The panic is

thread 'main' panicked at /Users/simon/src/slint/internal/core/properties.rs:523:9:
Recursion detected

That means that there's a circular dependency. For example:

At least in case of the direct use (without wrapper), root.width refers to the Window's width. And that in turn doesn't depend directly on the constraints of the layout.

But shouldn't the wrapper with width: 100% just take the parents width and do not depend on the layout?

A workaround is to make the whole layout conditional:

component WrapperInherited inherits Rectangle {
    if root.width > 200px: VerticalLayout {
        if root.width > 200px: Rectangle { }
    }
}

I am not sure if this only works because of #407.

Or is there another way to achieve the behaviour I want? In a nested layout tree, I want to use a vertical layout on small screens, and a horizontal on larger ones.

Another workaround is to wrap the WrapperInherited inside a rectangle:

component WrapperInherited inherits Rectangle {
    VerticalLayout {
        if root.width > 200px: Rectangle { }
    }
}

export component Test inherits Window {

    VerticalLayout {
        HorizontalLayout {
            Rectangle {
                WrapperInherited { }
            }
        }
    }
}

I am not sure why it works, and also not if this is desired behaviour or if it will change. This does not work with the non-inherited Wrapper.

Recursion detected means that there is a binding loop, which was not detected by the compiler at compile time. I'm fixing the compiler in #7132 to properly detect the loop at compile time.

I think you're right that your workaround only work because of #407.
But I think we'll have anyway to be careful when fixing that bug.
Given the current issues with layout I think we'll probably going to rework that and have a new layouting system and somehow keep both systems for compatibility. (And opt-in the new system with a pragma or edition or something like that)

Thx for the insights. I think it is a great idea to keep both systems around.
That way I can focus on achieving the layouts I want now and do not need to worry about breaking changes 👍