Detect Unity by checking XDG_CURRENT_DESKTOP and use Gnome theme.

Fallback to Gtk for unknown desktops, which should be suitable
for most cases like XFCE.

Task-number: QTCREATORBUG-8254

Change-Id: Iaf9959f75852e03a83b5af7d0dead01ef657d678
Reviewed-by: Frederik Gladhorn <frederik.gladhorn@digia.com>

2 files changed, 7 insertions, 2 deletions

diff --git a/src/platformsupport/services/genericunix/qgenericunixservices.cpp b/src/platformsupport/services/genericunix/qgenericunixservices.cpp
index f6bf8608d1..7d0145e61d 100644
--- a/src/platformsupport/services/genericunix/qgenericunixservices.cpp
+++ b/src/platformsupport/services/genericunix/qgenericunixservices.cpp
@@ -56,6 +56,10 @@ static inline QByteArray detectDesktopEnvironment()
 {
     if (!qEnvironmentVariableIsEmpty("KDE_FULL_SESSION"))
         return QByteArray("KDE");
+    // Check Unity first, whose older versions also have "GNOME_DESKTOP_SESSION_ID" set.
+    const QByteArray xdgCurrentDesktop = qgetenv("XDG_CURRENT_DESKTOP");
+    if (xdgCurrentDesktop == "Unity")
+        return QByteArrayLiteral("UNITY");
     // GNOME_DESKTOP_SESSION_ID is deprecated for some reason, but still check it
     if (qgetenv("DESKTOP_SESSION") == "gnome" || !qEnvironmentVariableIsEmpty("GNOME_DESKTOP_SESSION_ID"))
         return QByteArray("GNOME");
diff --git a/src/platformsupport/themes/genericunix/qgenericunixthemes.cpp b/src/platformsupport/themes/genericunix/qgenericunixthemes.cpp
index a39f26efc8..d773bc8c8e 100644
--- a/src/platformsupport/themes/genericunix/qgenericunixthemes.cpp
+++ b/src/platformsupport/themes/genericunix/qgenericunixthemes.cpp
@@ -420,11 +420,12 @@ QStringList QGenericUnixTheme::themeNames()
 {
     QStringList result;
     if (QGuiApplication::desktopSettingsAware()) {
-        if (QGuiApplicationPrivate::platformIntegration()->services()->desktopEnvironment() == QByteArray("KDE")) {
+        const QByteArray desktopEnvironment = QGuiApplicationPrivate::platformIntegration()->services()->desktopEnvironment();
+        if (desktopEnvironment == QByteArrayLiteral("KDE")) {
 #ifndef QT_NO_SETTINGS
             result.push_back(QLatin1String(QKdeTheme::name));
 #endif
-        } else if (QGuiApplicationPrivate::platformIntegration()->services()->desktopEnvironment() == QByteArray("GNOME")) {
+        } else { // Gnome, Unity, other Gtk-based desktops like XFCE.
             result.push_back(QLatin1String(QGnomeTheme::name));
         }
         const QString session = QString::fromLocal8Bit(qgetenv("DESKTOP_SESSION"));