Fix fallback styles overwriting themes

In Qt 5, QtQuickControls2Plugin::registerTypes() was responsible for
calling initializeTheme() on each style plugin. Now that we delegate
more work to the QML engine, each style plugin calls initializeTheme()
via registerTypes().

To avoid fallback styles overwriting font and palette data set by the
current style, we need to check if the theme has been intialized before
calling initializeTheme(). To do this, we add a static
"themeInitialized" bool that QQuickStylePlugin sets to true after
calling intializeTheme() for the first time. It checks this value and
avoids calling intializeTheme() if it's true.

We also need to make QQuickStylePlugin ensure that the theme it's
initializing belongs to the current style.

Fixes: QTBUG-86303
Change-Id: Ie65e646677c78622829f4949c41cb79204cf5786
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@qt.io>

1 files changed, 46 insertions, 1 deletions

diff --git a/tests/auto/styleimports/tst_styleimports.cpp b/tests/auto/styleimports/tst_styleimports.cpp
index 8b47dee7..fa524098 100644
--- a/tests/auto/styleimports/tst_styleimports.cpp
+++ b/tests/auto/styleimports/tst_styleimports.cpp
@@ -43,6 +43,7 @@
 #include <QtQuick/qquickwindow.h>
 #include <QtQuickControls2/qquickstyle.h>
 #include <QtQuickControls2/private/qquickstyle_p.h>
+#include <QtQuickControls2Impl/private/qquickiconlabel_p.h>
 
 #include "../shared/util.h"
 
@@ -62,6 +63,9 @@ private slots:
 
     void importStyleWithoutControls_data();
     void importStyleWithoutControls();
+
+    void fallbackStyleShouldNotOverwriteTheme_data();
+    void fallbackStyleShouldNotOverwriteTheme();
 };
 
 void tst_StyleImports::initTestCase()
@@ -151,6 +155,7 @@ void tst_StyleImports::select()
     QQuickStyle::setFallbackStyle(fallback);
 
     QQmlEngine engine;
+    engine.addImportPath(QLatin1String(":/"));
     engine.addImportPath(directory());
     engine.addImportPath(dataDirectory());
     QQmlComponent component(&engine);
@@ -185,7 +190,7 @@ void tst_StyleImports::platformSelectors()
 
     QQmlApplicationEngine engine;
     engine.addImportPath(dataDirectory());
-    engine.load(testFileUrl("platformSelectors.qml"));
+    engine.load(testFileUrl("applicationWindowWithButton.qml"));
     QQuickWindow *window = qobject_cast<QQuickWindow*>(engine.rootObjects().first());
     QVERIFY(window);
 
@@ -241,6 +246,46 @@ void tst_StyleImports::importStyleWithoutControls()
     QTRY_VERIFY(success);
 }
 
+void tst_StyleImports::fallbackStyleShouldNotOverwriteTheme_data()
+{
+    QTest::addColumn<QString>("style");
+    QTest::addColumn<QString>("fallbackStyle");
+    QTest::addColumn<QColor>("expectedContentItemColor");
+
+    QTest::addRow("style=Fusion,fallbackStyle=Material")
+        << QString::fromLatin1("Fusion") << QString::fromLatin1("Material") << QColor::fromRgb(0x252525);
+    QTest::addRow("style=ResourceStyle,fallbackStyle=Material")
+        << QString::fromLatin1("ResourceStyle") << QString::fromLatin1("Material") << QColor("salmon");
+}
+
+void tst_StyleImports::fallbackStyleShouldNotOverwriteTheme()
+{
+    QFETCH(QString, style);
+    QFETCH(QString, fallbackStyle);
+    QFETCH(QColor, expectedContentItemColor);
+
+    QQuickStyle::setStyle(style);
+    QQuickStyle::setFallbackStyle(fallbackStyle);
+
+    QQmlApplicationEngine engine;
+    engine.addImportPath(QLatin1String(":/"));
+    engine.addImportPath(dataDirectory());
+    engine.load(testFileUrl("applicationWindowWithButton.qml"));
+    QVERIFY(!engine.rootObjects().isEmpty());
+    QQuickWindow *window = qobject_cast<QQuickWindow*>(engine.rootObjects().first());
+    QVERIFY(window);
+
+    QObject *button = window->property("button").value<QObject*>();
+    QVERIFY(button);
+
+    QQuickIconLabel *contentItem = button->property("contentItem").value<QQuickIconLabel*>();
+    QVERIFY(contentItem);
+
+    // For example: the Fusion style provides Button.qml, so the Button's text color
+    // should be that of QPalette::ButtonText from QQuickFusionTheme.
+    QCOMPARE(contentItem->color(), expectedContentItemColor);
+}
+
 QTEST_MAIN(tst_StyleImports)
 
 #include "tst_styleimports.moc"