Fix comparison of templates when mixing "const" with typedefs.

See #2148.

CHANGES.rst

@@ -14,6 +14,10 @@ Bugs fixed
 * ``PyFrozenSet_New()`` was accidentally used in PyPy where it is lacking
   from the C-API.
 
+* Assignment between some C++ templated types were incorrectly rejected
+  when the templates mix ``const`` with ``ctypedef``.
+  (Github issue #2148)
+
 
 0.28 (2018-03-13)
 =================

Cython/Compiler/PyrexTypes.py

@@ -1595,6 +1595,12 @@ class CConstType(BaseType):
             self.to_py_function = self.const_base_type.to_py_function
             return True
 
+    def same_as_resolved_type(self, other_type):
+        if other_type.is_const:
+            return self.const_base_type.same_as_resolved_type(other_type.const_base_type)
+        # Accept const LHS <- non-const RHS.
+        return self.const_base_type.same_as_resolved_type(other_type)
+
     def __getattr__(self, name):
         return getattr(self.const_base_type, name)
 

tests/run/cpp_smart_ptr.pyx

-# distutils: extra_compile_args=-std=c++0x
 # mode: run
-# tag: cpp, werror
+# tag: cpp, werror, cpp11
+# distutils: extra_compile_args=-std=c++0x
 
 from libcpp.memory cimport unique_ptr, shared_ptr, default_delete
 from libcpp cimport nullptr
@@ -12,6 +12,10 @@ cdef extern from "cpp_smart_ptr_helper.h":
     cdef cppclass FreePtr[T]:
         pass
 
+
+ctypedef const CountAllocDealloc const_CountAllocDealloc
+
+
 def test_unique_ptr():
     """
     >>> test_unique_ptr()
@@ -42,17 +46,18 @@ def test_unique_ptr():
     x_ptr3.reset()
     assert x_ptr3.get() == nullptr;
 
-def test_shared_ptr():
+
+def test_const_shared_ptr():
     """
-    >>> test_shared_ptr()
+    >>> test_const_shared_ptr()
     """
     cdef int alloc_count = 0, dealloc_count = 0
-    cdef shared_ptr[CountAllocDealloc] ptr = shared_ptr[CountAllocDealloc](
+    cdef shared_ptr[const CountAllocDealloc] ptr = shared_ptr[const_CountAllocDealloc](
         new CountAllocDealloc(&alloc_count, &dealloc_count))
     assert alloc_count == 1
     assert dealloc_count == 0
 
-    cdef shared_ptr[CountAllocDealloc] ptr2 = ptr
+    cdef shared_ptr[const CountAllocDealloc] ptr2 = ptr
     assert alloc_count == 1
     assert dealloc_count == 0