Proper abstract method lookup while checking for abstract-class-instantiated.

This depends on the new Class.mro method, which will be added in astroid 1.3.3.
Closes issue #401.

4 files changed, 88 insertions, 5 deletions

diff --git a/ChangeLog b/ChangeLog
index d25a775..6e13e04 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -11,6 +11,9 @@ ChangeLog for Pylint
     * Warn about using the input() or round() built-ins for Python 3.
       Closes issue #411.
 
+    * Proper abstract method lookup while checking for
+      abstract-class-instantiated. Closes issue #401.
+
 
 2014-11-23 -- 1.4.0
 
diff --git a/checkers/base.py b/checkers/base.py
index 17e6713..60bc096 100644
--- a/checkers/base.py
+++ b/checkers/base.py
@@ -197,8 +197,37 @@ def _has_abstract_methods(node):
     Determine if the given `node` has
     abstract methods, defined with `abc` module.
     """
-    return any(_decorated_with_abc(meth)
-               for meth in node.methods())
+    visited = set()
+    try:
+        mro = reversed(node.mro())
+    except NotImplementedError:
+        # Old style class, it will not have a mro.
+        return False
+    for ancestor in mro:
+        for obj in ancestor.values():
+            infered = obj
+            if isinstance(obj, astroid.AssName):
+                infered = safe_infer(obj)
+                if not infered:
+                    continue
+                if not isinstance(infered, astroid.Function):
+                    if obj.name in visited:
+                        visited.remove(obj.name)
+            if isinstance(infered, astroid.Function):
+                # It's critical to use the original name,
+                # since after inferring, an object can be something
+                # else than expected, as in the case of the
+                # following assignment.
+                #
+                # class A:
+                #     def keys(self): pass
+                #     __iter__ = keys
+                abstract = _decorated_with_abc(infered)
+                if abstract:
+                    visited.add(obj.name)
+                elif not abstract and obj.name in visited:
+                    visited.remove(obj.name)
+    return len(visited) > 0
 
 def report_by_type_stats(sect, stats, old_stats):
     """make a report of
diff --git a/test/functional/abstract_class_instantiated_py3.py b/test/functional/abstract_class_instantiated_py3.py
index 146666e..8d94733 100644
--- a/test/functional/abstract_class_instantiated_py3.py
+++ b/test/functional/abstract_class_instantiated_py3.py
@@ -10,6 +10,7 @@ abstract methods.
 __revision__ = 0
 
 import abc
+import weakref
 
 class GoodClass(object, metaclass=abc.ABCMeta):
     pass
@@ -38,11 +39,60 @@ class ThirdBadClass(SecondBadClass):
     pass
 
 
+class Structure(object, metaclass=abc.ABCMeta):
+    @abc.abstractmethod
+    def __iter__(self):
+        pass
+    @abc.abstractmethod
+    def __len__(self):
+        pass
+    @abc.abstractmethod
+    def __contains__(self):
+        pass
+    @abc.abstractmethod
+    def __hash__(self):
+        pass
+
+class Container(Structure):
+    def __contains__(self):
+        pass
+
+class Sizable(Structure):
+    def __len__(self):
+        pass
+
+class Hashable(Structure):
+    __hash__ = 42
+
+
+class Iterator(Structure):
+    def keys(self): # pylint: disable=no-self-use
+        return iter([1, 2, 3])
+
+    __iter__ = keys
+
+class AbstractSizable(Structure):
+    @abc.abstractmethod
+    def length(self):
+        pass
+    __len__ = length
+
+class NoMroAbstractMethods(Container, Iterator, Sizable, Hashable):
+    pass
+
+class BadMroAbstractMethods(Container, Iterator, AbstractSizable):
+    pass
+
 def main():
     """ do nothing """
     GoodClass()
     SecondGoodClass()
     ThirdGoodClass()
+    weakref.WeakKeyDictionary()
+    weakref.WeakValueDictionary()
+    NoMroAbstractMethods()
+
+    BadMroAbstractMethods() # [abstract-class-instantiated]
     BadClass() # [abstract-class-instantiated]
     SecondBadClass() # [abstract-class-instantiated]
     ThirdBadClass() # [abstract-class-instantiated]
diff --git a/test/functional/abstract_class_instantiated_py3.txt b/test/functional/abstract_class_instantiated_py3.txt
index 3c4f0c2..db5bef6 100644
--- a/test/functional/abstract_class_instantiated_py3.txt
+++ b/test/functional/abstract_class_instantiated_py3.txt
@@ -1,3 +1,4 @@
-abstract-class-instantiated:46:main:Abstract class with abstract methods instantiated

-abstract-class-instantiated:47:main:Abstract class with abstract methods instantiated

-abstract-class-instantiated:48:main:Abstract class with abstract methods instantiated
\ No newline at end of file
+abstract-class-instantiated:95:main:Abstract class with abstract methods instantiated

+abstract-class-instantiated:96:main:Abstract class with abstract methods instantiated

+abstract-class-instantiated:97:main:Abstract class with abstract methods instantiated

+abstract-class-instantiated:98:main:Abstract class with abstract methods instantiated