On Fri, 21 May 2021, Martin Frb via fpc-devel wrote:
If you have a readonly property such as
(tested with 3.2.2 rc)
TMyComponent = class(TComponent)
private
FFoo: TComponent;
published
property ReadOnly: TComponent read FFoo;
end;
and FFoo is nil,
then TWriter will crash.
Is the above scenario forbidden to be implemented (and therefore the
crash a result of breaking some rule)
or should that work (and the crash is a bug)?
From 3.2.2 rc sources:
procedure TWriter.WriteProperty(Instance: TPersistent; PropInfo: Pointer);
begin
// do not stream properties without getter
if not Assigned(PPropInfo(PropInfo)^.GetProc) then
exit;
// properties without setter are only allowed, if they are subcomponents
PropType := PPropInfo(PropInfo)^.PropType;
if not Assigned(PPropInfo(PropInfo)^.SetProc) then begin
if PropType^.Kind<>tkClass then
exit;
ObjValue := TObject(GetObjectProp(Instance, PropInfo));
if not ObjValue.InheritsFrom(TComponent) or //
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
not (csSubComponent in TComponent(ObjValue).ComponentStyle) then
exit;
end;
The marked line calls InheritsFrom on a nil value.
Definitely a bug. It should not crash. Please file a bugreport...
Michael.
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