Fix some slot handling issues

Well, fix one of them and work around another.  They both come from having
an extension class subclass from a builtin class, since in CPython they can
expect the tp_* slots to be set, but in Pyston those are just wrappers around
the Python functions and then things can get in infinite recursion.

src/capi/typeobject.cpp

@@ -395,7 +395,9 @@ static PyObject* wrap_init(PyObject* self, PyObject* args, void* wrapped, PyObje
 static PyObject* lookup_maybe(PyObject* self, const char* attrstr, PyObject** attrobj) noexcept {
     PyObject* res;
 
-    // TODO: CPython uses the attrobj as a cache
+    // TODO: CPython uses the attrobj as a cache.  If we want to use it, we'd have to make sure that
+    // they get registered as GC roots since they are usually placed into static variables.
+
     Box* obj = typeLookup(self->cls, attrstr, NULL);
     if (obj)
         return processDescriptor(obj, self, self->cls);
@@ -1842,9 +1844,6 @@ extern "C" int PyType_Ready(PyTypeObject* cls) noexcept {
     // tp_basicsize, tp_itemsize
     // tp_doc
 
-    if (!cls->tp_new && base != object_cls)
-        cls->tp_new = base->tp_new;
-
     try {
         add_operators(cls);
     } catch (ExcInfo e) {

src/runtime/dict.cpp

@@ -550,6 +550,27 @@ extern "C" void dictViewGCHandler(GCVisitor* v, Box* b) {
     v->visit(view->d);
 }
 
+static int dict_init(PyObject* self, PyObject* args, PyObject* kwds) noexcept {
+    assert(isSubclass(self->cls, dict_cls));
+    try {
+        dictInit(static_cast<BoxedDict*>(self), static_cast<BoxedTuple*>(args), static_cast<BoxedDict*>(kwds));
+    } catch (ExcInfo e) {
+        setCAPIException(e);
+        return -1;
+    }
+    return 0;
+}
+
+static Box* dict_repr(PyObject* self) noexcept {
+    assert(isSubclass(self->cls, dict_cls));
+    try {
+        return dictRepr(static_cast<BoxedDict*>(self));
+    } catch (ExcInfo e) {
+        setCAPIException(e);
+        return NULL;
+    }
+}
+
 void setupDict() {
     dict_iterator_cls = new BoxedHeapClass(object_cls, &dictIteratorGCHandler, 0, sizeof(BoxedDict), false,
                                            "dictionary-itemiterator");
@@ -617,6 +638,20 @@ void setupDict() {
 
     dict_iterator_cls->freeze();
 
+    // Manually set some tp_* slots *after* calling freeze() -> fixup_slot_dispatchers().
+    // fixup_slot_dispatchers will insert a wrapper like slot_tp_init into tp_init, which calls the python-level
+    // __init__ function.  This is all well and good, until a C extension tries to subclass from dict and then
+    // creates a new tp_init function which calls Py_DictType.tp_init().  That tp_init is slot_tp_init, which calls
+    // self.__init__, which is the *subclasses* init function not dict's.
+    //
+    // This seems to happen pretty rarely, and only with dict, so for now let's just work around it by manually
+    // setting the couple functions that get used.
+    //
+    // I'm not sure if CPython has a better mechanism for this, since I assume they allow having extension classes
+    // subclass Python classes.
+    dict_cls->tp_init = dict_init;
+    dict_cls->tp_repr = dict_repr;
+
     dict_keys_cls->giveAttr(
         "__iter__", new BoxedFunction(boxRTFunction((void*)dictViewKeysIter, typeFromClass(dict_iterator_cls), 1)));
     dict_keys_cls->freeze();

test/tests/_collections_test.py

@@ -14,3 +14,6 @@ for i in d:
 
 while d:
     print d.popleft()
+
+d = _collections.defaultdict()
+print str(d), repr(d)