QHeaderView: fix spurious sorting

QHeaderView sorting may be triggered when the user performs
some mouse interactions that should really not result in sorting.

Generally speaking, this happens when the user:

* presses on a non-movable section (A)
* moves on another section (B)
* releases on that section

resulting in B becoming sorted / flipping sorting.

(Non-movable is required, otherwise dragging would cause section moving,
not sorting.)

To make the matter worse, QHeaderView doesn't check that the release
happens within its geometry. This makes sense when moving sections: one
is able to drag a section horizontally/vertically even if the mouse
leaves the QHeaderView.

But when not moving sections, this means that one can

* press on section (A),
* move the mouse anywhere vertically (for a horizontal bar, mut.mut
  for a vertical) above or below another section (B), that is,
  outside QHeaderView's geometry
* release the mouse

and cause B to be sorted.

Fix it by

1) remembering which one was the section that the user originally
clicked on; that's the only one that can possibly become sorted
(if we're not moving and other conditions hold). No other variable
seemed to remember this.

2) on release, check that it happens within that section's geometry.
If so, sort.

Change-Id: Icfb67662221efbde019711f933781ee1e7d9ac43
Reviewed-by: Christian Ehrlicher <ch.ehrlicher@gmx.de>
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@qt.io>
(cherry picked from commit b5b2640a65de20d05890fa9e6462bb7b88f83964)

3 files changed, 161 insertions, 6 deletions

diff --git a/src/widgets/itemviews/qheaderview.cpp b/src/widgets/itemviews/qheaderview.cpp
index 84e2fd72a9..3b396c689b 100644
--- a/src/widgets/itemviews/qheaderview.cpp
+++ b/src/widgets/itemviews/qheaderview.cpp
@@ -2528,7 +2528,7 @@ void QHeaderView::mousePressEvent(QMouseEvent *e)
     int handle = d->sectionHandleAt(pos);
     d->originalSize = -1; // clear the stored original size
     if (handle == -1) {
-        d->pressed = logicalIndexAt(pos);
+        d->firstPressed = d->pressed = logicalIndexAt(pos);
         if (d->clickableSections)
             emit sectionPressed(d->pressed);
 
@@ -2576,7 +2576,7 @@ void QHeaderView::mouseMoveEvent(QMouseEvent *e)
         // just before the mouseReleaseEvent and resets the state. This prevents
         // column dragging from working. So this code is disabled under Cocoa.
         d->state = QHeaderViewPrivate::NoState;
-        d->pressed = -1;
+        d->firstPressed = d->pressed = -1;
     }
     switch (d->state) {
         case QHeaderViewPrivate::ResizeSection: {
@@ -2705,9 +2705,27 @@ void QHeaderView::mouseReleaseEvent(QMouseEvent *e)
     case QHeaderViewPrivate::NoState:
         if (d->clickableSections) {
             int section = logicalIndexAt(pos);
-            if (section != -1 && section == d->pressed) {
-                d->flipSortIndicator(section);
-                emit sectionClicked(section);
+            if (section != -1 && section == d->firstPressed) {
+                QRect firstPressedSectionRect;
+                switch (d->orientation) {
+                case Qt::Horizontal:
+                    firstPressedSectionRect.setRect(sectionViewportPosition(d->firstPressed),
+                                                    0,
+                                                    sectionSize(d->firstPressed),
+                                                    d->viewport->height());
+                    break;
+                case Qt::Vertical:
+                    firstPressedSectionRect.setRect(0,
+                                                    sectionViewportPosition(d->firstPressed),
+                                                    d->viewport->width(),
+                                                    sectionSize(d->firstPressed));
+                    break;
+                };
+
+                if (firstPressedSectionRect.contains(e->pos())) {
+                    d->flipSortIndicator(section);
+                    emit sectionClicked(section);
+                }
             }
             if (d->pressed != -1)
                 updateSection(d->pressed);
@@ -2721,7 +2739,7 @@ void QHeaderView::mouseReleaseEvent(QMouseEvent *e)
         break;
     }
     d->state = QHeaderViewPrivate::NoState;
-    d->pressed = -1;
+    d->firstPressed = d->pressed = -1;
 }
 
 /*!
diff --git a/src/widgets/itemviews/qheaderview_p.h b/src/widgets/itemviews/qheaderview_p.h
index 766adef36d..0f6641c3df 100644
--- a/src/widgets/itemviews/qheaderview_p.h
+++ b/src/widgets/itemviews/qheaderview_p.h
@@ -82,6 +82,7 @@ public:
           originalSize(-1),
           section(-1),
           target(-1),
+          firstPressed(-1),
           pressed(-1),
           hover(-1),
           length(0),
@@ -274,6 +275,7 @@ public:
     int originalSize;
     int section; // used for resizing and moving sections
     int target;
+    int firstPressed;
     int pressed;
     int hover;
 
diff --git a/tests/auto/widgets/itemviews/qheaderview/tst_qheaderview.cpp b/tests/auto/widgets/itemviews/qheaderview/tst_qheaderview.cpp
index d5813d64ff..c355ee9665 100644
--- a/tests/auto/widgets/itemviews/qheaderview/tst_qheaderview.cpp
+++ b/tests/auto/widgets/itemviews/qheaderview/tst_qheaderview.cpp
@@ -218,6 +218,7 @@ private slots:
     void QTBUG75615_sizeHintWithStylesheet();
     void ensureNoIndexAtLength();
     void offsetConsistent();
+    void sectionsDontSortWhenNotClickingInThem();
 
     void initialSortOrderRole();
 
@@ -2628,6 +2629,140 @@ void tst_QHeaderView::offsetConsistent()
     QVERIFY(offset2 > offset1);
 }
 
