Move git integration into flake8.main

Also add the --install-hook option and plumb it's installation through
flake8.main.vcs's function that understands how to install the desired
VCS integration bits.

Finally, we also mock out the mercurial integration.

flake8/main/cli.py

@@ -9,6 +9,7 @@ from flake8 import checker
 from flake8 import defaults
 from flake8 import style_guide
 from flake8 import utils
+from flake8.main import vcs
 from flake8.options import aggregator
 from flake8.options import manager
 from flake8.plugins import manager as plugin_manager
@@ -16,7 +17,7 @@ from flake8.plugins import manager as plugin_manager
 LOG = logging.getLogger(__name__)
 
 
-def register_default_options(option_manager):
+def register_default_options(option_manager, formatters=None):
     """Register the default options on our OptionManager.
 
     The default options include:
@@ -97,7 +98,7 @@ def register_default_options(option_manager):
 
     add_option(
         '--format', metavar='format', default='default',
-        parse_from_config=True,
+        parse_from_config=True, choices=(formatters or []),
         help='Format errors according to the chosen formatter.',
     )
 
@@ -160,6 +161,13 @@ def register_default_options(option_manager):
         help='Exit with status code "0" even if there are errors.',
     )
 
+    add_option(
+        '--install-hook', action='callback', type='string',
+        choices=vcs.choices(), callback=vcs.install,
+        help='Install a hook that is run prior to a commit for the supported '
+             'version control systema.'
+    )
+
     add_option(
         '-j', '--jobs', type='string', default='auto', parse_from_config=True,
         help='Number of subprocesses to use to run checks in parallel. '
@@ -215,10 +223,11 @@ class Application(object):
         self.version = version
         #: The instance of :class:`flake8.options.manager.OptionManager` used
         #: to parse and handle the options and arguments passed by the user
-        self.option_manager = manager.OptionManager(
+        self.option_manager = None
+        temp_option_manager = manager.OptionManager(
             prog='flake8', version=flake8.__version__
         )
-        register_default_options(self.option_manager)
+        register_default_options(temp_option_manager)
 
         # We haven't found or registered our plugins yet, so let's defer
         # printing the version until we aggregate options from config files
@@ -242,7 +251,7 @@ class Application(object):
         except ValueError:
             pass
 
-        preliminary_opts, _ = self.option_manager.parse_args(args)
+        preliminary_opts, _ = temp_option_manager.parse_args(args)
         # Set the verbosity of the program
         flake8.configure_logging(preliminary_opts.verbose,
                                  preliminary_opts.output_file)
@@ -418,7 +427,12 @@ class Application(object):
         This finds the plugins, registers their options, and parses the
         command-line arguments.
         """
+        self.option_manager = manager.OptionManager(
+            prog='flake8', version=flake8.__version__
+        )
         self.find_plugins()
+        register_default_options(self.option_manager,
+                                 self.formatting_plugins.names)
         self.register_plugin_options()
         self.parse_configuration_and_cli(argv)
         self.make_formatter()

flake8/main/git.py

@@ -1,6 +1,7 @@
 """Module containing the main git hook interface and helpers.
 
 .. autofunction:: hook
+.. autofunction:: install
 
 """
 import contextlib
@@ -180,7 +181,7 @@ _HOOK_TEMPLATE = """#!/usr/bin/env python
 import os
 import sys
 
-from flake8.api import git
+from flake8.main import git
 
 if __name__ == '__main__':
     sys.exit(

flake8/main/mercurial.py

@@ -0,0 +1,16 @@
+"""Module containing the main mecurial hook interface and helpers.
+
+.. autofunction:: hook
+.. autofunction:: install
+
+"""
+
+__all__ = ('hook', 'install')
+
+
+def hook(lazy=False, strict=False):
+    pass
+
+
+def install():
+    pass

flake8/main/vcs.py

@@ -0,0 +1,27 @@
+"""Module containing some of the logic for our VCS installation logic."""
+from flake8.main import git
+from flake8.main import mercurial
+
+
+# NOTE(sigmavirus24): In the future, we may allow for VCS hooks to be defined
+# as plugins, e.g., adding a flake8.vcs entry-point. In that case, this
+# dictionary should disappear, and this module might contain more code for
+# managing those bits (in conjuntion with flake8.plugins.manager).
+_INSTALLERS = {
+    'git': git.install,
+    'mercurial': mercurial.install,
+}
+
+
+def install(option, option_string, value, parser):
+    """Determine which version control hook to install.
+
+    For more information about the callback signature, see:
+    https://docs.python.org/2/library/optparse.html#optparse-option-callbacks
+    """
+    installer = _INSTALLERS.get(value)
+    installer()
+
+
+def choices():
+    return _INSTALLERS.keys()