Fix inference cycle in getattr when a base is an astroid.Attribute

ChangeLog

@@ -41,6 +41,10 @@ Release Date: TBA
 
   Closes #922
 
+* Fix inference of attributes defined in a base class that is an inner class
+
+  Closes #904
+
 
 What's New in astroid 2.5.6?
 ============================

astroid/inference.py

@@ -309,6 +309,7 @@ def infer_attribute(self, context=None):
         elif not context:
             context = contextmod.InferenceContext()
 
+        old_boundnode = context.boundnode
         try:
             context.boundnode = owner
             yield from owner.igetattr(self.attrname, context)
@@ -319,7 +320,7 @@ def infer_attribute(self, context=None):
         ):
             pass
         finally:
-            context.boundnode = None
+            context.boundnode = old_boundnode
     return dict(node=self, context=context)
 
 

tests/unittest_inference.py

@@ -3894,6 +3894,65 @@ class Clazz(metaclass=_Meta):
         ).inferred()[0]
         assert isinstance(cls, nodes.ClassDef) and cls.name == "Clazz"
 
+    def test_infer_subclass_attr_outer_class(self):
+        node = extract_node(
+            """
+        class Outer:
+            data = 123
+
+        class Test(Outer):
+            pass
+        Test.data
+        """
+        )
+        inferred = next(node.infer())
+        assert isinstance(inferred, nodes.Const)
+        assert inferred.value == 123
+
+    def test_infer_subclass_attr_inner_class_works_indirectly(self):
+        node = extract_node(
+            """
+        class Outer:
+            class Inner:
+                data = 123
+        Inner = Outer.Inner
+
+        class Test(Inner):
+            pass
+        Test.data
+        """
+        )
+        inferred = next(node.infer())
+        assert isinstance(inferred, nodes.Const)
+        assert inferred.value == 123
+
+    def test_infer_subclass_attr_inner_class(self):
+        clsdef_node, attr_node = extract_node(
+            """
+        class Outer:
+            class Inner:
+                data = 123
+
+        class Test(Outer.Inner):
+            pass
+        Test  #@
+        Test.data  #@
+            """
+        )
+        clsdef = next(clsdef_node.infer())
+        assert isinstance(clsdef, nodes.ClassDef)
+        inferred = next(clsdef.igetattr("data"))
+        assert isinstance(inferred, nodes.Const)
+        assert inferred.value == 123
+        # Inferring the value of .data via igetattr() worked before the
+        # old_boundnode fixes in infer_subscript, so it should have been
+        # possible to infer the subscript directly. It is the difference
+        # between these two cases that led to the discovery of the cause of the
+        # bug in https://github.com/PyCQA/astroid/issues/904
+        inferred = next(attr_node.infer())
+        assert isinstance(inferred, nodes.Const)
+        assert inferred.value == 123
+
     def test_delayed_attributes_without_slots(self):
         ast_node = extract_node(
             """