Handle repeated --quiet options again

Fundamentally on Flake8 2.x using -q altered the format of the errors
(and the behaviour a little) so it makes the most sense to implement
this logic with formatters rather than messy logic spread throughout
the project.

The FilenameOnly formatter will keep track of filenames already reported
and only print the name once while Nothing will print nothing.

Closes #180

setup.py

@@ -107,6 +107,8 @@ setuptools.setup(
         'flake8.report': [
             'default = flake8.formatting.default:Default',
             'pylint = flake8.formatting.default:Pylint',
+            'quiet-filename = flake8.formatting.default:FilenameOnly',
+            'quiet-nothing = flake8.formatting.default:Nothing',
         ],
     },
     classifiers=[

src/flake8/formatting/base.py

@@ -164,7 +164,8 @@ class BaseFormatter(object):
             The source code that has been formatted and associated with the
             line of output.
         """
-        self._write(line)
+        if line:
+            self._write(line)
         if source:
             self._write(source)
 

src/flake8/formatting/default.py

@@ -54,3 +54,27 @@ class Pylint(SimpleFormatter):
     """Pylint formatter for Flake8."""
 
     error_format = '%(path)s:%(row)d: [%(code)s] %(text)s'
+
+
+class FilenameOnly(SimpleFormatter):
+    """Only print filenames, e.g., flake8 -q."""
+
+    error_format = '%(path)s'
+
+    def after_init(self):
+        """Initialize our set of filenames."""
+        self.filenames_already_printed = set()
+
+    def format(self, error):
+        """Ensure we only print each error once."""
+        if error.filename not in self.filenames_already_printed:
+            self.filenames_already_printed.add(error.filename)
+            return super(FilenameOnly, self).format(error)
+
+
+class Nothing(base.BaseFormatter):
+    """Print absolutely nothing."""
+
+    def format(self, error):
+        """Do nothing."""
+        pass

src/flake8/main/application.py

@@ -181,10 +181,17 @@ class Application(object):
         # type: () -> NoneType
         """Initialize a formatter based on the parsed options."""
         if self.formatter is None:
+            format_plugin = self.options.format
+            if 1 <= self.options.quiet < 2:
+                format_plugin = 'quiet-filename'
+            elif 2 <= self.options.quiet:
+                format_plugin = 'quiet-nothing'
+
             if formatter_class is None:
                 formatter_class = self.formatting_plugins.get(
-                    self.options.format, self.formatting_plugins['default']
+                    format_plugin, self.formatting_plugins['default']
                 ).execute
+
             self.formatter = formatter_class(self.options)
 
     def make_notifier(self):