ScrollView: fix crash when scrolling with zero-sized item

Check if a Flickable type was actually set as the contentItem before
accessing the pointer. Also warn that using a type other than Flickable
is not supported.

Fixes: QTBUG-93039
Change-Id: I1470766c6de02b7b601edf1375791d3147f26ab5
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
(cherry picked from commit e7df2279bf5519703fd0b853abaa23947a599920)

3 files changed, 35 insertions, 1 deletions

diff --git a/src/quicktemplates2/qquickscrollbar.cpp b/src/quicktemplates2/qquickscrollbar.cpp
index fdbd4b31..1ac4b42d 100644
--- a/src/quicktemplates2/qquickscrollbar.cpp
+++ b/src/quicktemplates2/qquickscrollbar.cpp
@@ -869,6 +869,9 @@ class QQuickFriendlyFlickable : public QQuickFlickable
 
 void QQuickScrollBarAttachedPrivate::scrollHorizontal()
 {
+    if (!flickable)
+        return;
+
     QQuickFriendlyFlickable *f = reinterpret_cast<QQuickFriendlyFlickable *>(flickable);
 
     const qreal viewwidth = f->width();
@@ -881,6 +884,9 @@ void QQuickScrollBarAttachedPrivate::scrollHorizontal()
 
 void QQuickScrollBarAttachedPrivate::scrollVertical()
 {
+    if (!flickable)
+        return;
+
     QQuickFriendlyFlickable *f = reinterpret_cast<QQuickFriendlyFlickable *>(flickable);
 
     const qreal viewheight = f->height();
diff --git a/src/quicktemplates2/qquickscrollview.cpp b/src/quicktemplates2/qquickscrollview.cpp
index 387c30a5..0c9d8f3e 100644
--- a/src/quicktemplates2/qquickscrollview.cpp
+++ b/src/quicktemplates2/qquickscrollview.cpp
@@ -38,6 +38,7 @@
 #include "qquickpane_p_p.h"
 #include "qquickscrollbar_p_p.h"
 
+#include <QtQml/qqmlinfo.h>
 #include <QtQuick/private/qquickflickable_p.h>
 
 QT_BEGIN_NAMESPACE
@@ -575,7 +576,10 @@ void QQuickScrollView::contentItemChange(QQuickItem *newItem, QQuickItem *oldIte
         // assume/require that it has an explicit content size assigned.
         d->flickableHasExplicitContentWidth = true;
         d->flickableHasExplicitContentHeight = true;
-        d->setFlickable(qobject_cast<QQuickFlickable *>(newItem), false);
+        auto newItemAsFlickable = qobject_cast<QQuickFlickable *>(newItem);
+        if (newItem && !newItemAsFlickable)
+            qmlWarning(this) << "ScrollView only supports Flickable types as its contentItem";
+        d->setFlickable(newItemAsFlickable, false);
     }
     QQuickPane::contentItemChange(newItem, oldItem);
 }
diff --git a/tests/auto/controls/data/tst_scrollview.qml b/tests/auto/controls/data/tst_scrollview.qml
index 87c39509..453f7753 100644
--- a/tests/auto/controls/data/tst_scrollview.qml
+++ b/tests/auto/controls/data/tst_scrollview.qml
@@ -502,4 +502,28 @@ TestCase {
         compare(control.contentWidth, flickable.contentWidth)
         compare(control.contentHeight, flickable.contentHeight)
     }
+
+    Component {
+        id: zeroSizedContentItemComponent
+        ScrollView {
+            width: 100
+            height: 100
+            contentItem: Item {}
+        }
+    }
+
+    function test_zeroSizedContentItem() {
+        ignoreWarning(/ScrollView only supports Flickable types as its contentItem/)
+        let control = createTemporaryObject(zeroSizedContentItemComponent, testCase)
+        verify(control)
+
+        let verticalScrollBar = control.ScrollBar.vertical
+        verify(verticalScrollBar)
+        // Scrolling a ScrollView with a zero-sized contentItem shouldn't crash.
+        mouseDrag(verticalScrollBar, verticalScrollBar.width / 2, verticalScrollBar.height / 2, 0, 50)
+
+        let horizontalScrollBar = control.ScrollBar.horizontal
+        verify(verticalScrollBar)
+        mouseDrag(horizontalScrollBar, horizontalScrollBar.width / 2, horizontalScrollBar.height / 2, 50, 0)
+    }
 }