application: Remove configuration finder state

This change removes the `.config_finder` object from the `Application`.
Since the configuration finder is only needed during initialization, we
constrain the finder to be returned and passed to other methods
necessary for initialization.

src/flake8/api/legacy.py

@@ -30,12 +30,14 @@ def get_style_guide(**kwargs):
     application = app.Application()
     prelim_opts, remaining_args = application.parse_preliminary_options([])
     flake8.configure_logging(prelim_opts.verbose, prelim_opts.output_file)
-    application.config_finder = application.make_config_finder(
+    config_finder = application.make_config_finder(
         application.program, prelim_opts.append_config
     )
-    application.find_plugins(prelim_opts.config, prelim_opts.isolated)
+    application.find_plugins(
+        config_finder, prelim_opts.config, prelim_opts.isolated
+    )
     application.register_plugin_options()
-    application.parse_configuration_and_cli(remaining_args)
+    application.parse_configuration_and_cli(config_finder, remaining_args)
     # We basically want application.initialize to be called but with these
     # options set instead before we make our formatter, notifier, internal
     # style guide and file checker manager.

src/flake8/main/application.py

@@ -57,8 +57,6 @@ class Application(object):
             parents=[self.prelim_arg_parser],
         )
         options.register_default_options(self.option_manager)
-        #: The instance of :class:`flake8.options.config.ConfigFileFinder`
-        self.config_finder = None  # type: config.ConfigFileFinder
 
         #: The :class:`flake8.options.config.LocalPlugins` found in config
         self.local_plugins = None  # type: config.LocalPlugins
@@ -150,8 +148,8 @@ class Application(object):
         """
         return config.ConfigFileFinder(program_name, extra_config_files)
 
-    def find_plugins(self, config_file, ignore_config_files):
-        # type: (Optional[str], bool) -> None
+    def find_plugins(self, config_finder, config_file, ignore_config_files):
+        # type: (config.ConfigFileFinder, Optional[str], bool) -> None
         """Find and load the plugins for this application.
 
         If :attr:`check_plugins`, or :attr:`formatting_plugins` are ``None``
@@ -160,6 +158,8 @@ class Application(object):
         we want this to be idempotent and so only update those attributes if
         they are ``None``.
 
+        :param config.ConfigFileFinder config_finder:
+            The finder for finding and reading configuration files.
         :param str config_file:
             The optional configuraiton file to override all other configuration
             files (i.e., the --config option).
@@ -168,7 +168,7 @@ class Application(object):
             --isolated option).
         """
         self.local_plugins = config.get_local_plugins(
-            self.config_finder, config_file, ignore_config_files
+            config_finder, config_file, ignore_config_files
         )
 
         sys.path.extend(self.local_plugins.paths)
@@ -191,15 +191,17 @@ class Application(object):
         self.check_plugins.register_plugin_versions(self.option_manager)
         self.formatting_plugins.register_options(self.option_manager)
 
-    def parse_configuration_and_cli(self, argv):
-        # type: (List[str]) -> None
+    def parse_configuration_and_cli(self, config_finder, argv):
+        # type: (config.ConfigFileFinder, List[str]) -> None
         """Parse configuration files and the CLI options.
 
+        :param config.ConfigFileFinder config_finder:
+            The finder for finding and reading configuration files.
         :param list argv:
             Command-line arguments passed in directly.
         """
         self.options, self.args = aggregator.aggregate_options(
-            self.option_manager, self.config_finder, argv
+            self.option_manager, config_finder, argv
         )
 
         self.running_against_diff = self.options.diff
@@ -338,12 +340,14 @@ class Application(object):
         # our legacy API calls to these same methods.
         prelim_opts, remaining_args = self.parse_preliminary_options(argv)
         flake8.configure_logging(prelim_opts.verbose, prelim_opts.output_file)
-        self.config_finder = self.make_config_finder(
+        config_finder = self.make_config_finder(
             self.program, prelim_opts.append_config
         )
-        self.find_plugins(prelim_opts.config, prelim_opts.isolated)
+        self.find_plugins(
+            config_finder, prelim_opts.config, prelim_opts.isolated
+        )
         self.register_plugin_options()
-        self.parse_configuration_and_cli(remaining_args)
+        self.parse_configuration_and_cli(config_finder, remaining_args)
         self.make_formatter()
         self.make_guide()
         self.make_file_checker_manager()

tests/unit/test_legacy_api.py

@@ -6,6 +6,7 @@ import pytest
 
 from flake8.api import legacy as api
 from flake8.formatting import base as formatter
+from flake8.options.config import ConfigFileFinder
 
 
 def test_get_style_guide():
@@ -20,6 +21,8 @@ def test_get_style_guide():
     mockedapp = mock.Mock()
     mockedapp.parse_preliminary_options.return_value = (prelim_opts, [])
     mockedapp.program = 'flake8'
+    config_finder = ConfigFileFinder(mockedapp.program, [])
+    mockedapp.make_config_finder.return_value = config_finder
     with mock.patch('flake8.main.application.Application') as application:
         application.return_value = mockedapp
         style_guide = api.get_style_guide()
@@ -27,9 +30,10 @@ def test_get_style_guide():
     application.assert_called_once_with()
     mockedapp.parse_preliminary_options.assert_called_once_with([])
     mockedapp.make_config_finder.assert_called_once_with(mockedapp.program, [])
-    mockedapp.find_plugins.assert_called_once_with(None, False)
+    mockedapp.find_plugins.assert_called_once_with(config_finder, None, False)
     mockedapp.register_plugin_options.assert_called_once_with()
-    mockedapp.parse_configuration_and_cli.assert_called_once_with([])
+    mockedapp.parse_configuration_and_cli.assert_called_once_with(
+        config_finder, [])
     mockedapp.make_formatter.assert_called_once_with()
     mockedapp.make_guide.assert_called_once_with()
     mockedapp.make_file_checker_manager.assert_called_once_with()