Recognize __qualname__ when used in class scope (#588)

Relates #259.

pyflakes/checker.py

@@ -669,6 +669,10 @@ def __init__(self, lineno, col_offset):
         self.col_offset = col_offset
 
 
+class DetectClassScopedMagic:
+    names = dir()
+
+
 # Globally defined names which are not attributes of the builtins module, or
 # are only present on some platforms.
 _MAGIC_GLOBALS = ['__file__', '__builtins__', 'WindowsError']
@@ -1231,7 +1235,7 @@ def handleNodeLoad(self, node):
             # the special name __path__ is valid only in packages
             return
 
-        if name == '__module__' and isinstance(self.scope, ClassScope):
+        if name in DetectClassScopedMagic.names and isinstance(self.scope, ClassScope):
             return
 
         # protected with a NameError handler?

pyflakes/test/test_undefined_names.py

@@ -279,6 +279,23 @@ def bar(self):
                 __module__
         ''', m.UndefinedName)
 
+    @skipIf(version_info < (3, 3), "Python >= 3.3 only")
+    def test_magicQualnameInClassScope(self):
+        """
+        Use of the C{__qualname__} magic builtin should not emit an undefined
+        name warning if used in class scope.
+        """
+        self.flakes('__qualname__', m.UndefinedName)
+        self.flakes('''
+        class Foo:
+            __qualname__
+        ''')
+        self.flakes('''
+        class Foo:
+            def bar(self):
+                __qualname__
+        ''', m.UndefinedName)
+
     def test_globalImportStar(self):
         """Can't find undefined names with import *."""
         self.flakes('from fu import *; bar',