QMdiArea: fix initial single-sub-window in TabbedView

This is somewhat of a corner case, where there is a single sub-window,
setViewMode(TabbedView) is called before addSubWindow(), and the latter
is called before show(). The sub-window would be active, i.e.
subwindow->d_func()->isActive is true and QMdiArea::aboutToActivate() is
emitted, but QMA::emitSubWindowActivated() is never called for that
sub-window, resulting in that sub-window shown as
unmaximized/with-a-title-bar instead of as maximized/tabbed as is
expected in TabbedView.

Pick-to: 6.6 6.5
Fixes: QTBUG-114188
Change-Id: Ia7b2cfd07c51867707866a1f99f70129bbdc0e3e
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@qt.io>

1 files changed, 16 insertions, 0 deletions

diff --git a/tests/auto/widgets/widgets/qmdiarea/tst_qmdiarea.cpp b/tests/auto/widgets/widgets/qmdiarea/tst_qmdiarea.cpp
index 1aa99f27cf..af604372ea 100644
--- a/tests/auto/widgets/widgets/qmdiarea/tst_qmdiarea.cpp
+++ b/tests/auto/widgets/widgets/qmdiarea/tst_qmdiarea.cpp
@@ -260,6 +260,7 @@ private slots:
     void task_236750();
     void qtbug92240_title_data();
     void qtbug92240_title();
+    void tabbedview_singleSubWindow();
     void tabbedview_activefirst();
     void tabbedview_activesecond();
     void tabbedview_activethird();
@@ -2728,6 +2729,21 @@ void tst_QMdiArea::qtbug92240_title()
     QTRY_COMPARE(w.windowTitle(), QLatin1String("QTBUG-92240 - [2]"));
 }
 
+void tst_QMdiArea::tabbedview_singleSubWindow()
+{
+    // With only one sub-window, setViewMode() before addSubWindow(); and addSubWindow()
+    // before show(), ensure the sub-window is properly activated.
+    QMdiArea mdiArea;
+    mdiArea.setViewMode(QMdiArea::TabbedView);
+    auto *w = new QWidget(&mdiArea);
+    mdiArea.addSubWindow(w);
+    mdiArea.show();
+    QVERIFY(QTest::qWaitForWindowExposed(&mdiArea));
+    auto *sub = mdiArea.subWindowList().at(0);
+    QCOMPARE(mdiArea.activeSubWindow(), sub);
+    QVERIFY(sub->isMaximized());
+}
+
 static void setupMdiAreaWithTabbedView(QMdiArea &mdiArea)
 {
     mdiArea.setViewMode(QMdiArea::TabbedView);