The space reserved for the text of a QDockWidget tab is not enough in some situations

Hi all,

I was pretty sure this was a KDE issue, so I filed Bug #489516: https://bugs.kde.org/show_bug.cgi?id=489516 . There, I was told they're sure it's an upstream bug, and I should report it here. So here we go:

Using a Plasma 6 desktop and Noto Sans 10pt as the font, it happens that when tabifying QDockWidgets of a Qt 6 program, the resulting tab texts are sometimes cut off, although there would be enough space. Please see the attached screenshots. This happens both with Breeze and Fusion, so I think it's no style issue.

I can produce this exact behavior on my Gentoo desktop and also on my Artix notebook. Both running plasma 6.1.1, Gentoo with Qt 6.7.1, Artix with 6.7.2.

This does not happen when using a Plasma 5 desktop, neither for a Qt 5 build, nor for a Qt 6 build. Everything is fine using Plasma 5. I tried this using a current KUbuntu in a QEMU VM. Both the Qt 5 and 6 builds of my demo don't cut off the text.

But I could also reproduce this using am OpenSUSE Tumbleweed QEMU VM, running a Plasma 6 desktop. Here, the Qt 5 build looks fine, but the Qt 6 build cuts off the text, just as with my Gentoo and Artix machines.

Interestingly, the cutoff does not happen when:

• Another font is used
• Noto Sans is used, but another size (9 or 11)
• The docks are not hidden first
• The docks are hidden after a small delay, e.g. by a QTimer::singleShot waiting 100 ms (0 ms has the same result as hiding them directly)
• The name of the cut off dock is slightly changed, e.g. from "Ergebnisse" to "ErgebnisseX", "Ergebnisse " or similar
• The name of the "Extras" menu entry is changed, e.g. from "Extras" to "X" (how can that ever affect this at all?!)

Well, as said, this is an odd one ... I'd really love to help tracking this down if I can!