Get func_arg_passing.py working

src/runtime/descr.cpp

@@ -834,7 +834,7 @@ void setupDescr() {
     property_cls->giveAttr("__init__", new BoxedFunction(FunctionMetadata::create(
                                                              (void*)propertyInit, UNKNOWN, 5, false, false,
                                                              ParamNames({ "", "fget", "fset", "fdel", "doc" }, "", "")),
-                                                         { NULL, NULL, NULL, NULL }));
+                                                         { None, None, None, NULL }));
     property_cls->giveAttr("__get__", new BoxedFunction(FunctionMetadata::create((void*)propertyGet, UNKNOWN, 3)));
     property_cls->giveAttr("__set__", new BoxedFunction(FunctionMetadata::create((void*)propertySet, UNKNOWN, 3)));
     property_cls->giveAttr("__delete__", new BoxedFunction(FunctionMetadata::create((void*)propertyDel, UNKNOWN, 2)));

src/runtime/objmodel.cpp

@@ -4229,7 +4229,6 @@ void rearrangeArgumentsInternal(ParamReceiveSpec paramspec, const ParamNames* pa
     }
 
     if (argspec.num_keywords) {
-        assert(!rewrite_args && "check refcounting");
         assert(argspec.num_keywords == keyword_names->size());
 
         RewriterVar::SmallVector r_vars;
@@ -4242,7 +4241,7 @@ void rearrangeArgumentsInternal(ParamReceiveSpec paramspec, const ParamNames* pa
                 if (i == 2)
                     r_vars.push_back(rewrite_args->arg3);
                 if (i >= 3)
-                    r_vars.push_back(rewrite_args->args->getAttr((i - 3) * sizeof(Box*)));
+                    r_vars.push_back(rewrite_args->args->getAttr((i - 3) * sizeof(Box*))->setType(RefType::BORROWED));
             }
         }
 

src/runtime/types.cpp

@@ -1630,7 +1630,7 @@ static void functionSetDefaults(Box* b, Box* v, void*) {
     BoxedTuple* t = static_cast<BoxedTuple*>(v);
 
     auto old_defaults = func->defaults;
-    func->defaults = incref(t);
+    func->defaults = xincref(t); // t can be NULL for 'del f.func_defaults'
     Py_XDECREF(old_defaults);
     func->dependent_ics.invalidateAll();
 }

test/tests/func_arg_passing.py

-# expected: reffail
 def f():
     def f1(a, b, c):
         print a, b, c
@@ -51,3 +50,7 @@ g()
 del f2.func_defaults
 g()
 g()
+
+def f4(a, b, c, d, e):
+    print a, b, c, d, e
+f4(a=1, b=2, c=3, d=4, e=5)