allow unprefixed 'str' literals in C varargs lists

CHANGES.rst

@@ -120,6 +120,8 @@ Bugs fixed
 * Some complex Python expressions could fail to compile inside of finally
   clauses.
 
+* Unprefixed 'str' literals were not supported as C varargs arguments.
+
 Other changes
 -------------
 

Cython/Compiler/ExprNodes.py

@@ -4799,7 +4799,10 @@ class SimpleCallNode(CallNode):
         for i in range(max_nargs, actual_nargs):
             arg = args[i]
             if arg.type.is_pyobject:
-                arg_ctype = arg.type.default_coerced_ctype()
+                if arg.type is str_type:
+                    arg_ctype = PyrexTypes.c_char_ptr_type
+                else:
+                    arg_ctype = arg.type.default_coerced_ctype()
                 if arg_ctype is None:
                     error(self.args[i].pos,
                           "Python object cannot be passed as a varargs parameter")

tests/run/varargcall.pyx

-cdef grail(char *blarg, ...):
+cdef grail(const char *blarg, ...):
     pass
 
+
 def swallow():
     """
     >>> swallow()
     """
     grail("spam")
     grail("spam", 42)
+    grail("spam", b"abc")
+    grail("spam", "abc")