mypy now passes

src/flake8/formatting/default.py

@@ -1,6 +1,11 @@
 """Default formatting class for Flake8."""
+from typing import Optional, Set
+
 from flake8.formatting import base
 
+if False:  # `typing.TYPE_CHECKING` was introduced in 3.5.2
+    from flake8.style_guide import Violation
+
 
 class SimpleFormatter(base.BaseFormatter):
     """Simple abstraction for Default and Pylint formatter commonality.
@@ -18,9 +23,9 @@ class SimpleFormatter(base.BaseFormatter):
 
     """
 
-    error_format = None
+    error_format = None  # type: str
 
-    def format(self, error):
+    def format(self, error):  # type: (Violation) -> Optional[str]
         """Format and write error out.
 
         If an output filename is specified, write formatted errors to that
@@ -44,7 +49,7 @@ class Default(SimpleFormatter):
 
     error_format = "%(path)s:%(row)d:%(col)d: %(code)s %(text)s"
 
-    def after_init(self):
+    def after_init(self):  # type: () -> None
         """Check for a custom format string."""
         if self.options.format.lower() != "default":
             self.error_format = self.options.format
@@ -61,28 +66,27 @@ class FilenameOnly(SimpleFormatter):
 
     error_format = "%(path)s"
 
-    def after_init(self):
+    def after_init(self):  # type: () -> None
         """Initialize our set of filenames."""
-        self.filenames_already_printed = set()
+        self.filenames_already_printed = set()  # type: Set[str]
 
-    def show_source(self, error):
+    def show_source(self, error):  # type: (Violation) -> Optional[str]
         """Do not include the source code."""
-        pass
 
-    def format(self, error):
+    def format(self, error):  # type: (Violation) -> Optional[str]
         """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)
+        else:
+            return None
 
 
 class Nothing(base.BaseFormatter):
     """Print absolutely nothing."""
 
-    def format(self, error):
+    def format(self, error):  # type: (Violation) -> Optional[str]
         """Do nothing."""
-        pass
 
-    def show_source(self, error):
+    def show_source(self, error):  # type: (Violation) -> Optional[str]
         """Do not print the source."""
-        pass