Ensure that child windows are visible again when showing their parent

When a window is closed, then it will cause the child windows to be
closed as well as a result. Therefore in order to ensure that they are
shown again as a result, we need to remove the WA_WState_ExplicitShowHide
attribute if the widget was not already hidden before. This enables us to
test for this attribute when calling showChildren(), so that if the
window has a windowHandle then we can make sure that this widget is shown
again.

Fixes: QTBUG-73021
Change-Id: I1186242b889899dfcd38d782a67567348e2055ee
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>
(cherry picked from commit ccd3bf0871b81dfc09bb469b161f32dfb47ee53e)

src/widgets/kernel/qwidget.cpp

@@ -1,4 +1,4 @@
-/****************************************************************************
+/****************************************************************************
 **
 ** Copyright (C) 2017 The Qt Company Ltd.
 ** Copyright (C) 2016 Intel Corporation.
@@ -8445,6 +8445,8 @@ void QWidgetPrivate::showChildren(bool spontaneous)
     QList<QObject*> childList = children;
     for (int i = 0; i < childList.size(); ++i) {
         QWidget *widget = qobject_cast<QWidget*>(childList.at(i));
+        if (widget && widget->windowHandle() && !widget->testAttribute(Qt::WA_WState_ExplicitShowHide))
+            widget->setAttribute(Qt::WA_WState_Hidden, false);
         if (!widget
             || widget->isWindow()
             || widget->testAttribute(Qt::WA_WState_Hidden))

src/widgets/kernel/qwidgetwindow.cpp

@@ -72,10 +72,18 @@ public:
     void setVisible(bool visible) override
     {
         Q_Q(QWidgetWindow);
-        if (QWidget *widget = q->widget())
+        if (QWidget *widget = q->widget()) {
+            // Check if the widget was already hidden, as this indicates it was done
+            // explicitly and not because the parent window in this case made it hidden.
+            // In which case do not automatically show the widget when the parent
+            // window is shown.
+            const bool wasHidden = widget->testAttribute(Qt::WA_WState_Hidden);
             QWidgetPrivate::get(widget)->setVisible(visible);
-        else
+            if (!wasHidden)
+                widget->setAttribute(Qt::WA_WState_ExplicitShowHide, false);
+        } else {
             QWindowPrivate::setVisible(visible);
+        }
     }
 
     QWindow *eventReceiver() override {

tests/auto/widgets/kernel/qwidget/tst_qwidget.cpp

@@ -395,6 +395,7 @@ private slots:
     void tabletTracking();
 
     void closeEvent();
+    void closeWithChildWindow();
 
 private:
     bool ensureScreenSize(int width, int height);
@@ -11067,5 +11068,27 @@ void tst_QWidget::closeEvent()
     QCOMPARE(widget.closeCount, 1);
 }
 
+void tst_QWidget::closeWithChildWindow()
+{
+    QWidget widget;
+    auto childWidget = new QWidget(&widget);
+    childWidget->setAttribute(Qt::WA_NativeWindow);
+    childWidget->windowHandle()->create();
+    widget.show();
+    QVERIFY(QTest::qWaitForWindowExposed(&widget));
+    widget.windowHandle()->close();
+    widget.show();
+    QVERIFY(QTest::qWaitForWindowExposed(&widget));
+    // Check that the child window inside the window is now visible
+    QVERIFY(childWidget->isVisible());
+
+    // Now explicitly hide the childWidget
+    childWidget->hide();
+    widget.windowHandle()->close();
+    widget.show();
+    QVERIFY(QTest::qWaitForWindowExposed(&widget));
+    QVERIFY(!childWidget->isVisible());
+}
+
 QTEST_MAIN(tst_QWidget)
 #include "tst_qwidget.moc"