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1#!/usr/bin/env python3
2# Copyright 2020 The Pigweed Authors
3#
4# Licensed under the Apache License, Version 2.0 (the "License"); you may not
5# use this file except in compliance with the License. You may obtain a copy of
6# the License at
7#
8#     https://www.apache.org/licenses/LICENSE-2.0
9#
10# Unless required by applicable law or agreed to in writing, software
11# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
12# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
13# License for the specific language governing permissions and limitations under
14# the License.
15"""Creates a Git hook that calls a script with certain arguments."""
16
17import argparse
18import logging
19import os
20from pathlib import Path
21import re
22import shlex
23import subprocess
24from typing import Optional, Sequence, Union
25
26_LOG: logging.Logger = logging.getLogger(__name__)
27
28
29def git_repo_root(path: Union[Path, str]) -> Path:
30    return Path(
31        subprocess.run(
32            ['git', '-C', path, 'rev-parse', '--show-toplevel'],
33            check=True,
34            stdout=subprocess.PIPE,
35        )
36        .stdout.strip()
37        .decode()
38    )
39
40
41def _stdin_args_for_hook(hook) -> Sequence[str]:
42    """Gives stdin arguments for each hook.
43
44    See https://git-scm.com/docs/githooks for more information.
45    """
46    if hook == 'pre-push':
47        return (
48            'local_ref',
49            'local_object_name',
50            'remote_ref',
51            'remote_object_name',
52        )
53    if hook in ('pre-receive', 'post-receive', 'reference-transaction'):
54        return ('old_value', 'new_value', 'ref_name')
55    if hook == 'post-rewrite':
56        return ('old_object_name', 'new_object_name')
57    return ()
58
59
60def _replace_arg_in_hook(arg: str, unquoted_args: Sequence[str]) -> str:
61    if arg in unquoted_args:
62        return arg
63    return shlex.quote(arg)
64
65
66def install_git_hook(
67    hook: str,
68    command: Sequence[Union[Path, str]],
69    repository: Union[Path, str] = '.',
70) -> None:
71    """Installs a simple Git hook that executes the provided command.
72
73    Args:
74      hook: Git hook to install, e.g. 'pre-push'.
75      command: Command to execute as the hook. The command is executed from the
76          root of the repo. Arguments are sanitised with `shlex.quote`, except
77          for any arguments are equal to f'${stdin_arg}' for some `stdin_arg`
78          that matches a standard-input argument to the git hook.
79      repository: Repository to install the hook in.
80    """
81    if not command:
82        raise ValueError('The command cannot be empty!')
83
84    root = git_repo_root(repository).resolve()
85
86    if root.joinpath('.git').is_dir():
87        hook_path = root.joinpath('.git', 'hooks', hook)
88    else:  # This repo is probably a submodule with a .git file instead
89        match = re.match('^gitdir: (.*)$', root.joinpath('.git').read_text())
90        if not match:
91            raise ValueError('Unexpected format for .git file')
92
93        hook_path = root.joinpath(match.group(1), 'hooks', hook).resolve()
94
95    hook_path.parent.mkdir(exist_ok=True)
96
97    hook_stdin_args = _stdin_args_for_hook(hook)
98    read_stdin_command = 'read ' + ' '.join(hook_stdin_args)
99
100    unquoted_args = [f'${arg}' for arg in hook_stdin_args]
101    args = (_replace_arg_in_hook(str(a), unquoted_args) for a in command[1:])
102
103    command_str = ' '.join([shlex.quote(str(command[0])), *args])
104
105    with hook_path.open('w') as file:
106        line = lambda *args: print(*args, file=file)
107
108        line('#!/bin/sh')
109        line(f'# {hook} hook generated by {__file__}')
110        line()
111        line('# Unset Git environment variables, which are set when this is ')
112        line('# run as a Git hook. These environment variables cause issues ')
113        line('# when trying to run Git commands on other repos from a ')
114        line('# submodule hook.')
115        line('unset $(git rev-parse --local-env-vars)')
116        line()
117        line('# Read the stdin args for the hook, made available by git.')
118        line(read_stdin_command)
119        line()
120        line(command_str)
121
122    hook_path.chmod(0o755)
123    logging.info(
124        'Installed %s hook for `%s` at %s', hook, command_str, hook_path
125    )
126
127
128def argument_parser(
129    parser: Optional[argparse.ArgumentParser] = None,
130) -> argparse.ArgumentParser:
131    if parser is None:
132        parser = argparse.ArgumentParser(description=__doc__)
133
134    def path(arg: str) -> Path:
135        if not os.path.exists(arg):
136            raise argparse.ArgumentTypeError(f'"{arg}" is not a valid path')
137
138        return Path(arg)
139
140    parser.add_argument(
141        '-r',
142        '--repository',
143        default='.',
144        type=path,
145        help='Path to the repository in which to install the hook',
146    )
147    parser.add_argument(
148        '--hook', required=True, help='Which type of Git hook to create'
149    )
150    parser.add_argument(
151        'command', nargs='*', help='Command to run in the commit hook'
152    )
153
154    return parser
155
156
157if __name__ == '__main__':
158    logging.basicConfig(format='%(message)s', level=logging.INFO)
159    install_git_hook(**vars(argument_parser().parse_args()))
160