Add git_config module (#1945)

* Add git_config module

This module can be used for reading and writing git configuration at all
three scopes (local, global and system). It supports --diff and --check
out of the box.

This module is based off of the following gist:
https://gist.github.com/mgedmin/b38c74e2d25cb4f47908
I tidied it up and added support for the following:
- Reading values on top of writing them
- Reading and writing values at any scope
The original author is credited in the documentation for the module.

* Respond to review feedback

- Improve documentation by adding choices for parameters, requirements
  for module, and add missing description for scope parameter.
- Fail gracefully when git is not installed (followed example of puppet
  module).
- Remove trailing whitespace.

* Change repo parameter to type 'path'

This ensures that all paths are automatically expanded appropriately.

* Set locale to C before running commands to ensure consistent error messages

This is important to ensure error message parsing occurs correctly.

* Adjust comment

system/git_config.py

@@ -0,0 +1,219 @@
+#!/usr/bin/python
+# -*- coding: utf-8 -*-
+
+# (c) 2015, Marius Gedminas <marius@pov.lt>
+# (c) 2016, Matthew Gamble <git@matthewgamble.net>
+#
+# This file is part of Ansible
+#
+# Ansible is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# Ansible is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with Ansible.  If not, see <http://www.gnu.org/licenses/>.
+
+DOCUMENTATION = '''
+---
+module: git_config
+author:
+  - "Matthew Gamble"
+  - "Marius Gedminas"
+version_added: 2.1
+requirements: ['git']
+short_description: Read and write git configuration
+description:
+  - The M(git_config) module changes git configuration by invoking 'git config'.
+    This is needed if you don't want to use M(template) for the entire git
+    config file (e.g. because you need to change just C(user.email) in
+    /etc/.git/config).  Solutions involving M(command) are cumbersone or
+    don't work correctly in check mode.
+options:
+  list_all:
+    description:
+      - List all settings (optionally limited to a given I(scope))
+    required: false
+    choices: [ "yes", "no" ]
+    default: no
+  name:
+    description:
+      - The name of the setting. If no value is supplied, the value will
+        be read from the config if it has been set.
+    required: false
+    default: null
+  repo:
+    description:
+      - Path to a git repository for reading and writing values from a
+        specific repo.
+    required: false
+    default: null
+  scope:
+    description:
+      - Specify which scope to read/set values from. This is required
+        when setting config values. If this is set to local, you must
+        also specify the repo parameter. It defaults to system only when
+        not using I(list_all)=yes.
+    required: false
+    choices: [ "local", "global", "system" ]
+    default: null
+  value:
+    description:
+      - When specifying the name of a single setting, supply a value to
+        set that setting to the given value.
+    required: false
+    default: null
+'''
+
+EXAMPLES = '''
+# Set some settings in ~/.gitconfig
+- git_config: name=alias.ci scope=global value=commit
+- git_config: name=alias.st scope=global value=status
+
+# Or system-wide:
+- git_config: name=alias.remotev scope=system value="remote -v"
+- git_config: name=core.editor scope=global value=vim
+# scope=system is the default
+- git_config: name=alias.diffc value="diff --cached"
+- git_config: name=color.ui value=auto
+
+# Make etckeeper not complain when invoked by cron
+- git_config: name=user.email repo=/etc scope=local value="root@{{ ansible_fqdn }}"
+
+# Read individual values from git config
+- git_config: name=alias.ci scope=global
+# scope=system is also assumed when reading values, unless list_all=yes
+- git_config: name=alias.diffc
+
+# Read all values from git config
+- git_config: list_all=yes scope=global
+# When list_all=yes and no scope is specified, you get configuration from all scopes
+- git_config: list_all=yes
+# Specify a repository to include local settings
+- git_config: list_all=yes repo=/path/to/repo.git
+'''
+
+RETURN = '''
+---
+config_value:
+  description: When list_all=no and value is not set, a string containing the value of the setting in name
+  returned: success
+  type: string
+  sample: "vim"
+
+config_values:
+  description: When list_all=yes, a dict containing key/value pairs of multiple configuration settings
+  returned: success
+  type: dictionary
+  sample:
+    core.editor: "vim"
+    color.ui: "auto"
+    alias.diffc: "diff --cached"
+    alias.remotev: "remote -v"
+'''
+
+
+def main():
+    module = AnsibleModule(
+        argument_spec=dict(
+            list_all=dict(required=False, type='bool', default=False),
+            name=dict(type='str'),
+            repo=dict(type='path'),
+            scope=dict(required=False, type='str', choices=['local', 'global', 'system']),
+            value=dict(required=False)
+        ),
+        mutually_exclusive=[['list_all', 'name'], ['list_all', 'value']],
+        required_if=[('scope', 'local', ['repo'])],
+        required_one_of=[['list_all', 'name']],
+        supports_check_mode=True,
+    )
+    git_path = module.get_bin_path('git')
+    if not git_path:
+        module.fail_json(msg="Could not find git. Please ensure it is installed.")
+
+    params = module.params
+    # We check error message for a pattern, so we need to make sure the messages appear in the form we're expecting.
+    # Set the locale to C to ensure consistent messages.
+    module.run_command_environ_update = dict(LANG='C', LC_ALL='C', LC_MESSAGES='C', LC_CTYPE='C')
+
+    if params['name']:
+        name = params['name']
+    else:
+        name = None
+
+    if params['scope']:
+        scope = params['scope']
+    elif params['list_all']:
+        scope = None
+    else:
+        scope = 'system'
+
+    if params['value']:
+        new_value = params['value']
+    else:
+        new_value = None
+
+    args = [git_path, "config"]
+    if params['list_all']:
+        args.append('-l')
+    if scope:
+        args.append("--" + scope)
+    if name:
+        args.append(name)
+
+    if scope == 'local':
+        dir = params['repo']
+    elif params['list_all'] and params['repo']:
+        # Include local settings from a specific repo when listing all available settings
+        dir = params['repo']
+    else:
+        # Run from root directory to avoid accidentally picking up any local config settings
+        dir = "/"
+
+    (rc, out, err) = module.run_command(' '.join(args), cwd=dir)
+    if params['list_all'] and scope and rc == 128 and 'unable to read config file' in err:
+        # This just means nothing has been set at the given scope
+        module.exit_json(changed=False, msg='', config_values={})
+    elif rc >= 2:
+        # If the return code is 1, it just means the option hasn't been set yet, which is fine.
+        module.fail_json(rc=rc, msg=err, cmd=' '.join(args))
+
+    if params['list_all']:
+        values = out.rstrip().splitlines()
+        config_values = {}
+        for value in values:
+            k, v = value.split('=', 1)
+            config_values[k] = v
+        module.exit_json(changed=False, msg='', config_values=config_values)
+    elif not new_value:
+        module.exit_json(changed=False, msg='', config_value=out.rstrip())
+    else:
+        old_value = out.rstrip()
+        if old_value == new_value:
+            module.exit_json(changed=False, msg="")
+
+    if not module.check_mode:
+        new_value_quoted = "'" + new_value + "'"
+        (rc, out, err) = module.run_command(' '.join(args + [new_value_quoted]), cwd=dir)
+        if err:
+            module.fail_json(rc=rc, msg=err, cmd=' '.join(args + [new_value_quoted]))
+    module.exit_json(
+        msg='setting changed',
+        diff=dict(
+            before_header=' '.join(args),
+            before=old_value + "\n",
+            after_header=' '.join(args),
+            after=new_value + "\n"
+        ),
+        changed=True
+    )
+
+from ansible.module_utils.basic import *
+
+if __name__ == '__main__':
+    main()