QMdiArea: Fix top level window title when using DontMaximizeSubWindowOnActivation

When trying to find the original window title, check for another
maximized sub window and use its title. Protect the calls to
setWindowTitle to prevent the original title from being cleared.

Fixes: QTBUG-92240
Change-Id: I55175382ab261b4cf8b5528304adaaec4fbe2c31
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@qt.io>
(cherry picked from commit 8886462872db9cdab4d7683823fd24fb9f8920c4)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

2 files changed, 28 insertions, 4 deletions

diff --git a/src/widgets/widgets/qmdisubwindow.cpp b/src/widgets/widgets/qmdisubwindow.cpp
index 89d77574f0..1c03b02ab8 100644
--- a/src/widgets/widgets/qmdisubwindow.cpp
+++ b/src/widgets/widgets/qmdisubwindow.cpp
@@ -263,11 +263,28 @@ static inline ControlElement<T> *ptr(QWidget *widget)
     return nullptr;
 }
 
+QString QMdiSubWindowPrivate::originalWindowTitleHelper() const
+{
+    Q_Q(const QMdiSubWindow);
+    // QTBUG-92240: When DontMaximizeSubWindowOnActivation is set and
+    // there is another subwindow maximized, use its original title.
+    if (auto *mdiArea = q->mdiArea()) {
+        const auto &subWindows = mdiArea->subWindowList();
+        for (auto *subWindow : subWindows) {
+            if (subWindow != q && subWindow->isMaximized()) {
+                auto *subWindowD = static_cast<QMdiSubWindowPrivate *>(qt_widget_private(subWindow));
+                if (!subWindowD->originalTitle.isNull())
+                    return subWindowD->originalTitle;
+            }
+        }
+    }
+    return q->window()->windowTitle();
+}
+
 QString QMdiSubWindowPrivate::originalWindowTitle()
 {
-    Q_Q(QMdiSubWindow);
     if (originalTitle.isNull()) {
-        originalTitle = q->window()->windowTitle();
+        originalTitle = originalWindowTitleHelper();
         if (originalTitle.isNull())
             originalTitle = QLatin1String("");
     }
@@ -282,11 +299,17 @@ void QMdiSubWindowPrivate::setNewWindowTitle()
         return;
     QString original = originalWindowTitle();
     if (!original.isEmpty()) {
-        if (!original.contains(QMdiSubWindow::tr("- [%1]").arg(childTitle)))
-            q->window()->setWindowTitle(QMdiSubWindow::tr("%1 - [%2]").arg(original, childTitle));
+        if (!original.contains(QMdiSubWindow::tr("- [%1]").arg(childTitle))) {
+            auto title = QMdiSubWindow::tr("%1 - [%2]").arg(original, childTitle);
+            ignoreWindowTitleChange = true;
+            q->window()->setWindowTitle(title);
+            ignoreWindowTitleChange = false;
+        }
 
     } else {
+        ignoreWindowTitleChange = true;
         q->window()->setWindowTitle(childTitle);
+        ignoreWindowTitleChange = false;
     }
 }
 
diff --git a/src/widgets/widgets/qmdisubwindow_p.h b/src/widgets/widgets/qmdisubwindow_p.h
index d3513b6708..043cf92201 100644
--- a/src/widgets/widgets/qmdisubwindow_p.h
+++ b/src/widgets/widgets/qmdisubwindow_p.h
@@ -286,6 +286,7 @@ public:
 #endif
     void updateInternalWindowTitle();
     QString originalWindowTitle();
+    QString originalWindowTitleHelper() const;
     void setNewWindowTitle();
 
     inline int titleBarHeight() const