Fix child popup palette inheritance

Qt Quick Controls Popups are always top-level popups, even if declared
as a child of another popup. Therefore, e.g. a font set on a parent
popup should not propagate to a child popup. The same behavior applies
to palettes, but we regressed with this in
1875ad7f92 and/or
31f5c21ddb.

This patch fixes the regression by returning the window's palette in
QQuickPaletteProviderPrivateBase<I, Impl>::parentPalette() if I is
a QQuickPopup.

Fixes: QTBUG-115707
Change-Id: Ib89852787dd45e3edc9e846b6c182340c052f0fd
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@qt.io>
(cherry picked from commit 950cd5888e)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/quick/items/qquickpaletteproviderprivatebase_p.h

@@ -230,9 +230,9 @@ template<class Impl, class I> decltype(auto) getPrivateImpl(I &t) { return Impl:
 template <class T>
 decltype(auto) getPrivate(T &item)
 {
-    if constexpr (std::is_same_v<T, QQuickWindow>) {
+    if constexpr (std::is_base_of_v<T, QQuickWindow>) {
         return getPrivateImpl<QQuickWindowPrivate>(item);
-    } else if constexpr (std::is_same_v<T, QQuickItem>) {
+    } else if constexpr (std::is_base_of_v<T, QQuickItem>) {
         return getPrivateImpl<QQuickItemPrivate>(item);
     } else {
         static_assert (dependent_false<T>::value, "Extend please.");
@@ -257,12 +257,15 @@ template<class I, class Impl>
 QPalette QQuickPaletteProviderPrivateBase<I, Impl>::parentPalette(const QPalette &fallbackPalette) const
 {
     if constexpr (!isRootWindow<I>()) {
-        for (auto parentItem = itemWithPalette()->parentItem(); parentItem;
-             parentItem = parentItem->parentItem()) {
+        // Popups should always inherit from their window, even child popups: QTBUG-115707.
+        if (!std::is_base_of_v<QQuickPopup, I>) {
+            for (auto parentItem = itemWithPalette()->parentItem(); parentItem;
+                 parentItem = parentItem->parentItem()) {
 
-            // Don't allocate a new palette here. Use only if it's already pre allocated
-            if (parentItem && getPrivate(*parentItem)->providesPalette()) {
-                return getPrivate(*parentItem)->palette()->toQPalette();
+                // Don't allocate a new palette here. Use only if it's already pre allocated
+                if (parentItem && getPrivate(*parentItem)->providesPalette()) {
+                    return getPrivate(*parentItem)->palette()->toQPalette();
+                }
             }
         }
 
@@ -279,7 +282,7 @@ const QQuickItem* rootItem(const I &item)
 {
     if constexpr (isRootWindow<I>()) {
         return item.contentItem();
-    } else if constexpr (std::is_same_v<QQuickPopup, I>) {
+    } else if constexpr (std::is_base_of_v<QQuickPopup, I>) {
         return nullptr;
     } else {
         return &item;

tests/auto/quickcontrols/palette/data/childPopupInheritance.qml

@@ -0,0 +1,40 @@
+// Copyright (C) 2023 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
+
+import QtQuick
+import QtQuick.Controls
+
+ApplicationWindow {
+    id: window
+
+    Popup {
+        id: parentPopup
+        objectName: "parentPopup"
+        palette.windowText: "#ffdead"
+
+        Label {
+            text: "parentPopupLabel"
+            objectName: text
+        }
+
+        Popup {
+            id: childPopup
+            objectName: "childPopup"
+
+            Label {
+                text: "childPopupLabel"
+                objectName: text
+            }
+
+            Popup {
+                id: grandchildPopup
+                objectName: "grandchildPopup"
+
+                Label {
+                    text: "grandchildPopupLabel"
+                    objectName: text
+                }
+            }
+        }
+    }
+}

tests/auto/quickcontrols/palette/tst_palette.cpp

@@ -7,6 +7,7 @@
 #include <QtQml/qqmlengine.h>
 #include <QtQml/qqmlcomponent.h>
 #include <QtQuickTestUtils/private/qmlutils_p.h>
+#include <QtQuickControlsTestUtils/private/controlstestutils_p.h>
 #include <QtQuick/private/qquickitem_p.h>
 #include <QtQuickTemplates2/private/qquickapplicationwindow_p.h>
 #include <QtQuickTemplates2/private/qquickcontrol_p.h>
@@ -17,7 +18,7 @@
 #include <QtQuickTemplates2/private/qquickbutton_p.h>
 #include <QtQuickControls2/qquickstyle.h>
 
-//using namespace QQuickVisualTestUtils;
+using namespace QQuickControlsTestUtils;
 
 // Need a more descriptive failure message: QTBUG-87039
 #define COMPARE_PALETTES(actualPalette, expectedPalette) \
@@ -40,6 +41,7 @@ private slots:
 
     void inheritance_data();
     void inheritance();
+    void childPopupInheritance();
 
     void defaultPalette_data();
     void defaultPalette();
@@ -203,6 +205,40 @@ void tst_palette::inheritance()
     QCOMPARE(grandChildPalette->window(), windowPalette->window());
 }
 
+// The child popups in inheritance() don't test actual nested child popups,
+// only popups that are children of items and the items within those popups.
+// We need to specifically test this to prevent QTBUG-115707 from happening again.
+void tst_palette::childPopupInheritance()
+{
+    QQuickControlsApplicationHelper helper(this, QLatin1String("childPopupInheritance.qml"));
+    QVERIFY2(helper.ready, helper.failureMessage());
+
+    const auto *windowPrivate = QQuickWindowPrivate::get(helper.window);
+    const auto windowsWindowTextColor = windowPrivate->palette()->toQPalette().color(QPalette::WindowText);
+
+    // parentPopup sets windowText explicitly, so its label should use that color.
+    auto *parentPopup = helper.appWindow->findChild<QQuickPopup *>("parentPopup");
+    QVERIFY(parentPopup);
+    parentPopup->open();
+    QTRY_VERIFY(parentPopup->isOpened());
+    auto *parentPopupLabel = helper.appWindow->findChild<QObject *>("parentPopupLabel");
+    QVERIFY(parentPopupLabel);
+    QCOMPARE(parentPopupLabel->property("color").value<QColor>(), "#ffdead");
+
+    // All other child popups don't set anything explicitly, and should inherit from their window.
+    auto *childPopup = helper.appWindow->findChild<QQuickPopup *>("childPopup");
+    QVERIFY(childPopup);
+    auto *childPopupLabel = helper.appWindow->findChild<QObject *>("childPopupLabel");
+    QVERIFY(childPopupLabel);
+    QCOMPARE(childPopupLabel->property("color").value<QColor>(), windowsWindowTextColor);
+
+    auto *grandchildPopup = helper.appWindow->findChild<QQuickPopup *>("grandchildPopup");
+    QVERIFY(grandchildPopup);
+    auto *grandchildPopupLabel = helper.appWindow->findChild<QObject *>("grandchildPopupLabel");
+    QVERIFY(grandchildPopupLabel);
+    QCOMPARE(grandchildPopupLabel->property("color").value<QColor>(), windowsWindowTextColor);
+}
+
 class TestTheme : public QQuickTheme
 {
 public: