Fix logic for Notifier.listeners_for

Add tests for proper logic around notifier

DESIGN.rst

@@ -77,6 +77,18 @@ See https://gitlab.com/pycqa/flake8/issues/84
 
 .. note:: Will probably need a Trie implementation for this
 
+What we *might* want is for a autofix plugin to register something like
+
+::
+
+    'flake8.autofix_extension': [
+        'E1 = my_fixer.E1Listener',
+        'E2 = my_fixer.E2Listener',
+    ]
+
+This means that the notifer would need to take an error code like ``E111`` and
+then notify anything listening for ``E111``, ``E11``, ``E1``, and ``E``.
+
 .. _reporter-plugins:
 
 Support for Plugins that Format Output

flake8/notifier.py

@@ -9,12 +9,12 @@ class Notifier(object):
     def listeners_for(self, error_code):
         """Retrieve listeners for an error_code.
 
-        The error code does not need to be a specific error code. For example,
-        There may be listeners registered for E100, E101, E110, E112, and
-        E126. If you wanted to get all listeners starting with 'E1' then you
-        would pass 'E1' as the error code here.
+        There may be listeners registered for E1, E100, E101, E110, E112, and
+        E126. To get all the listeners for one of E100, E101, E110, E112, or
+        E126 you would also need to incorporate the listeners for E1 (since
+        they're all in the same class).
 
-        Example usage
+        Example usage:
 
         .. code-block:: python
 
@@ -22,20 +22,15 @@ class Notifier(object):
 
             n = notifier.Notifier()
             # register listeners
-            for listener in n.listeners_for('E1'):
-                listener.notify(...)
-
             for listener in n.listeners_for('W102'):
                 listener.notify(...)
         """
-        node = self.listeners.find(error_code)
-        if node is None:
-            return
-        for listener in node.data:
-            yield listener
-        for child in node.traverse():
-            for listener in child.data:
+        path = error_code
+        while path:
+            node = self.listeners.find(path)
+            for listener in node.data:
                 yield listener
+            path = path[:-1]
 
     def notify(self, error_code, *args, **kwargs):
         """Notify all listeners for the specified error code."""

tests/test_notifier.py

@@ -8,7 +8,7 @@ class _Listener(object):
         self.was_notified = False
 
     def notify(self, error_code, *args, **kwargs):
-        assert self.error_code == error_code
+        assert error_code.startswith(self.error_code)
         self.was_notified = True
 
 
@@ -18,14 +18,18 @@ class TestNotifier(object):
         self.notifier = notifier.Notifier()
         self.listener_map = {}
 
-        for i in range(10):
-            for j in range(30):
-                error_code = 'E{0}{1:02d}'.format(i, j)
-                listener = _Listener(error_code)
-                self.listener_map[error_code] = listener
-                self.notifier.register_listener(error_code, listener)
+        def add_listener(error_code):
+            listener = _Listener(error_code)
+            self.listener_map[error_code] = listener
+            self.notifier.register_listener(error_code, listener)
 
-    def test_notify_a_single_error_code(self):
+        for i in range(10):
+            add_listener('E{0}'.format(i))
+            for j in range(30):
+                add_listener('E{0}{1:02d}'.format(i, j))
+
+    def test_notify(self):
         """Show that we notify a specific error code."""
         self.notifier.notify('E111', 'extra', 'args')
         assert self.listener_map['E111'].was_notified is True
+        assert self.listener_map['E1'].was_notified is True