[wayland] Improve passing env variables to applications started by KWin

If an env variable is set outside of KWin (e.g. QT_QPA_PLATFORM) we
want KWin to pass the original env variable to the started process and
not pass none instead because it's one of KWin's special changed
variables.

Thus we take the environment before we adjust it and pass that to the
started processes with our own DISPLAY and WAYLAND_DISPLAY added.

main_wayland.cpp

@@ -177,12 +177,11 @@ void ApplicationWayland::continueStartupWithX()
     if (!m_inputMethodServerToStart.isEmpty()) {
         int socket = dup(waylandServer()->createInputMethodConnection());
         if (socket >= 0) {
-            QProcessEnvironment environment = QProcessEnvironment::systemEnvironment();
+            QProcessEnvironment environment = m_environment;
             environment.insert(QStringLiteral("WAYLAND_SOCKET"), QByteArray::number(socket));
             environment.insert(QStringLiteral("QT_QPA_PLATFORM"), QStringLiteral("wayland"));
             environment.remove("DISPLAY");
             environment.remove("WAYLAND_DISPLAY");
-            environment.remove(QStringLiteral("EGL_PLATFORM"));
             QProcess *p = new QProcess(this);
             p->setProcessEnvironment(environment);
             p->start(m_inputMethodServerToStart);
@@ -192,14 +191,8 @@ void ApplicationWayland::continueStartupWithX()
 
     // start the applications passed to us as command line arguments
     if (!m_applicationsToStart.isEmpty()) {
-        QProcessEnvironment environment = QProcessEnvironment::systemEnvironment();
+        QProcessEnvironment environment = m_environment;
-        environment.remove(QStringLiteral("WAYLAND_SOCKET"));
-        environment.remove(QStringLiteral("QT_QPA_PLATFORM"));
-        environment.remove(QStringLiteral("QT_WAYLAND_DISABLE_WINDOWDECORATION"));
-        environment.remove(QStringLiteral("EGL_PLATFORM"));
         environment.insert(QStringLiteral("DISPLAY"), QString::fromUtf8(qgetenv("DISPLAY")));
-        // TODO: maybe create a socket per process?
-        environment.insert(QStringLiteral("WAYLAND_DISPLAY"), waylandServer()->display()->socketName());
         for (const QString &application: m_applicationsToStart) {
             // note: this will kill the started process when we exit
             // this is going to happen anyway as we are the wayland and X server the app connects to
@@ -315,7 +308,7 @@ void ApplicationWayland::startXwaylandServer()
 
     m_xwaylandProcess = new QProcess(kwinApp());
     m_xwaylandProcess->setProgram(QStringLiteral("Xwayland"));
-    QProcessEnvironment env = QProcessEnvironment::systemEnvironment();
+    QProcessEnvironment env = m_environment;
     env.insert("WAYLAND_SOCKET", QByteArray::number(wlfd));
     m_xwaylandProcess->setProcessEnvironment(env);
     m_xwaylandProcess->setArguments({QStringLiteral("-displayfd"),
@@ -427,6 +420,9 @@ KWIN_EXPORT int kdemain(int argc, char * argv[])
     sigaddset(&userSiganls, SIGUSR2);
     pthread_sigmask(SIG_BLOCK, &userSiganls, nullptr);
 
+    QProcessEnvironment environment = QProcessEnvironment::systemEnvironment();
+    environment.insert(QStringLiteral("WAYLAND_DISPLAY"), server->display()->socketName());
+
     // enforce wayland plugin, unfortunately command line switch has precedence
     setenv("QT_QPA_PLATFORM", "wayland", true);
 #if (QT_VERSION < QT_VERSION_CHECK(5, 4, 2))
@@ -440,6 +436,7 @@ KWIN_EXPORT int kdemain(int argc, char * argv[])
     qputenv("QT_WAYLAND_DISABLE_WINDOWDECORATION", "1");
     KWin::ApplicationWayland a(argc, argv);
     a.setupTranslator();
+    a.setProcessStartupEnvironment(environment);
 
     server->setParent(&a);
 

main_wayland.h

@@ -21,6 +21,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #define KWIN_MAIN_WAYLAND_H
 #include "main.h"
 #include <QtCore/private/qeventdispatcher_unix_p.h>
+#include <QProcessEnvironment>
 
 class QProcess;
 
@@ -43,6 +44,9 @@ public:
     void setInputMethodServerToStart(const QString &inputMethodServer) {
         m_inputMethodServerToStart = inputMethodServer;
     }
+    void setProcessStartupEnvironment(const QProcessEnvironment &environment) {
+        m_environment = environment;
+    }
 
     bool notify(QObject *o, QEvent *e) override;
 
@@ -61,6 +65,7 @@ private:
     QStringList m_applicationsToStart;
     QString m_inputMethodServerToStart;
     QProcess *m_xwaylandProcess = nullptr;
+    QProcessEnvironment m_environment;
 };
 
 class EventDispatcher : public QEventDispatcherUNIX