Refactor theme plugin loading.

In the old implementation, the QPlatformIntegration was asked
for the theme first, so there was no way of overriding that
by a custom plugin. Also, there was a memory leak in case
the platform theme was actually created by a plugin.

QGuiApplication now asks the QPlatformIntegration for a list
of potential theme names first, tries to load them using
the plugin loader and finally invokes a factory method of
QPlatformIntegration in case that fails. The theme is now
owned by QGuiApplication.

In the XCB plugin, the environment variable DESKTOP_SESSION
is queried and appended to the list of themes, making it possible
to load plugins for other session types.

Change-Id: I1a4b4e061815bca16c65b23e591bb7563a3e44e2
Reviewed-by: Samuel Rødal <samuel.rodal@nokia.com>

4 files changed, 17 insertions, 4 deletions

diff --git a/src/plugins/platforms/cocoa/qcocoaintegration.h b/src/plugins/platforms/cocoa/qcocoaintegration.h
index 2389fc2a55..9248df0d37 100644
--- a/src/plugins/platforms/cocoa/qcocoaintegration.h
+++ b/src/plugins/platforms/cocoa/qcocoaintegration.h
@@ -93,7 +93,9 @@ public:
     QPlatformAccessibility *accessibility() const;
     QPlatformDrag *drag() const;
 
-    QPlatformTheme *platformTheme() const;
+    QStringList themeNames() const;
+    QPlatformTheme *createPlatformTheme(const QString &name) const;
+
 private:
 
     QScopedPointer<QPlatformFontDatabase> mFontDb;
diff --git a/src/plugins/platforms/cocoa/qcocoaintegration.mm b/src/plugins/platforms/cocoa/qcocoaintegration.mm
index d490495be4..96027e0925 100644
--- a/src/plugins/platforms/cocoa/qcocoaintegration.mm
+++ b/src/plugins/platforms/cocoa/qcocoaintegration.mm
@@ -93,7 +93,6 @@ QCocoaIntegration::QCocoaIntegration()
     , mEventDispatcher(new QCocoaEventDispatcher())
     , mInputContext(new QCocoaInputContext)
     , mAccessibility(new QPlatformAccessibility)
-    , mPlatformTheme(new QCocoaTheme)
     , mCocoaDrag(new QCocoaDrag)
 {
     QCocoaAutoReleasePool pool;
@@ -212,9 +211,16 @@ QPlatformDrag *QCocoaIntegration::drag() const
     return mCocoaDrag.data();
 }
 
-QPlatformTheme *QCocoaIntegration::platformTheme() const
+QStringList QCocoaIntegration::themeNames() const
 {
-    return mPlatformTheme.data();
+    return QStringList(QLatin1String(QCocoaTheme::name));
+}
+
+QPlatformTheme *QCocoaIntegration::createPlatformTheme(const QString &name) const
+{
+    if (name == QLatin1String(QCocoaTheme::name))
+        return new QCocoaTheme;
+    return QPlatformIntegration::createPlatformTheme(name);
 }
 
 QT_END_NAMESPACE
diff --git a/src/plugins/platforms/cocoa/qcocoatheme.h b/src/plugins/platforms/cocoa/qcocoatheme.h
index 030db1822c..5cb6f7437d 100644
--- a/src/plugins/platforms/cocoa/qcocoatheme.h
+++ b/src/plugins/platforms/cocoa/qcocoatheme.h
@@ -64,6 +64,9 @@ public:
     const QFont *font(Font type = SystemFont) const;
 
     QVariant themeHint(ThemeHint hint) const;
+
+    static const char *name;
+
 private:
     mutable QPalette *m_systemPalette;
     mutable QHash<QPlatformTheme::Palette, QPalette*> m_palettes;
diff --git a/src/plugins/platforms/cocoa/qcocoatheme.mm b/src/plugins/platforms/cocoa/qcocoatheme.mm
index 8ec6e3801e..d17ee30096 100644
--- a/src/plugins/platforms/cocoa/qcocoatheme.mm
+++ b/src/plugins/platforms/cocoa/qcocoatheme.mm
@@ -49,6 +49,8 @@
 
 QT_BEGIN_NAMESPACE
 
+const char *QCocoaTheme::name = "cocoa";
+
 QCocoaTheme::QCocoaTheme()
     :m_systemPalette(0)
 {