From c94bcecb22bce80101de79f4b3c0aff143ff34b5 Mon Sep 17 00:00:00 2001
From: Ahmad Samir <a.samirh78@gmail.com>
Date: Mon, 6 Nov 2023 22:42:19 +0200
Subject: [PATCH] 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>
---
 src/widgets/widgets/qmdiarea.cpp                 |  5 +++++
 src/widgets/widgets/qmdisubwindow.h              |  1 +
 .../widgets/widgets/qmdiarea/tst_qmdiarea.cpp    | 16 ++++++++++++++++
 3 files changed, 22 insertions(+)

diff --git a/src/widgets/widgets/qmdiarea.cpp b/src/widgets/widgets/qmdiarea.cpp
index 29788932053..79b83453aca 100644
--- a/src/widgets/widgets/qmdiarea.cpp
+++ b/src/widgets/widgets/qmdiarea.cpp
@@ -2376,6 +2376,11 @@ void QMdiArea::showEvent(QShowEvent *showEvent)
         for (QMdiSubWindow *window : copy) {
             if (!window)
                 continue;
+            if (d->viewMode == TabbedView && window->d_func()->isActive && !d->active) {
+                d->showActiveWindowMaximized = true;
+                d->emitWindowActivated(window); // Also maximizes the window
+                continue;
+            }
             if (!window->testAttribute(Qt::WA_Resized)) {
                 QSize newSize(window->sizeHint().boundedTo(viewport()->size()));
                 window->resize(newSize.expandedTo(qSmartMinSize(window)));
diff --git a/src/widgets/widgets/qmdisubwindow.h b/src/widgets/widgets/qmdisubwindow.h
index a34c0249ecb..4227f02dac7 100644
--- a/src/widgets/widgets/qmdisubwindow.h
+++ b/src/widgets/widgets/qmdisubwindow.h
@@ -101,6 +101,7 @@ private:
     Q_PRIVATE_SLOT(d_func(), void _q_enterInteractiveMode())
     Q_PRIVATE_SLOT(d_func(), void _q_processFocusChanged(QWidget *, QWidget *))
     friend class QMdiAreaPrivate;
+    friend class QMdiArea;
 #if QT_CONFIG(tabbar)
     friend class QMdiAreaTabBar;
 #endif
diff --git a/tests/auto/widgets/widgets/qmdiarea/tst_qmdiarea.cpp b/tests/auto/widgets/widgets/qmdiarea/tst_qmdiarea.cpp
index 1aa99f27cf8..af604372ea8 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);