Merge pull request #1728 from jdemeyer/call_one_arg_no_cyfunction

Don't use __Pyx_PyObject_CallMethO on cyfunctions

Cython/Utility/ObjectHandling.c

@@ -1686,11 +1686,7 @@ static CYTHON_INLINE PyObject* __Pyx_PyObject_CallOneArg(PyObject *func, PyObjec
         return __Pyx_PyFunction_FastCall(func, &arg, 1);
     }
 #endif
-#ifdef __Pyx_CyFunction_USED
-    if (likely(PyCFunction_Check(func) || PyObject_TypeCheck(func, __pyx_CyFunctionType))) {
-#else
     if (likely(PyCFunction_Check(func))) {
-#endif
         if (likely(PyCFunction_GET_FLAGS(func) & METH_O)) {
             // fast and simple case that we are optimising for
             return __Pyx_PyObject_CallMethO(func, arg);

tests/run/cyfunction_METH_O_GH1728.pyx

+# cython: binding=True
+# mode: run
+# tag: cyfunction
+
+cdef class TestMethodOneArg:
+    def meth(self, arg):
+        pass
+
+def call_meth(x):
+    """
+    >>> call_meth(TestMethodOneArg())
+    Traceback (most recent call last):
+    ...
+    TypeError: meth() takes exactly one argument (0 given)
+    """
+    return x.meth()