So trying to make some widget wrapper I just discovered that I need a make operator, which is bolted down as internal. Is there any way I can extend Widget to wrap Widgets around it?

When you create a new widget you need to subclass from Pane or Canvas.

Take a look at http://fantom.org/doc/fwt/pod-doc.html#customWidgets

Ok, new question, is there an elegant way to pass an extra information during Widget addition to a Pane? I tried to alter Widget.add(newWidget) to MyWidget.add(newWidget, "constraints") but it didn't work, sadly.

You cannot modify add since that is used for serialization. The workaround proposed (see #961) is to add a new Widget.layout field:

MyPane { MyWidget { layout="foo" }, }

Yeah, I've read that. Still, since there are no tickets what other ways could I achieve this?

Unfortunately there is no good way, thats why this is needed. The one case I used it, I think I used a map in my custom Pane and painfully assigned somewhere along these lines:

class MyPane { Widget:Str constraints := [:] }

MyPane
{
  b := Button("Foo")
  add(b)
  constraints[b] = "foo"
}

Thanks. In case you do implement it, will you make layout Obj or Str?