object.__str__ use capi slot in order to increase compatibility with cpython

With this change we print True for:
class C(object):
    pass
print C.__str__ is object.__str__

Cheetah depends on this behaviour (see https://bitbucket.org/pypy/compatibility/wiki/cheetah)

src/runtime/descr.cpp

@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+#include "capi/typeobject.h"
 #include "codegen/compvars.h"
 #include "runtime/objmodel.h"
 #include "runtime/rewrite_args.h"
@@ -416,26 +417,13 @@ void BoxedMethodDescriptor::gcHandler(GCVisitor* v, Box* _o) {
     v->visit(o->type);
 }
 
-Box* BoxedWrapperDescriptor::__get__(BoxedWrapperDescriptor* self, Box* inst, Box* owner) {
-    STAT_TIMER(t0, "us_timer_boxedwrapperdescriptor_get", 20);
-
-    RELEASE_ASSERT(self->cls == wrapperdescr_cls, "");
-
-    if (inst == None)
-        return self;
-
-    if (!isSubclass(inst->cls, self->type))
-        raiseExcHelper(TypeError, "Descriptor '' for '%s' objects doesn't apply to '%s' object",
-                       getFullNameOfClass(self->type).c_str(), getFullTypeName(inst).c_str());
-
-    return new BoxedWrapperObject(self, inst);
-}
-
 Box* BoxedWrapperDescriptor::descr_get(Box* _self, Box* inst, Box* owner) noexcept {
+    STAT_TIMER(t0, "us_timer_boxedwrapperdescriptor_descr_get", 20);
+
     RELEASE_ASSERT(_self->cls == wrapperdescr_cls, "");
     BoxedWrapperDescriptor* self = static_cast<BoxedWrapperDescriptor*>(_self);
 
-    if (inst == None)
+    if (inst == NULL)
         return self;
 
     if (!isSubclass(inst->cls, self->type)) {
@@ -633,14 +621,14 @@ void setupDescr() {
     method_cls->giveAttr("__doc__", new (pyston_getset_cls) BoxedGetsetDescriptor(methodGetDoc, NULL, NULL));
     method_cls->freeze();
 
-    wrapperdescr_cls->giveAttr("__get__",
-                               new BoxedFunction(boxRTFunction((void*)BoxedWrapperDescriptor::__get__, UNKNOWN, 3)));
     wrapperdescr_cls->giveAttr("__call__", new BoxedFunction(boxRTFunction((void*)BoxedWrapperDescriptor::__call__,
                                                                            UNKNOWN, 2, 0, true, true)));
     wrapperdescr_cls->giveAttr("__doc__",
                                new (pyston_getset_cls) BoxedGetsetDescriptor(wrapperdescrGetDoc, NULL, NULL));
-    wrapperdescr_cls->freeze();
     wrapperdescr_cls->tp_descr_get = BoxedWrapperDescriptor::descr_get;
+    add_operators(wrapperdescr_cls);
+    wrapperdescr_cls->freeze();
+    assert(wrapperdescr_cls->tp_descr_get == BoxedWrapperDescriptor::descr_get);
 
     wrapperobject_cls->giveAttr(
         "__call__", new BoxedFunction(boxRTFunction((void*)BoxedWrapperObject::__call__, UNKNOWN, 1, 0, true, true)));

src/runtime/objmodel.cpp

@@ -1118,12 +1118,12 @@ Box* nondataDescriptorInstanceSpecialCases(GetattrRewriteArgs* rewrite_args, Box
         Box* inst = obj;
         Box* owner = obj->cls;
 
-        Box* r = BoxedWrapperDescriptor::__get__(self, inst, owner);
+        Box* r = BoxedWrapperDescriptor::descr_get(self, inst, owner);
 
         if (rewrite_args) {
             // TODO: inline this?
             RewriterVar* r_rtn = rewrite_args->rewriter->call(
-                /* has_side_effects= */ false, (void*)&BoxedWrapperDescriptor::__get__, r_descr, rewrite_args->obj,
+                /* has_side_effects= */ false, (void*)&BoxedWrapperDescriptor::descr_get, r_descr, rewrite_args->obj,
                 r_descr->getAttr(offsetof(Box, cls), Location::forArg(2)));
 
             rewrite_args->out_success = true;

src/runtime/types.cpp

@@ -2506,8 +2506,13 @@ Box* objectRepr(Box* obj) {
     return boxString(buf);
 }
 
-Box* objectStr(Box* obj) {
-    return obj->reprIC();
+static Box* object_str(Box* obj) noexcept {
+    try {
+        return obj->reprIC();
+    } catch (ExcInfo e) {
+        setCAPIException(e);
+        return NULL;
+    }
 }
 
 Box* objectHash(Box* obj) {
@@ -3449,7 +3454,6 @@ void setupRuntime() {
     FROZENSET = typeFromClass(frozenset_cls);
 
     object_cls->giveAttr("__repr__", new BoxedFunction(boxRTFunction((void*)objectRepr, UNKNOWN, 1, 0, false, false)));
-    object_cls->giveAttr("__str__", new BoxedFunction(boxRTFunction((void*)objectStr, UNKNOWN, 1, 0, false, false)));
     object_cls->giveAttr("__subclasshook__",
                          boxInstanceMethod(object_cls,
                                            new BoxedFunction(boxRTFunction((void*)objectSubclasshook, UNKNOWN, 2)),
@@ -3502,9 +3506,15 @@ void setupRuntime() {
         object_cls->giveAttr(md.ml_name, new BoxedMethodDescriptor(&md, object_cls));
     }
     object_cls->giveAttr("__class__", new (pyston_getset_cls) BoxedGetsetDescriptor(objectClass, objectSetClass, NULL));
+
+    object_cls->tp_str = object_str;
+    add_operators(object_cls);
+
     object_cls->freeze();
+
     assert(object_cls->tp_init == object_init);
     assert(object_cls->tp_new == object_new);
+    assert(object_cls->tp_str == object_str);
 
     setupBool();
     setupLong();

src/runtime/types.h

@@ -945,7 +945,6 @@ public:
 
     DEFAULT_CLASS(wrapperdescr_cls);
 
-    static Box* __get__(BoxedWrapperDescriptor* self, Box* inst, Box* owner);
     static Box* descr_get(Box* self, Box* inst, Box* owner) noexcept;
     static Box* __call__(BoxedWrapperDescriptor* descr, PyObject* self, BoxedTuple* args, Box** _args);
 

test/tests/wrapperdesc.py

+class C(object):
+    pass
+print C.__str__ is object.__str__
+print type(C).__str__ is object.__str__
+print type(None).__str__ is object.__str__
+print type(None).__str__ is None.__str__
+print type(None.__str__)
+print type(type(None).__str__.__get__(None, type(None)))

testsuite @ e1d16ce8

-Subproject commit 56631b487c6bfa7ccd9525cba2a27baff9b6b491
+Subproject commit e1d16ce8922700ef6bde50589e84db3a5c095c2b