Add a hook checking for commits that need squashing

    require_serial: true

    types: [python]

    stages: [commit]

  - id: check-for-squash

    name: Check for commits that need squashing

    language: system

    entry: hooks/squash.py

    pass_filenames: false

    stages: [push]

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

  rev: v1.5.1

  require_serial: true

  types: [python]

  stages: [commit]

- id: check-for-squash

  name: Check for commits that need squashing

  language: python

  entry: check-for-squash

  pass_filenames: false

  stages: [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.

"""

Block commit starting with "squash!" or "fixup!" from being pushed

These commits must be squashed before a push to a remote

"""

import os

import sys

from collections import defaultdict

from pathlib import Path

from subprocess import PIPE

from subprocess import Popen

Z40 = '0' * 40

GIT_EXEC_PATH = 'GIT_EXEC_PATH'

PRE_COMMIT_TO_REF = 'PRE_COMMIT_TO_REF'

PRE_COMMIT_FROM_REF = 'PRE_COMMIT_FROM_REF'

class CommitDict(defaultdict):

	"""

	A dict for holding Commit objects mapped from their subject lines

	"""

	def __missing__(self, subject):

		self[subject] = commit = Commit(subject)

		return commit

class Commit:

	"""

	A class for holding information about regular commits

	"""

	__slots__ = 'subject', 'sha', 'updates'

	def __init__(self, subject: str, sha: str = Z40):

		if len(sha) != 40 or not sha.isalnum():

			raise ValueError("'sha' must be a SHA-1 hash")

		self.subject = subject.strip()

		self.sha = sha

		self.updates = []

def git_log_cmd():

	"""

	Return the first arguments for running a git-log command

	"""

	if GIT_EXEC_PATH in os.environ:

		git_log = Path.cwd() / os.environ[GIT_EXEC_PATH] / 'git-log'

		if git_log.exists() and git_log.stat().st_mode & os.X_OK:

			return [git_log]

	return ['git', 'log']

def catalogue_commits():

	"""

	Yield all regular commits as Commit objects, containing any update (squash) commits

	"""

	cmd = git_log_cmd()

	cmd.extend([

		'--reverse',

		'--format=format:%H %s',

		f"{os.environ[PRE_COMMIT_FROM_REF]}...{os.environ[PRE_COMMIT_TO_REF]}",

	])

	commits = CommitDict()

	with Popen(cmd, stdout=PIPE, text=True) as proc:

		for line in proc.stdout.readlines():

			sha, _, subject = line.partition(' ')

			keyword, has_marker, target = subject.partition('! ')

			if has_marker and keyword in ('squash', 'fixup'):

				# Squash commit, add it to its target list

				commits[target].updates.append(sha)

				continue

			if subject in commits:

				# Regular commit, but another exists with the same message, so yield the

				# previous one first

				yield commits.pop(subject)

			commits[subject] = Commit(subject, sha)

	yield from commits.values()

def main():

	"""

	CLI entrypoint

	"""

	retcode = 0

	output = sys.stderr.write

	for commit in catalogue_commits():

		if not commit.updates:

			continue

		if not retcode:

			retcode = 1

			output("The following commits need to be squashed before pushing:\n\n")

		output("  target:\n")

		output(

			f"    {commit.subject[:60]}\n" if commit.sha == Z40 else

			f"    {commit.subject[:60]} ({commit.sha[:8]})\n",

		)

		output("  commits:\n")

		output(f"    {', '.join(commit.updates)}\n")

		if commit.sha == Z40:

			output("  note:\n")

			output("    The target for the above commits is not part of this update set.\n")

			output("    You should squash them into a new commit.\n")

		output("\n")

	sys.exit(retcode)

if __name__ == '__main__':

	main()

[tool.flit.scripts]

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

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

[tool.isort]

force_single_line = true