Added tests, adjusted warning message, and fixed the line in PyrexTypes.

Cython/Compiler/ExprNodes.py

@@ -11379,7 +11379,8 @@ class CoerceFromPyTypeNode(CoercionNode):
                   "Cannot convert Python object to '%s'" % result_type)
         elif result_type.is_reference:
             warning(arg.pos,
-                    "Cannot pass Python object as %s reference, will pass by copy." % result_type,
+                    "Cannot pass Python object as C++ data structure "
+                    "reference (%s &), will pass by copy." % result_type,
                     level=1)
         if self.type.is_string or self.type.is_pyunicode_ptr:
             if self.arg.is_name and self.arg.entry and self.arg.entry.is_pyglobal:

Cython/Compiler/PyrexTypes.py

@@ -3373,7 +3373,7 @@ class CppClassType(CType):
             return self
         if self.templates is None:
             self.templates = []
-        key = tuple(values.items() + [is_reference]) # Python 3?
+        key = tuple(values.items()) + (is_reference,)
         if key in self.specializations:
             return self.specializations[key]
         template_values = [t.specialize(values) for t in self.templates]

tests/errors/w_numpy_arr_as_cppvec_ref.pyx

+# mode: error
+# tag: werror
+
+import numpy as np
+cimport numpy as np
+from libcpp.vector cimport vector
+
+cdef extern from *:
+    void cpp_function_vector1(vector[int])
+    void cpp_function_vector2(vector[int] &)
+    void cpp_function_2_vec_refs(vector[int] &, vector[int] &)
+
+
+def main():
+    cdef np.ndarray[int, ndim=1, mode="c"] arr = np.zeros(10, dtype='intc')
+    cpp_function_vector1(arr)
+    cpp_function_vector2(arr)
+    cpp_function_vector2(arr)
+    cpp_function_2_vec_refs(arr, arr)
+
+    cdef vector[int] vec
+    vec.push_back(0)
+    cpp_function_vector2(vec)
+
+
+_ERRORS = """
+17:28: Cannot pass Python object as C++ data structure reference (vector[int] &), will pass by copy.
+18:28: Cannot pass Python object as C++ data structure reference (vector[int] &), will pass by copy.
+19:31: Cannot pass Python object as C++ data structure reference (vector[int] &), will pass by copy.
+19:36: Cannot pass Python object as C++ data structure reference (vector[int] &), will pass by copy.
+31:15: '<init>' redeclared
+31:15: '<init>' redeclared
+32:15: '<init>' redeclared
+32:15: '<init>' redeclared
+32:15: '<init>' redeclared
+33:15: '<init>' redeclared
+33:15: '<init>' redeclared
+33:15: '<init>' redeclared
+34:15: '<init>' redeclared
+44:19: 'assign' redeclared
+44:19: 'assign' redeclared
+45:35: 'assign' redeclared
+55:22: 'erase' redeclared
+55:22: 'erase' redeclared
+56:22: 'erase' redeclared
+58:23: 'insert' redeclared
+58:23: 'insert' redeclared
+59:19: 'insert' redeclared
+59:19: 'insert' redeclared
+59:19: 'insert' redeclared
+60:19: 'insert' redeclared
+69:19: 'resize' redeclared
+69:19: 'resize' redeclared
+70:19: 'resize' redeclared
+"""

tests/errors/w_python_list_as_cppset_ref.pyx

+# mode: error
+# tag: werror
+
+from libcpp.set cimport set
+
+cdef extern from "foo.cpp":
+    void cpp_function_set1(set[int])
+    void cpp_function_set2(set[int] &)
+
+
+def pass_py_obj_as_cpp_cont_ref():
+    cdef list ordered_set = [0, 0, 0, 0, 0]
+    cpp_function_set1(ordered_set)
+    cpp_function_set2(ordered_set)
+
+
+_ERRORS = """
+5:13: '<init>' redeclared
+5:13: '<init>' redeclared
+6:13: '<init>' redeclared
+6:13: '<init>' redeclared
+6:13: '<init>' redeclared
+6:13: '<init>' redeclared
+6:13: '<init>' redeclared
+7:13: '<init>' redeclared
+7:13: '<init>' redeclared
+7:13: '<init>' redeclared
+14:33: Cannot pass Python object as C++ data structure reference (set[int] &), will pass by copy.
+21:12: '<init>' redeclared
+21:12: '<init>' redeclared
+22:12: '<init>' redeclared
+40:18: 'erase' redeclared
+40:18: 'erase' redeclared
+41:18: 'erase' redeclared
+41:18: 'erase' redeclared
+41:18: 'erase' redeclared
+42:20: 'erase' redeclared
+45:35: 'insert' redeclared
+45:35: 'insert' redeclared
+46:23: 'insert' redeclared
+"""