2.1.5

  hooks:

  - id: protect-first-parent

- repo: local

  hooks:

  - id: copyright-notice

    entry: hooks/squash.py

    pass_filenames: false

    stages: [push]

  - id: protect-first-parent

    name: Check for "git pull" violations

    language: python

    entry: hooks/first_parent.py

    pass_filenames: false

    stages: [merge-commit, commit, push]

- repo: https://github.com/pre-commit/pygrep-hooks

  rev: v1.8.0

  entry: check-for-squash

  pass_filenames: false

  stages: [push]

- id: protect-first-parent

  name: Check for "git pull" violations

  language: python

  entry: check-first-parent

  always_run: true

  pass_filenames: false

  stages: [merge-commit, commit, push]

#!/usr/bin/env python3

#  Copyright 2021  Dominik Sekotill <dom.sekotill@kodo.org.uk>

#

#  Licensed under the Apache License, Version 2.0 (the "License");

#  you may not use this file except in compliance with the License.

#  You may obtain a copy of the License at

#

#      http://www.apache.org/licenses/LICENSE-2.0

#

#  Unless required by applicable law or agreed to in writing, software

#  distributed under the License is distributed on an "AS IS" BASIS,

#  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

#  See the License for the specific language governing permissions and

#  limitations under the License.

"""

Check that the first-parent commit graph includes the upstream branch

The first-parent graph is the linear graph of commits which always follows the first parent

of any merge commits.  It is often seen as the canonical commit graph, with any n-th parent

lines (where n is greater than 1) seen as merged topic branches.

This hook checks that the upstream head exists in the first-parent graph and blocks

a commit or push if it does not.  If there is no upstream branch, this hook always allows

the commit/push to go ahead.

For some background reading on the situation where an upstream head is not on the

first-parent graph (dubbed a "foxtrot merge") I suggest the following article:

  - https://bit-booster.blogspot.com/2016/02/no-foxtrots-allowed.html

"""

import sys

from subprocess import PIPE

from subprocess import CalledProcessError

from subprocess import run

from typing import Optional

from typing import Set

FAIL_MSG = """

[FAIL] The upstream branch {upstream} is not on the first-parent linear commit graph.

You probably ran "git pull" without --rebase.  If you see this message as output from

"git pull" then abort with "git merge --abort" and re-run "git pull --rebase"; otherwise try

running "git rebase".

"""

def get_fp_commits(ref: str) -> Set[str]:

	"""

	Return the set of commits that are in the first-parent linear graph from ref

	"""

	cmd = ['git', 'rev-list', '--first-parent', ref]

	proc = run(cmd, stdout=PIPE, text=True, check=True)

	if proc.stdout is None:

		raise RuntimeError

	return set(proc.stdout.split())

def resolve_ref(ref: str) -> Optional[str]:

	"""

	Return a named head for a given ref, or None if there is no head

	If 'ref' does not exist None is also returned.

	"""

	cmd = ['git', 'rev-parse', '--abbrev-ref', ref]

	try:

		proc = run(cmd, stdout=PIPE, text=True, check=True)

	except CalledProcessError as exc:

		if exc.returncode == 128:

			return None

		raise

	return proc.stdout.strip() or None

def main() -> None:

	"""

	CLI entrypoint

	"""

	if not resolve_ref('@{upstream}'):

		return

	head_commits = get_fp_commits('HEAD')

	upstream_commits = get_fp_commits('@{upstream}')

	if not upstream_commits.difference(head_commits):

		return

	sys.stderr.write(FAIL_MSG.format(upstream=resolve_ref('@{upstream}')))

	sys.exit(1)

if __name__ == '__main__':

	main()

[tool.flit.scripts]

check-copyright-notice = "hooks.copyright:main"

check-for-squash = "hooks.squash:main"

check-first-parent = "hooks.first_parent:main"

[tool.isort]

force_single_line = true