ListView highlight broken inside TabBar with initial size 0

The description is a bit convoluted but I hope the reproducers I am attaching should make it easier to understand.

When using a ListView as controlItem of a TabBar template that initially has size 0, the automatic highlight management of the ListView bugs out and doesn't render the highlight. According to gammaray the highlight is where it is meant to be and visible but it is not actually there visually.

I am attaching two different reproducers that I think point at the same root cause.

• TabBar1.qml has a TabBar with only implicit sizes. The blue highlight does not appear. When giving the TabBar explicit non-zero size it starts to work.
• TabBar2.qml is the same but with explicit height that initially is 0. This too fails to show the highlight.

I suspect in both cases the initial size is 0 and that is what triggers the bug.

This is working on Qt 6.6.3 but has regressed by Qt 6.7.3.

Downstream bug report: https://bugs.kde.org/show_bug.cgi?id=495948