Set WAYLAND_DISPLAY before starting wayland server

Apparently, zink (when calling gbm_create_device()) may connect to the
wayland server if the WAYLAND_DISPLAY envvar is set and deadlock.


(cherry picked from commit d802b7c32c)

Co-authored-by: Vlad Zahorodnii <vlad.zahorodnii@kde.org>

src/main_wayland.cpp

@@ -593,11 +593,6 @@ int main(int argc, char *argv[])
     }
 
     QObject::connect(&a, &KWin::Application::workspaceCreated, server, &KWin::WaylandServer::initWorkspace);
-    if (!server->socketName().isEmpty()) {
-        environment.insert(QStringLiteral("WAYLAND_DISPLAY"), server->socketName());
-        qputenv("WAYLAND_DISPLAY", server->socketName().toUtf8());
-    }
-    a.setProcessStartupEnvironment(environment);
 
 #if KWIN_BUILD_X11
     if (parser.isSet(xwaylandOption)) {
@@ -627,6 +622,7 @@ int main(int argc, char *argv[])
     }
 #endif
 
+    a.setProcessStartupEnvironment(environment);
     a.setApplicationsToStart(parser.positionalArguments());
     a.setInputMethodServerToStart(parser.value(inputMethodOption));
     a.start();

src/wayland_server.cpp

@@ -318,6 +318,13 @@ void WaylandServer::handleOutputDisabled(Output *output)
 
 bool WaylandServer::start()
 {
+    QProcessEnvironment environment = kwinApp()->processStartupEnvironment();
+    if (!socketName().isEmpty()) {
+        environment.insert(QStringLiteral("WAYLAND_DISPLAY"), socketName());
+        qputenv("WAYLAND_DISPLAY", socketName().toUtf8());
+    }
+    kwinApp()->setProcessStartupEnvironment(environment);
+
     return m_display->start();
 }