wayland: Query pkg-config if Xwayland supports listenfd

-listen <fd> option is deprecated in favor of the -listenfd option. This
change makes kwin query whether Xwayland supports the -listenfd option
at build time. If the pkg-config file is missing, we'll use the old listen
option.

CMakeLists.txt

@@ -294,6 +294,7 @@ set_package_properties(Xwayland PROPERTIES
     TYPE RUNTIME
     PURPOSE "Needed for running kwin_wayland"
 )
+set(HAVE_XWAYLAND_LISTENFD ${Xwayland_HAVE_LISTENFD})
 
 find_package(Libcap)
 set_package_properties(Libcap PROPERTIES

cmake/modules/FindXwayland.cmake

@@ -1,13 +1,39 @@
+#.rst:
+# FindXwayland
+# -------
+#
+# Try to find Xwayland on a Unix system.
+#
+# This will define the following variables:
+#
+# ``Xwayland_FOUND``
+#     True if (the requested version of) Xwayland is available
+# ``Xwayland_VERSION``
+#     The version of Xwayland
+# ``Xwayland_HAVE_LISTENFD``
+#     True if (the requested version of) Xwayland has -listenfd option
+
 #=============================================================================
 # SPDX-FileCopyrightText: 2016 Martin Gräßlin <mgraesslin@kde.org>
+# SPDX-FileCopyrightText: 2021 Vlad Zahorodnii <vlad.zahorodnii@kde.org>
 #
 # SPDX-License-Identifier: BSD-3-Clause
 #=============================================================================
+
+find_package(PkgConfig)
+pkg_check_modules(PKG_xwayland QUIET xwayland)
+
+set(Xwayland_VERSION ${PKG_xwayland_VERSION})
+pkg_get_variable(Xwayland_HAVE_LISTENFD xwayland have_listenfd)
+
 find_program(Xwayland_EXECUTABLE NAMES Xwayland)
 find_package_handle_standard_args(Xwayland
-    FOUND_VAR
-        Xwayland_FOUND
-    REQUIRED_VARS
-        Xwayland_EXECUTABLE
+    FOUND_VAR Xwayland_FOUND
+    REQUIRED_VARS Xwayland_EXECUTABLE
+    VERSION_VAR Xwayland_VERSION
+)
+mark_as_advanced(
+    Xwayland_EXECUTABLE
+    Xwayland_HAVE_LISTENFD
+    Xwayland_VERSION
 )
-mark_as_advanced(Xwayland_EXECUTABLE)

src/config-kwin.h.cmake

@@ -48,3 +48,5 @@
 #endif
 
 #cmakedefine PipeWire_FOUND 1
+
+#cmakedefine HAVE_XWAYLAND_LISTENFD

src/xwl/xwayland.cpp

@@ -215,6 +215,22 @@ bool Xwayland::startInternal()
 
     m_xcbConnectionFd = sx[0];
 
+    QStringList arguments {
+        m_socket->name(),
+        QStringLiteral("-displayfd"), QString::number(pipeFds[1]),
+        QStringLiteral("-rootless"),
+        QStringLiteral("-wm"), QString::number(fd),
+        QStringLiteral("-auth"), m_authorityFile.fileName(),
+    };
+
+#if defined(HAVE_XWAYLAND_LISTENFD)
+    arguments << QStringLiteral("-listenfd") << QString::number(abstractSocket)
+              << QStringLiteral("-listenfd") << QString::number(unixSocket);
+#else
+    arguments << QStringLiteral("-listen") << QString::number(abstractSocket)
+              << QStringLiteral("-listen") << QString::number(unixSocket);
+#endif
+
     m_xwaylandProcess = new Process(this);
     m_xwaylandProcess->setProcessChannelMode(QProcess::ForwardedErrorChannel);
     m_xwaylandProcess->setProgram(QStringLiteral("Xwayland"));
@@ -225,13 +241,7 @@ bool Xwayland::startInternal()
         env.insert("WAYLAND_DEBUG", QByteArrayLiteral("1"));
     }
     m_xwaylandProcess->setProcessEnvironment(env);
-    m_xwaylandProcess->setArguments({m_socket->name(),
-                           QStringLiteral("-displayfd"), QString::number(pipeFds[1]),
-                           QStringLiteral("-rootless"),
-                           QStringLiteral("-wm"), QString::number(fd),
-                           QStringLiteral("-auth"), m_authorityFile.fileName(),
-                           QStringLiteral("-listen"), QString::number(abstractSocket),
-                           QStringLiteral("-listen"), QString::number(unixSocket)});
+    m_xwaylandProcess->setArguments(arguments);
     connect(m_xwaylandProcess, &QProcess::errorOccurred, this, &Xwayland::handleXwaylandError);
     connect(m_xwaylandProcess, QOverload<int, QProcess::ExitStatus>::of(&QProcess::finished),
             this, &Xwayland::handleXwaylandFinished);