More complete test and fix for template specialization issues.

Partial workaround for Github Issue #1852.

Cython/Compiler/Nodes.py

@@ -1924,7 +1924,7 @@ class FuncDefNode(StatNode, BlockNode):
 
         code.mark_pos(self.pos, trace=False)
         code.putln("")
-        code.putln("/* function exit code */")
+        code.putln("/* function exit codeX */")
 
         # ----- Default return value
         if not self.body.is_terminator:

Cython/Compiler/PyrexTypes.py

@@ -3666,8 +3666,11 @@ class CppClassType(CType):
         if other_type.is_cpp_class:
             if self == other_type:
                 return 1
-            elif (self.cname == other_type.cname
-                  and (self.templates or other_type.templates)):
+            # This messy logic is needed due to GH Issue #1852.
+            elif (self.cname == other_type.cname and
+                  (self.template_type and other_type.template_type
+                   or self.templates
+                   or other_type.templates)):
                 if self.templates == other_type.templates:
                     return 1
                 for t1, t2 in zip(self.templates, other_type.templates):

tests/run/cpp_template_subclasses.pyx

@@ -125,3 +125,16 @@ def test_GH1599(a, b):
   (1, 2.0)
   """
   return public_return_pair(a, b)
+
+
+# Related to GH Issue #1852.
+
+cdef cppclass Callback[T]:#(UntypedCallback):
+    pass
+
+cdef cppclass MyClass[O]:
+    void Invoke(Callback[O]*)
+
+cdef cppclass MySubclass[T](MyClass[T]):
+    void Invoke(Callback[T]* callback):
+      pass