[fpc-devel] Can someone confirm if this is a bug? (ancestor in TWRiter.WriteProperty)

[Martin]

Paul Ishenin wrote:
> Michael Van Canneyt wrote:
>>>
>>> when you get to write TPersistenChild  you enter the following code
>>>
>>>   tkClass:
>>>     begin
>>>       ObjValue := TObject(GetObjectProp(Instance, PropInfo));
>>>       if HasAncestor then
>>>       begin
>>>         AncestorObj := TObject(GetObjectProp(Ancestor, PropInfo));
>>>         if Assigned(AncestorObj) then
>>>           if Assigned(ObjValue) and
>>>             (TComponent(AncestorObj).Owner = FRootAncestor) and
>>>             (TComponent(ObjValue).Owner = Root) and
>>>             (UpperCase(TComponent(AncestorObj).Name) = 
>>> UpperCase(TComponent(ObjValue).Name)) then
>>>             AncestorObj := ObjValue
>>> //            else
>>> //              AncestorObj := nil;
>>>       end else
>>>         AncestorObj := nil;
>>> --------------
>>>
>>> TObject(GetObjectProp(Ancestor, PropInfo));  returns the 
>>> TpersistentChil
>>> as well as ObjValue being TPersistent
>>>
>>>
>>> both get casted to TComponent with no check?
>> I may have mis-judged t, but the problem is still the same:
>>
>> Ancestors can only be a TComponent.
> Ancestor (in this report http://bugs.freepascal.org/view.php?id=14364) 
> is TLabel, HasAncestor = True (since Ancestor is TLabel and 
> Instance.ClassType = Ancestor.ClassType) and both ObjValue and 
> AncestorObj are TAnchorSide (descendant of TPersistent and not 
> TComponent). Therefore it accessing TAnchorSide property (TPersistent) 
> as TComponent and we have a crash.
>
> But maybe the problem is somewhere else. For example can Ancestor be 
> TLabel or it is usually some form, frame or datamodule?

and on top of that, Ancestor can be a TPersitent:
because if the AnchorSide writes it's properties, the following code, 
sts ancestor to anchorside:

      begin
            SavedAncestor := Ancestor;
            SavedPropPath := FPropPath;
            try
              FPropPath := FPropPath + PPropInfo(PropInfo)^.Name + '.';
              if HasAncestor then
                Ancestor := TPersistent(GetObjectProp(Ancestor, 
PropInfo));  // <<<<<
              WriteProperties(TPersistent(ObjValue));
            finally
              Ancestor := SavedAncestor;
              FPropPath := SavedPropPath;
            end;