classderived: handle tp_dealloc called after tp_clear

lostmsu · lostmsu · commit 38b3f01ad70f · 2020-12-17T22:46:40.000-08:00
Because tp_clear sets tpHandle to NULL, it can't be used.
Fortunately, we can simply read object's type from pyHandle.
diff --git a/src/runtime/classderived.cs b/src/runtime/classderived.cs
@@ -75,7 +75,8 @@ internal ClassDerivedObject(Type tp) : base(tp)
             // So we don't call PyObject_GC_Del here and instead we set the python
             // reference to a weak reference so that the C# object can be collected.
             GCHandle gc = GCHandle.Alloc(self, GCHandleType.Weak);
-            Marshal.WriteIntPtr(self.pyHandle, ObjectOffset.magic(self.tpHandle), (IntPtr)gc);
+            int gcOffset = ObjectOffset.magic(Runtime.PyObject_TYPE(self.pyHandle));
+            Marshal.WriteIntPtr(self.pyHandle, gcOffset, (IntPtr)gc);
             self.gcHandle.Free();
             self.gcHandle = gc;
         }
