QAbstractSlider: fix missing "emission" of SliderOrientationChange

QAbstractSlider::sliderChange() is not a signal, but a protected
function, carrying an enum (also protected) to inform subclasses about
changes in the base class.

A user reported (QTBUG-135597) that in 5.15 the function was not
called for SliderOrientationChange. A prior test addition confirmed
that this bug is in all active branches.

Add the missing call in setOrientation().

This _should_ replace the update() call, because the default
sliderChange() implementation already calls it (and setPageStep(),
e.g., relies on this behavior), but since SliderOrientationChange was
not emitted since Qt 5.0, I minimize regression risks and keep the
update() call, just in case a user wrote code where they forgot to
call Base::sliderChange() for SliderOrientationChange (and this never
showed because we never "emitted" that, up to now). The duplicate
update() calls will be merged by Qt's event loop, so are harmless.

A dev-only follow-up change will remove the update().

[ChangeLog][QtWidgets][QAbstractSlider] Fixed the missing "emission"
of protected sliderChange(SliderOrientationChange).

Amends the start of the public history.

Pick-to: 6.5 5.15
Fixes: QTBUG-135597
Change-Id: I4545d47d315a98a9a51134901a00fa369f720754
Reviewed-by: Axel Spoerl <[email protected]>
(cherry picked from commit c35f6851bfe8ba71c26d3896498c1510fcd4e42b)
Reviewed-by: Qt Cherry-pick Bot <[email protected]>
(cherry picked from commit 4b20e23ed7a7c32b6557e526bf88804c48ac8325)

2 files changed, 1 insertions, 4 deletions

diff --git a/src/widgets/widgets/qabstractslider.cpp b/src/widgets/widgets/qabstractslider.cpp
index 4e65fbac886..d2569c9934d 100644
--- a/src/widgets/widgets/qabstractslider.cpp
+++ b/src/widgets/widgets/qabstractslider.cpp
@@ -272,6 +272,7 @@ void QAbstractSlider::setOrientation(Qt::Orientation orientation)
         setSizePolicy(sizePolicy().transposed());
         setAttribute(Qt::WA_WState_OwnSizePolicy, false);
     }
+    sliderChange(SliderOrientationChange);
     update();
     updateGeometry();
 }
diff --git a/tests/auto/widgets/widgets/qabstractslider/tst_qabstractslider.cpp b/tests/auto/widgets/widgets/qabstractslider/tst_qabstractslider.cpp
index 04b1114c3d7..d0ab97b0afe 100644
--- a/tests/auto/widgets/widgets/qabstractslider/tst_qabstractslider.cpp
+++ b/tests/auto/widgets/widgets/qabstractslider/tst_qabstractslider.cpp
@@ -2139,12 +2139,8 @@ void tst_QAbstractSlider::sliderChange_impl()
 
     sl.setOrientation(sl.orientation() == Qt::Horizontal ? Qt::Vertical
                       /* else */                         : Qt::Horizontal);
-    QEXPECT_FAIL("", "QTBUG-135597", Continue);
     QCOMPARE(sl.changes.size(), 1U);
-    if (!sl.changes.empty()) {
-    QEXPECT_FAIL("", "QTBUG-135597", Continue);
     QCOMPARE(sl.changes.back(), SliderChange::SliderOrientationChange);
-    }
     sl.changes.clear();
 
     sl.setPageStep(1025); // unlikely to be the default ;)