Add palette() and further hints to QtGui/QPlatformTheme.

- Move palette() from deprecated QtWidgets/QGuiPlatformPlugin
  to  QtGui/QPlatformTheme, Make it return a const * since
  QPalette does not have isNull().
- Initialize QGuiApplication::palette() and
  QApplication::systemPalette() from it.
- Do not initialize QPalette from QGuiApplication::palette()
  unless app_pal is non-null (default to Qt::black if it is 0).
  This avoids initialization order crashes/recursions in the
  QPA plugin. Streamline initialization function.
- Remove styleName(), systemIconThemeName() and iconSearchPaths()
  from QGuiPlatformPlugin and re-add them as
  QPlatformTheme::themeHint().
- Remove styleHint() from QGuiPlatformPlugin, add it to
  QPlatformTheme::themeHint().
- Add UNIX themes with factory function (Generic,
  KDE, Gnome), taking it from Qt 4.8 code (stripping the
  KDE 3 code).
- Implement Windows palettes.

Task-number: QTBUG-24204

Change-Id: Ie27ec035df4f84c42deaffc4816b2e53ce705462
Reviewed-by: Morten Johan Sørvig <morten.sorvig@nokia.com>

2 files changed, 8 insertions, 6 deletions

diff --git a/src/platformsupport/services/genericunix/qgenericunixservices.cpp b/src/platformsupport/services/genericunix/qgenericunixservices.cpp
index 3c10fb63f6..34f46e4e6e 100644
--- a/src/platformsupport/services/genericunix/qgenericunixservices.cpp
+++ b/src/platformsupport/services/genericunix/qgenericunixservices.cpp
@@ -122,9 +122,10 @@ static inline bool launch(const QString &launcher, const QUrl &url)
     return ok;
 }
 
-QGenericUnixServices::QGenericUnixServices() :
-    m_desktopEnvironment(detectDesktopEnvironment())
+QGenericUnixServices::DesktopEnvironment QGenericUnixServices::desktopEnvironment()
 {
+    static const DesktopEnvironment result = detectDesktopEnvironment();
+    return result;
 }
 
 bool QGenericUnixServices::openUrl(const QUrl &url)
@@ -132,7 +133,7 @@ bool QGenericUnixServices::openUrl(const QUrl &url)
     if (url.scheme() == QStringLiteral("mailto"))
         return openDocument(url);
 
-    if (m_webBrowser.isEmpty() && !detectWebBrowser(m_desktopEnvironment, true, &m_webBrowser)) {
+    if (m_webBrowser.isEmpty() && !detectWebBrowser(desktopEnvironment(), true, &m_webBrowser)) {
         qWarning("%s: Unable to detect a web browser to launch '%s'", Q_FUNC_INFO, qPrintable(url.toString()));
         return false;
     }
@@ -141,7 +142,7 @@ bool QGenericUnixServices::openUrl(const QUrl &url)
 
 bool QGenericUnixServices::openDocument(const QUrl &url)
 {
-    if (m_documentLauncher.isEmpty() && !detectWebBrowser(m_desktopEnvironment, false, &m_documentLauncher)) {
+    if (m_documentLauncher.isEmpty() && !detectWebBrowser(desktopEnvironment(), false, &m_documentLauncher)) {
         qWarning("%s: Unable to detect a launcher for '%s'", Q_FUNC_INFO, qPrintable(url.toString()));
         return false;
     }
diff --git a/src/platformsupport/services/genericunix/qgenericunixservices_p.h b/src/platformsupport/services/genericunix/qgenericunixservices_p.h
index 48b790a5b8..3923a45f89 100644
--- a/src/platformsupport/services/genericunix/qgenericunixservices_p.h
+++ b/src/platformsupport/services/genericunix/qgenericunixservices_p.h
@@ -58,13 +58,14 @@ public:
         DE_GNOME
     };
 
-    QGenericUnixServices();
+    QGenericUnixServices() {}
+
+    static DesktopEnvironment desktopEnvironment();
 
     virtual bool openUrl(const QUrl &url);
     virtual bool openDocument(const QUrl &url);
 
 private:
-    const DesktopEnvironment m_desktopEnvironment;
     QString m_webBrowser;
     QString m_documentLauncher;
 };