Enable checking for whether the system palette was explicitly set

In order to obey a palette set globally on QApplication, an application
attribute for checking if it's set at all is added.

Task-number: QTBUG-39800
Change-Id: I26b965e6e18e0e1ca4df03cf343b3527df3636b2
Reviewed-by: J-P Nurmi <jpnurmi@theqtcompany.com>
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@theqtcompany.com>

src/corelib/global/qnamespace.h

@@ -492,6 +492,7 @@ public:
         AA_UseOpenGLES = 16,
         AA_UseSoftwareOpenGL = 17,
         AA_ShareOpenGLContexts = 18,
+        AA_SetPalette = 19,
 
         // Add new attributes before this line
         AA_AttributeCount

src/corelib/global/qnamespace.qdoc

@@ -194,6 +194,9 @@
            instances that belong to different top-level windows. This value has
            been added in Qt 5.4.
 
+    \value AA_SetPalette Indicates whether a palette was explicitly set on the
+           QApplication/QGuiApplication. This value has been added in Qt 5.5.
+
     The following values are obsolete:
 
     \value AA_ImmediateWidgetCreation This attribute is no longer fully

src/gui/kernel/qguiapplication.cpp

@@ -2757,6 +2757,7 @@ void QGuiApplication::setPalette(const QPalette &pal)
     else
         *QGuiApplicationPrivate::app_pal = pal;
     applicationResourceFlags |= ApplicationPaletteExplicitlySet;
+    QCoreApplication::setAttribute(Qt::AA_SetPalette);
     emit qGuiApp->paletteChanged(*QGuiApplicationPrivate::app_pal);
 }
 

src/widgets/kernel/qapplication.cpp

@@ -1508,6 +1508,7 @@ void QApplicationPrivate::setPalette_helper(const QPalette &palette, const char*
             QApplicationPrivate::set_pal = new QPalette(palette);
         else
             *QApplicationPrivate::set_pal = palette;
+        QCoreApplication::setAttribute(Qt::AA_SetPalette);
     }
 }
 

tests/auto/gui/kernel/qguiapplication/tst_qguiapplication.cpp

@@ -76,6 +76,7 @@ private slots:
     void genericPluginsAndWindowSystemEvents();
     void layoutDirection();
     void globalShareContext();
+    void testSetPaletteAttribute();
 
     void staticFunctions();
 
@@ -968,6 +969,22 @@ void tst_QGuiApplication::globalShareContext()
 #endif
 }
 
+void tst_QGuiApplication::testSetPaletteAttribute()
+{
+    QCoreApplication::setAttribute(Qt::AA_SetPalette, false);
+    int argc = 1;
+    char *argv[] = { const_cast<char*>("tst_qguiapplication") };
+
+    QGuiApplication app(argc, argv);
+
+    QVERIFY(!QCoreApplication::testAttribute(Qt::AA_SetPalette));
+    QPalette palette;
+    palette.setColor(QPalette::Foreground, Qt::red);
+    QGuiApplication::setPalette(palette);
+
+    QVERIFY(QCoreApplication::testAttribute(Qt::AA_SetPalette));
+}
+
 // Test that static functions do not crash if there is no application instance.
 void tst_QGuiApplication::staticFunctions()
 {