Fix crash on unpacking with invalid base class (#2249)

gvanrossum · web-flow · commit c7ef72d8d0d2 · 2016-10-13T16:06:08.000-07:00
Fixes #2244.
diff --git a/mypy/maptype.py b/mypy/maptype.py
@@ -36,7 +36,11 @@ def map_instance_to_supertypes(instance: Instance,
                 a.extend(map_instance_to_direct_supertypes(t, sup))
             types = a
         result.extend(types)
-    return result
+    if result:
+        return result
+    else:
+        # Nothing. Presumably due to an error. Construct a dummy using Any.
+        return [Instance(supertype, [AnyType()] * len(supertype.type_vars))]
 
 
 def class_derivation_paths(typ: TypeInfo,
diff --git a/test-data/unit/check-classes.test b/test-data/unit/check-classes.test
@@ -1419,6 +1419,11 @@ C(0)
 C(arg=0)
 [out]
 
+[case testErrorMapToSupertype]
+import typing
+class X(Nope): pass  # E: Name 'Nope' is not defined
+a, b = X()  # Used to crash here (#2244)
+
 
 -- Type[C]
 -- -------
