fix: use original dict (#5658)

* fix: use original dict

Signed-off-by: Henry Schreiner <[email protected]>

* refactor: handle unset dict just in case

Signed-off-by: Henry Schreiner <[email protected]>

---------

Signed-off-by: Henry Schreiner <[email protected]>

Author: henryiii

include/pybind11/detail/init.h

@@ -451,7 +451,16 @@ void setstate(value_and_holder &v_h, std::pair<T, O> &&result, bool need_alias)
         // See PR #2972 for details.
         return;
     }
-    setattr((PyObject *) v_h.inst, "__dict__", d);
+    // Our tests never run into an unset dict, but being careful here for now (see #5658)
+    auto dict = getattr((PyObject *) v_h.inst, "__dict__", none());
+    if (dict.is_none()) {
+        setattr((PyObject *) v_h.inst, "__dict__", d);
+    } else {
+        // Keep the original object dict and just update it
+        if (PyDict_Update(dict.ptr(), d.ptr()) < 0) {
+            throw error_already_set();
+        }
+    }
 }
 
 /// Implementation for py::pickle(GetState, SetState)

tests/test_pickling.cpp

@@ -35,10 +35,7 @@ void wrap(py::module m) {
         .def_readwrite("num", &SimpleBase::num)
         .def(py::pickle(
             [](const py::object &self) {
-                py::dict d;
-                if (py::hasattr(self, "__dict__")) {
-                    d = self.attr("__dict__");
-                }
+                py::dict d = py::getattr(self, "__dict__", py::dict());
                 return py::make_tuple(self.attr("num"), d);
             },
             [](const py::tuple &t) {