Refactor off-by-default plugins and enabling them

We move the logic to add or remove a plugin from the default ignore
list to individual methods on the Plugin class (Plugin#enable,
Plugin#disable) and use that when registering and parsing options.

If the plugin is off-by-default, Plugin#register_options will use
Plugin#disable. When parsing options via Plugin#provide_options, if
the plugin has been specified in --enable-extensions then it will be
re-enabled via Plugin#enable.

1 files changed, 12 insertions, 1 deletions

diff --git a/flake8/plugins/manager.py b/flake8/plugins/manager.py
index fe51391..dffc2f6 100644
--- a/flake8/plugins/manager.py
+++ b/flake8/plugins/manager.py
@@ -158,6 +158,14 @@ class Plugin(object):
                 LOG.critical(str(failed_to_load))
                 raise failed_to_load
 
+    def enable(self, optmanager):
+        """Remove plugin name from the default ignore list."""
+        optmanager.remove_from_default_ignore([self.name])
+
+    def disable(self, optmanager):
+        """Add the plugin name to the default ignore list."""
+        optmanager.extend_default_ignore([self.name])
+
     def provide_options(self, optmanager, options, extra_args):
         """Pass the parsed options and extra arguments to the plugin."""
         parse_options = getattr(self.plugin, 'parse_options', None)
@@ -168,6 +176,9 @@ class Plugin(object):
             except TypeError:
                 parse_options(options)
 
+        if self.name in options.enable_extensions:
+            self.enable(optmanager)
+
     def register_options(self, optmanager):
         """Register the plugin's command-line options on the OptionManager.
 
@@ -187,7 +198,7 @@ class Plugin(object):
             add_options(optmanager)
 
         if self.off_by_default:
-            optmanager.extend_default_ignore([self.name])
+            self.disable(optmanager)
 
 
 class PluginManager(object):  # pylint: disable=too-few-public-methods