Correctly look up module of superclass.

Cython/Compiler/Nodes.py

@@ -4535,7 +4535,10 @@ class CClassDefNode(ClassDefNode):
 
         if self.base_class_name:
             if self.base_class_module:
-                base_class_scope = env.find_module(self.base_class_module, self.pos)
+                base_class_scope = env.find_imported_module(self.base_class_module.split('.'), self.pos)
+                if not base_class_scope:
+                    error(self.pos, "'%s' is not a cimported module" % self.base_class_module)
+                    return
             else:
                 base_class_scope = env
             if self.base_class_name == 'object':

tests/compile/cimported_class_base.srctree

+PYTHON setup.py build_ext --inplace
+
+######## setup.py ########
+
+from Cython.Build import cythonize
+from Cython.Distutils.extension import Extension
+
+import sys
+sys.path.append("path")
+
+ext_modules = [
+    Extension("importer", ["importer.pyx"]),
+]
+
+ext_modules = cythonize(ext_modules, include_path=["include"])
+
+
+######## pkg/__init__.py ########
+
+
+######## pkg/a.pxd ########
+
+cdef class A(object):
+  pass
+
+######## importer.pyx ########
+
+cimport pkg.a
+cimport pkg.a as a
+cimport pkg.a as a_by_another_name
+from pkg cimport a as from_cimported_a
+
+cdef class A1(a.A):
+  pass
+
+cdef class A2(a_by_another_name.A):
+  pass
+
+cdef class A3(pkg.a.A):
+  pass
+
+cdef class A4(from_cimported_a.A):
+  pass