Meaning of "Exported component .. doesn't inherit Window. This is deprecated"

[kermitfrog]

When I have something like this

export component C inherits ListView {}

then slint gives me a warning Exported component 'C' doesn't inherit Window. This is deprecated.

But I can not find anything on why this happens. Not even a hint in the docs that this could be a problem. So...

1. Why should every exported component inherit from Window?
2. Can not inheriting Window cause any problems in the current version?
3. How exactly am I supposed to implement this?
   a) is there some syntax for multiple inheritance?
   b) Or do I have to do something like this for every component I want exported:

component CBase inherits ListView {}
export component C inherits Window {
  CBase {}
}

[ogoffart]

Currently, all exported component from the main file gets generated as Windows for legacy reason. Meaning that the generated code will have show, hide function and all window specific stuff.

But in the future we want to be able to export component that are not Window for re-use inside other components and that's why we deprecated exporting component that are not explicitly Window now.

So yes, the code you are pasting is the right way to do it.

[kermitfrog]

Ok, that makes sense.

Trying to actually write the code like this introduces additional complexity. So I had to declare and forwarding a few properties -- more work, but no big thing.

But the result still does not behave exactly as before.

in my main.slint file I use the component in a HorizontalBox.
Before, this if would be like

HorizontalBox {
  C {}
  ...
}

With the same code in main.slint, and the component wrapped the width of C is 0;
I have tried the following (in Cs definition) without success:
preferred-width: 100%;
min-width: child.min-width;
preferred-width: child.preferred-width;

The only thing that works is:

HorizontalBox {
  C {
    width: 50%;
  }
  ...
}

What am I missing?

EDIT:
Ok, this worked:
horizontal-stretch: child.horizontal-stretch;

But that means, I need to forward pretty much all layouting/size properties for it to be sized correctly in every situation, right?
If we're supposed to wrap all components in something inheriting window... what is the full list of properties that need to be set?
For now, ignoring the warning seems to be the better choice.
END EDIT

---

Another thing that does not make sense to me:
CBase in this case inherits from another component, which in turn inherits from ListView.
I have another component that also inherits from ListView (and not Window), but exporting that one will not give me a warning.