+void tst_QHeaderView::sectionsDontSortWhenNotClickingInThem()
+{
+    QTableView qtv;
+    QStandardItemModel amodel(1000, 4);
+    qtv.setModel(&amodel);
+    QHeaderView *hv = qtv.horizontalHeader();
+    hv->setSectionsClickable(true);
+    hv->setFirstSectionMovable(true);
+    hv->setSectionsMovable(false);
+
+    enum { DefaultYOffset = 5, OutOfRangeYOffset = 10000 };
+
+    const auto pressOnSection = [&](int section, int yOffset = DefaultYOffset)
+    {
+        QTest::mousePress(hv->viewport(), Qt::LeftButton, Qt::NoModifier,
+                          QPoint(hv->sectionViewportPosition(section) + hv->sectionSize(section) / 2, yOffset));
+    };
+    const auto moveOntoSection = [&](int section, int yOffset = DefaultYOffset)
+    {
+        QTest::mouseMove(hv->viewport(),
+                         QPoint(hv->sectionViewportPosition(section) + hv->sectionSize(section) / 2, yOffset));
+    };
+    const auto releaseOnSection = [&](int section, int yOffset = DefaultYOffset)
+    {
+        QTest::mouseRelease(hv->viewport(), Qt::LeftButton, Qt::NoModifier,
+                            QPoint(hv->sectionViewportPosition(section) + hv->sectionSize(section) / 2, yOffset));
+    };
+
+    hv->setSortIndicator(-1, Qt::AscendingOrder);
+    QCOMPARE(hv->sortIndicatorSection(), -1);
+
+    pressOnSection(0);
+    releaseOnSection(0);
+    // RESULT: sorting
+    QCOMPARE(hv->sortIndicatorSection(), 0);
+
+    hv->setSortIndicator(-1, Qt::AscendingOrder);
+    QCOMPARE(hv->sortIndicatorSection(), -1);
+
+    pressOnSection(0);
+    moveOntoSection(1);
+    releaseOnSection(1);
+    // RESULT: no sorting
+    QCOMPARE(hv->sortIndicatorSection(), -1);
+
+    pressOnSection(0);
+    moveOntoSection(1);
+    moveOntoSection(2);
+    releaseOnSection(2);
+    // RESULT: no sorting
+    QCOMPARE(hv->sortIndicatorSection(), -1);
+
+    pressOnSection(0);
+    moveOntoSection(1);
+    moveOntoSection(0);
+    releaseOnSection(0);
+    // RESULT: sorting by 0
+    QCOMPARE(hv->sortIndicatorSection(), 0);
+
+    pressOnSection(0);
+    moveOntoSection(1);
+    releaseOnSection(1);
+    // RESULT: no change, still sorting by 0
+    QCOMPARE(hv->sortIndicatorSection(), 0);
+
+    auto sortOrder = hv->sortIndicatorOrder();
+    pressOnSection(1);
+    moveOntoSection(0);
+    releaseOnSection(0);
+    // RESULT: no change, still sorting by 0
+    QCOMPARE(hv->sortIndicatorSection(), 0);
+    QCOMPARE(hv->sortIndicatorOrder(), sortOrder);
+
+    pressOnSection(1);
+    moveOntoSection(0);
+    moveOntoSection(1);
+    releaseOnSection(1);
+    // RESULT: sorting by 1
+    QCOMPARE(hv->sortIndicatorSection(), 1);
+
+    pressOnSection(1);
+    moveOntoSection(0);
+    releaseOnSection(0);
+    // RESULT: no change, still sorting by 1
+    QCOMPARE(hv->sortIndicatorSection(), 1);
+
+    hv->setSortIndicator(-1, Qt::AscendingOrder);
+    QCOMPARE(hv->sortIndicatorSection(), -1);
+
+    pressOnSection(0);
+    releaseOnSection(0, OutOfRangeYOffset);
+    // RESULT: no sorting
+    QCOMPARE(hv->sortIndicatorSection(), -1);
+
+    pressOnSection(0);
+    moveOntoSection(0, OutOfRangeYOffset);
+    releaseOnSection(0, OutOfRangeYOffset);
+    // RESULT: no sorting
+    QCOMPARE(hv->sortIndicatorSection(), -1);
+
+    pressOnSection(0);
+    moveOntoSection(0, OutOfRangeYOffset);
+    moveOntoSection(0);
+    releaseOnSection(0);
+    // RESULT: sorting by 0
+    QCOMPARE(hv->sortIndicatorSection(), 0);
+
+    pressOnSection(1);
+    releaseOnSection(1, OutOfRangeYOffset);
+    // RESULT: no change, still sorting by 0
+    QCOMPARE(hv->sortIndicatorSection(), 0);
+
+    pressOnSection(1);
+    moveOntoSection(1, OutOfRangeYOffset);
+    releaseOnSection(1, OutOfRangeYOffset);
+    // RESULT: no change, still sorting by 0
+    QCOMPARE(hv->sortIndicatorSection(), 0);
+
+    pressOnSection(1);
+    moveOntoSection(1, OutOfRangeYOffset);
+    moveOntoSection(1);
+    releaseOnSection(1);
+    // RESULT: sorting by 1
+    QCOMPARE(hv->sortIndicatorSection(), 1);
+
+    pressOnSection(2);
+    moveOntoSection(1);
+    moveOntoSection(2);
+    moveOntoSection(2, OutOfRangeYOffset);
+    releaseOnSection(2, OutOfRangeYOffset);
+    // RESULT: no change, still sorting by 1
+    QCOMPARE(hv->sortIndicatorSection(), 1);
+}
+
 void tst_QHeaderView::initialSortOrderRole()
 {
     QTableView view; // ### Shadowing member view (of type QHeaderView)