Fix QQuickTheme::font() and palette()

Respect fonts and palettes from :/qtquickcontrols2.conf, but don't
blatantly override the platform fonts and palettes with null values
if the fonts and palettes are not set in :/qtquickcontrols2.conf.

Even though fonts and palettes have technically same problem, testing
the system palette is hard with 5.11 since QQuickDefaultTheme is a
platform proxy theme and provides a custom system palette. It should
be possible to have tst_palette::systemPalette() in dev, though, where
we have removed the inheritance between QQuickTheme and QPlatformTheme.

Task-number: QTBUG-66430
Change-Id: I6dfe678ccdc7e3990320c120612cfcc68723264d
Reviewed-by: Mitch Curtis <mitch.curtis@qt.io>

2 files changed, 42 insertions, 4 deletions

diff --git a/src/quickcontrols2/qquicktheme.cpp b/src/quickcontrols2/qquicktheme.cpp
index 06a66bfd..3643e975 100644
--- a/src/quickcontrols2/qquicktheme.cpp
+++ b/src/quickcontrols2/qquicktheme.cpp
@@ -134,14 +134,16 @@ QQuickTheme::QQuickTheme(const QString &style)
 
 const QFont *QQuickTheme::font(Font type) const
 {
-    Q_UNUSED(type);
-    return m_styleFont.data();
+    if (m_styleFont)
+        return m_styleFont.data();
+    return QQuickProxyTheme::font(type);
 }
 
 const QPalette *QQuickTheme::palette(Palette type) const
 {
-    Q_UNUSED(type);
-    return m_stylePalette.data();
+    if (m_stylePalette)
+        return m_stylePalette.data();
+    return QQuickProxyTheme::palette(type);
 }
 
 QFont QQuickTheme::resolveFont(const QFont &font) const
diff --git a/tests/auto/font/tst_font.cpp b/tests/auto/font/tst_font.cpp
index 660f4baf..75942286 100644
--- a/tests/auto/font/tst_font.cpp
+++ b/tests/auto/font/tst_font.cpp
@@ -54,6 +54,8 @@ class tst_font : public QQmlDataTest
     Q_OBJECT
 
 private slots:
+    void systemFont();
+
     void font_data();
     void font();
 
@@ -67,6 +69,40 @@ private slots:
     void listView();
 };
 
+static QFont testFont()
+{
+    QQmlEngine engine;
+    QQmlComponent component(&engine);
+    component.setData("import QtQuick 2.0; import QtQuick.Controls 2.0; Text { }", QUrl());
+
+    QScopedPointer<QObject> object(component.create());
+    Q_ASSERT_X(!object.isNull(), "testFont", qPrintable(component.errorString()));
+
+    QVariant var = object->property("font");
+    Q_ASSERT_X(var.isValid(), "testFont", var.typeName());
+    return var.value<QFont>();
+}
+
+void tst_font::systemFont()
+{
+    const QFont *originalSystemFont = QGuiApplicationPrivate::platformTheme()->font(QPlatformTheme::SystemFont);
+    if (!originalSystemFont)
+        QSKIP("Cannot test the system font on a minimal platform");
+
+    const QFont fontBefore = testFont();
+    QCOMPARE(fontBefore, *originalSystemFont);
+
+    qmlClearTypeRegistrations();
+    delete QGuiApplicationPrivate::app_font;
+    QGuiApplicationPrivate::app_font = nullptr;
+
+    const QFont appFont = QGuiApplication::font();
+    QCOMPARE(appFont, *originalSystemFont);
+
+    const QFont fontAfter = testFont();
+    QCOMPARE(fontAfter, *originalSystemFont);
+}
+
 void tst_font::font_data()
 {
     QTest::addColumn<QString>("testFile");