ListView: take section size into account while snapping an item into place

In case the sections are displayed using ViewSection.CurrentLabelAtStart,
the section size should be taken into account while snapping the items.
This patch extends the fixup() method to perform such checks.
The drawback of this approach is that the position adjustment takes
some time (because of the animation) and happens after the scrolling is
finished.
A better solution would be to fix the scrolling process in such a way,
that no adjustment is needed during fixup.

Fixes: QTBUG-30768
Pick-to: 6.2
Change-Id: I31a1a3af55afe8be4e8d7980cbb163622e3283bc
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>
(cherry picked from commit 249fe4b)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
(cherry picked from commit b29bfa7)
(cherry picked from commit 174e6b5)

Author: isolovev

src/quick/items/qquicklistview.cpp

@@ -1797,6 +1797,19 @@ void QQuickListViewPrivate::fixup(AxisData &data, qreal minExtent, qreal maxExte
             QQuickItemViewPrivate::fixup(data, minExtent, maxExtent);
             return;
         }
+        // If we have the CurrentLabelAtStart flag set, then we need to consider
+        // the section size while calculating the position
+        if (sectionCriteria
+            && (sectionCriteria->labelPositioning() & QQuickViewSection::CurrentLabelAtStart)
+            && currentSectionItem) {
+            auto sectionSize = (orient == QQuickListView::Vertical) ? currentSectionItem->height()
+                                                                    : currentSectionItem->width();
+            if (isContentFlowReversed())
+                pos += sectionSize;
+            else
+                pos -= sectionSize;
+        }
+
         pos = qBound(-minExtent, pos, -maxExtent);
 
         qreal dist = qAbs(data.move + pos);

tests/auto/quick/qquicklistview/data/snapToItemWithSectionAtStart.qml

@@ -0,0 +1,52 @@
+import QtQuick
+
+ListView {
+    id: listView
+    width: 240
+    height: 300
+
+    model: ListModel {
+        ListElement { section: "section 1" }
+        ListElement { section: "section 1" }
+        ListElement { section: "section 1" }
+        ListElement { section: "section 2" }
+        ListElement { section: "section 2" }
+        ListElement { section: "section 2" }
+        ListElement { section: "section 3" }
+        ListElement { section: "section 3" }
+        ListElement { section: "section 3" }
+        ListElement { section: "section 4" }
+        ListElement { section: "section 4" }
+        ListElement { section: "section 4" }
+        ListElement { section: "section 5" }
+        ListElement { section: "section 5" }
+        ListElement { section: "section 5" }
+    }
+
+    section.property: "section"
+    section.labelPositioning: ViewSection.InlineLabels | ViewSection.CurrentLabelAtStart
+    section.delegate: Rectangle {
+        width: listView.width
+        height: 30
+        Text {
+            anchors.fill: parent
+            text: section
+        }
+        color: "lightblue"
+    }
+
+    snapMode: ListView.SnapToItem
+
+    delegate: Rectangle {
+        width: listView.width
+        height: 30
+        Text {
+            anchors.fill: parent
+            text: index
+        }
+        border {
+            width: 1
+            color: "black"
+        }
+    }
+}

tests/auto/quick/qquicklistview/tst_qquicklistview.cpp

@@ -171,6 +171,7 @@ private slots:
     void headerSnapToItem_data();
     void headerSnapToItem();
     void snapToItemWithSpacing_QTBUG_59852();
+    void snapToItemWithSectionAtStart();
     void snapOneItemResize_QTBUG_43555();
     void snapOneItem_data();
     void snapOneItem();
@@ -5395,6 +5396,27 @@ void tst_QQuickListView::snapToItemWithSpacing_QTBUG_59852()
     releaseView(window);
 }
 
+void tst_QQuickListView::snapToItemWithSectionAtStart() // QTBUG-30768
+{
+    QQuickView window;
+    QVERIFY(QQuickTest::showView(window, testFileUrl("snapToItemWithSectionAtStart.qml")));
+    QQuickListView *listView = qobject_cast<QQuickListView *>(window.rootObject());
+    QTRY_VERIFY(listView);
+
+    // Both sections and elements are 30px high. The list height is 300px, so
+    // it fits exactly 10 elements. We can do some random flicks, but the
+    // content position always MUST be divisible by 30.
+    for (int i = 0; i < 10; ++i) {
+        const bool even = (i % 2 == 0);
+        const QPoint start = even ? QPoint(20, 100 + i * 5) : QPoint(20, 20 + i * 3);
+        const QPoint end = even ? start - QPoint(0, 50 + i * 10) : start + QPoint(0, 50 + i * 5);
+
+        flick(&window, start, end, 180);
+        QTRY_COMPARE(listView->isMoving(), false); // wait until it stops
+        QCOMPARE(int(listView->contentY()) % 30, 0);
+    }
+}
+
 static void drag_helper(QWindow *window, QPoint *startPos, const QPoint &delta)
 {
     QPoint pos = *startPos;