QTabBar lays out the tabs when the bar's size or content changes,
often lazily. This should not change the scroll offset of the tabbar,
which is controlled by the user, or at most when a tab needs to be made
visible (e.g. when it becomes the current tab).
Move the logic of updating the scoll offset into the makeVisible
function, so that the scroll is only adjusted to either leave no gap
between the last tab and the right edge of the widget of there is still
a scroll; or to reset it to 0 if there is enough space for the entire
tab bar. Since layoutTabs does show and hide the scroll buttons, we
cannot skip this when the buttons are invisible. However, the
normalizedScrollRect helper now needs to return the entire widget rect
if there are no visible scroll buttons.
Add a test case that simulates the previously broken behavior where
the scroll got unnecessarily reset to 0 when resizing.
Fixes: QTBUG-113140
Pick-to: 6.5
Change-Id: Ic19fbb82821ea09cc5e7646dcbce3aa7607909c2
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Santhosh Kumar <santhosh.kumar.selvaraj@qt.io>
Reviewed-by: Axel Spoerl <axel.spoerl@qt.io>
ca15f650a1