Serialize Checkers PluginTypeManager to a dict

It seems likely that the multiprocessing module on Windows is not
capable of serializing an object with the structure that we have and
preserving the attributes we dynamically set on plugins (like the
FlakesChecker). To avoid issues like this with all plugins (although
we have only found this on Windows with the FlakesChecker), let's try
serializing the Checkers PluginTypeManager to a dictionary so that the
only object that a Queue is really trying to serialize/deserialize is
the FlakesChecker itself.

Related to #179

1 files changed, 24 insertions, 0 deletions

diff --git a/src/flake8/plugins/manager.py b/src/flake8/plugins/manager.py
index 28f38a6..a5f1c3b 100644
--- a/src/flake8/plugins/manager.py
+++ b/src/flake8/plugins/manager.py
@@ -49,6 +49,16 @@ class Plugin(object):
             self.name, self.entry_point
         )
 
+    def to_dictionary(self):
+        """Convert this plugin to a dictionary."""
+        return {
+            'name': self.name,
+            'parameters': self.parameters,
+            'parameter_names': self.parameter_names,
+            'plugin': self.plugin,
+            'plugin_name': self.plugin_name,
+        }
+
     def is_in_a_group(self):
         """Determine if this plugin is in a group.
 
@@ -433,6 +443,20 @@ class Checkers(PluginTypeManager):
             if argument_name == plugin.parameter_names[0]:
                 yield plugin
 
+    def to_dictionary(self):
+        """Return a dictionary of AST and line-based plugins."""
+        return {
+            'ast_plugins': [
+                plugin.to_dictionary() for plugin in self.ast_plugins
+            ],
+            'logical_line_plugins': [
+                plugin.to_dictionary() for plugin in self.logical_line_plugins
+            ],
+            'physical_line_plugins': [
+                plugin.to_dictionary() for plugin in self.physical_line_plugins
+            ],
+        }
+
     def register_options(self, optmanager):
         """Register all of the checkers' options to the OptionManager.