non-iterator-returned can detect classes with iterator-metaclasses.

Closes issue #679.

4 files changed, 74 insertions, 18 deletions

diff --git a/ChangeLog b/ChangeLog
index 957ed56..8d6c9a7 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -2,6 +2,10 @@ ChangeLog for Pylint
 --------------------
 
 --
+
+    * non-iterator-returned can detect classes with iterator-metaclasses.
+      Closes issue #679.
+
     * Add a new error, 'unsupported-membership-test', emitted when value
       to the right of the 'in' operator doesn't support membership test
       protocol (i.e. doesn't define __contains__/__iter__/__getitem__)
diff --git a/pylint/checkers/classes.py b/pylint/checkers/classes.py
index c39b971..86ccb19 100644
--- a/pylint/checkers/classes.py
+++ b/pylint/checkers/classes.py
@@ -1006,23 +1006,39 @@ class SpecialMethodsChecker(BaseChecker):
                              args=(node.name, expected_params, current_params, verb),
                              node=node)
 
+    @staticmethod
+    def _is_iterator(node):
+        if node is astroid.YES:
+            # Just ignore YES objects.
+            return True
+        if isinstance(node, Generator):
+            # Generators can be itered.
+            return True
+
+        if isinstance(node, astroid.Instance):
+            try:
+                node.local_attr(NEXT_METHOD)
+                return True
+            except astroid.NotFoundError:
+                pass
+        elif isinstance(node, astroid.ClassDef):
+            metaclass = node.metaclass()
+            if metaclass and isinstance(metaclass, astroid.ClassDef):
+                try:
+                    metaclass.local_attr(NEXT_METHOD)
+                    return True
+                except astroid.NotFoundError:
+                    pass
+        return False
+
     def _check_iter(self, node):
         try:
             infered = node.infer_call_result(node)
         except astroid.InferenceError:
             return
 
-        for infered_node in infered:
-            if (infered_node is astroid.YES
-                    or isinstance(infered_node, Generator)):
-                continue
-            if isinstance(infered_node, astroid.Instance):
-                try:
-                    infered_node.local_attr(NEXT_METHOD)
-                except astroid.NotFoundError:
-                    self.add_message('non-iterator-returned',
-                                     node=node)
-                    break
+        if not all(map(self._is_iterator, infered)):
+            self.add_message('non-iterator-returned', node=node)
 
 
 def _ancestors_to_call(klass_node, method='__init__'):
diff --git a/pylint/test/functional/non_iterator_returned.py b/pylint/test/functional/non_iterator_returned.py
index 845500b..804ceee 100644
--- a/pylint/test/functional/non_iterator_returned.py
+++ b/pylint/test/functional/non_iterator_returned.py
@@ -1,8 +1,8 @@
 """Check non-iterators returned by __iter__ """
 
-# pylint: disable=too-few-public-methods
+# pylint: disable=too-few-public-methods, missing-docstring, no-self-use
 
-__revision__ = 0
+import six
 
 class FirstGoodIterator(object):
     """ yields in iterator. """
@@ -17,11 +17,11 @@ class SecondGoodIterator(object):
     def __iter__(self):
         return self
 
-    def __next__(self): # pylint: disable=no-self-use
+    def __next__(self):
         """ Infinite iterator, but still an iterator """
         return 1
 
-    def next(self): # pylint: disable=no-self-use
+    def next(self):
         """Same as __next__, but for Python 2."""
         return 1
 
@@ -37,6 +37,26 @@ class FourthGoodIterator(object):
     def __iter__(self):
         return iter(range(10))
 
+
+class IteratorMetaclass(type):
+    def __next__(cls):
+        return 1
+
+    def next(cls):
+        return 2
+
+
+@six.add_metaclass(IteratorMetaclass)
+class IteratorClass(object):
+    """Iterable through the metaclass."""
+
+
+class FifthGoodIterator(object):
+    """__iter__ returns a class which uses an iterator-metaclass."""
+    def __iter__(self):
+        return IteratorClass
+
+
 class FirstBadIterator(object):
     """ __iter__ returns a list """
 
@@ -54,3 +74,17 @@ class ThirdBadIterator(object):
 
     def __iter__(self): # [non-iterator-returned]
         return SecondBadIterator()
+
+class FourthBadIterator(object):
+    """__iter__ returns a class."""
+
+    def __iter__(self): # [non-iterator-returned]
+        return ThirdBadIterator
+
+class FifthBadIterator(object):
+    """All branches should return an iterator."""
+
+    def __iter__(self): # [non-iterator-returned]
+        if self:
+            return 1
+        return SecondGoodIterator()
diff --git a/pylint/test/functional/non_iterator_returned.txt b/pylint/test/functional/non_iterator_returned.txt
index f2881eb..fe3db10 100644
--- a/pylint/test/functional/non_iterator_returned.txt
+++ b/pylint/test/functional/non_iterator_returned.txt
@@ -1,3 +1,5 @@
-non-iterator-returned:43:FirstBadIterator.__iter__:__iter__ returns non-iterator
-non-iterator-returned:49:SecondBadIterator.__iter__:__iter__ returns non-iterator
-non-iterator-returned:55:ThirdBadIterator.__iter__:__iter__ returns non-iterator
\ No newline at end of file
+non-iterator-returned:63:FirstBadIterator.__iter__:__iter__ returns non-iterator
+non-iterator-returned:69:SecondBadIterator.__iter__:__iter__ returns non-iterator
+non-iterator-returned:75:ThirdBadIterator.__iter__:__iter__ returns non-iterator
+non-iterator-returned:81:FourthBadIterator.__iter__:__iter__ returns non-iterator
+non-iterator-returned:87:FifthBadIterator.__iter__:__iter__ returns non-iterator
\ No newline at end of file