If an application-wide style sheet is set, a QSpinBox takes too much vertical space – no matter what the style sheet is (it's only important that one is set, no matter if QSpinBox is part of it or not). Doesn't happen if Fusion is used, so this seems to be caused by Breeze. I'll attach a minimal example along with some screen shots after filing this bug. I didn't see this everywhere, so I played around a bit. I can't reproduce this on my Gentoo desktop, but I see it on my Artix notebook. Also tested with fresh users. I also see it in a freshly installed bare KDE OpenSuse Tumbleweed VM. I don't see it on an Artix machine in my office though. I thus investigated the installed package versions. All machines run Plasma 6.2.5 and Frameworks 6.10.0 – but the machines where I see the bug have Qt 6.8.2 already, whereas the machines where I don't see it still have Qt 6.8.1. So I think this may be caused by some change between Qt 6.8.1 and 6.8.2. No matter what Qt version is installed, I don't see this when using the Fusion style. I'll try to upgrade either my Gentoo and/or my office Artix machine to see if this is actually only caused by Qt.
Created attachment 178210 [details] CMakeLists.txt
Created attachment 178211 [details] main.cpp
Created attachment 178213 [details] MainWindow.cpp
Created attachment 178214 [details] MainWindow.h
Created attachment 178215 [details] QLineEdit and QSpinBox have the same height using Fusion, no matter if a style sheet is set
Created attachment 178216 [details] QLineEdit and QSpinBox have the same height using Breeze if no style sheet is set
Created attachment 178217 [details] The QSpinBox is rendered too high if an application-wide syle sheet is set and Breeze is used
Additional info: I posted this also on the Qt forums (cf. https://forum.qt.io/topic/160958/ ), hoping to gather more information about this. Decently, Christian Ehrlicher relied at once and mentioned the following two changes that may have caused this: https://codereview.qt-project.org/c/qt/qtbase/+/601315 https://codereview.qt-project.org/c/qt/qtbase/+/613831 He said: "Maybe breeze had some kind of workaround for this which is now doing wrong calculations"
I just tested it again using my Qt 6.8.1 Artix machine. After updating to Qt 6.8.2, I see it there, too. Here we are.
I added some debug output and to me it looks like a bug in Qt StyleSheetStyle. Without a stylesheet content Breeze sizeFromContents returns QSize(52, 32). WIth a stylesheet it returns the same value. However stylesheet style goes into this clause https://invent.kde.org/qt/qt/qtbase/-/blob/6.8.2/src/widgets/styles/qstylesheetstyle.cpp?ref_type=heads#L5317 and returns QSize(64, 44) looking more closely rule.hasBorder() is true (rule.box() is null and rule.hasNativeBorder() is true). With fusion the base style returns QSize(42, 23) and stylesheet style expands that to QSize(48, 29). Not sure why there is no visible difference but I have no knowledge about the QStyleSheet implementation. I am sorry but I think we need to send this back to Qt.
Thanks a lot for the quick follow-up! Did you file an upstream bug report already? I would really like to be up to date about this, because this is a really annoying regression …
Nevermind, I just did, gathering all we know until now: https://bugreports.qt.io/browse/QTBUG-133845
No I didn't do it yet. I can do it tomorrow if you prefer me doing that.
Sorry I answered after reading your first comment in my email client then read the second one :D
You're welcome ;-) Feel free to comment on that report though!