application: Register preliminary options on a separate argument parser

We introduce a new `ArgumentParser` for registering the preliminary
options to be inherited by the `Application.option_manager`.  The next
step will be to use the `Application.prelim_arg_parser` for parsing and
handling preliminary options and arguments.

Note that we prevent the preliminary parser from handling `-h/--help`
and defer to that to the primary parser.

src/flake8/main/application.py

@@ -45,12 +45,17 @@ class Application(object):
         self.program = program
         #: The version of the program being run
         self.version = version
+        #: The prelimary argument parser for handling options required for
+        #: obtaining and parsing the configuration file.
+        self.prelim_arg_parser = argparse.ArgumentParser(add_help=False)
+        options.register_preliminary_options(self.prelim_arg_parser)
         #: 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(
-            prog="flake8", version=flake8.__version__
+            prog="flake8",
+            version=flake8.__version__,
+            parents=[self.prelim_arg_parser],
         )
-        options.register_preliminary_options(self.option_manager)
         options.register_default_options(self.option_manager)
         #: The instance of :class:`flake8.options.config.ConfigFileFinder`
         self.config_finder = None  # type: config.ConfigFileFinder

src/flake8/main/options.py

@@ -1,4 +1,5 @@
 """Contains the logic for all of the default options for Flake8."""
+import argparse
 import functools
 
 from flake8 import defaults
@@ -6,7 +7,8 @@ from flake8.main import debug
 from flake8.main import vcs
 
 
-def register_preliminary_options(option_manager):
+def register_preliminary_options(parser):
+    # type: (argparse.ArgumentParser) -> None
     """Register the preliminary options on our OptionManager.
 
     The preliminary options include:
@@ -17,9 +19,9 @@ def register_preliminary_options(option_manager):
     - ``--config``
     - ``--isolated``
     """
-    add_option = option_manager.add_option
+    add_argument = parser.add_argument
 
-    add_option(
+    add_argument(
         "-v",
         "--verbose",
         default=0,
@@ -29,13 +31,13 @@ def register_preliminary_options(option_manager):
         "time it is repeated.",
     )
 
-    add_option(
+    add_argument(
         "--output-file", default=None, help="Redirect report to a file."
     )
 
     # Config file options
 
-    add_option(
+    add_argument(
         "--append-config",
         action="append",
         help="Provide extra config files to parse in addition to the files "
@@ -44,7 +46,7 @@ def register_preliminary_options(option_manager):
         "provide the same option.",
     )
 
-    add_option(
+    add_argument(
         "--config",
         default=None,
         help="Path to the config file that will be the authoritative config "
@@ -52,7 +54,7 @@ def register_preliminary_options(option_manager):
         "configuration files.",
     )
 
-    add_option(
+    add_argument(
         "--isolated",
         default=False,
         action="store_true",

tests/integration/test_aggregator.py

@@ -1,4 +1,5 @@
 """Test aggregation of config files and command-line options."""
+import argparse
 import os
 
 import pytest
@@ -14,11 +15,13 @@ CLI_SPECIFIED_CONFIG = 'tests/fixtures/config_files/cli-specified.ini'
 @pytest.fixture
 def optmanager():
     """Create a new OptionManager."""
+    prelim_parser = argparse.ArgumentParser(add_help=False)
+    options.register_preliminary_options(prelim_parser)
     option_manager = manager.OptionManager(
         prog='flake8',
         version='3.0.0',
+        parents=[prelim_parser],
     )
-    options.register_preliminary_options(option_manager)
     options.register_default_options(option_manager)
     return option_manager