Expose a method to allow closing windows on shutdown.

This allows Plasma to gracefully close windows on shutdown by sending
xdg_toplevel.close. If after 10 seconds windows are still open because
they prompt for unsaved changes or similar cases, a notification is
shown to either prompt or logout regardless.
CCBUG: 461176

src/org.kde.KWin.Session.xml

@@ -22,6 +22,9 @@
       <!-- Shutdown kwin at the end of the session -->
       <method name="quit">
       </method>
+      <method name="closeWaylandWindows">
+          <arg type="b" direction="out" />
+      </method>
    </interface>
 </node>
 

src/sm.cpp

@@ -16,13 +16,22 @@
 #include <unistd.h>
 
 #include "virtualdesktops.h"
+#include "wayland_server.h"
 #include "workspace.h"
 #include "x11window.h"
+#include "xdgshellwindow.h"
 #include <QDebug>
+
 #include <QSessionManager>
+#if KWIN_BUILD_NOTIFICATIONS
+#include <KLocalizedString>
+#include <KNotification>
+#include <KService>
+#endif
 
 #include "sessionadaptor.h"
-#include <QDBusConnection>
+
+using namespace Qt::StringLiterals;
 
 namespace KWin
 {
@@ -385,6 +394,7 @@ void SessionManager::setState(SessionState state)
             client->setSessionActivityOverride(false);
         });
     }
+
     m_sessionState = state;
     Q_EMIT stateChanged();
 }
@@ -401,6 +411,78 @@ void SessionManager::finishSaveSession(const QString &name)
     storeSession(name, SMSavePhase2);
 }
 
+bool SessionManager::closeWaylandWindows()
+{
+    Q_ASSERT(calledFromDBus());
+    if (!waylandServer()) {
+        return true;
+    }
+
+    if (m_closingWindowsGuard) {
+        sendErrorReply(QDBusError::Failed, u"Operation already in progress"_s);
+        return false;
+    }
+
+    m_closingWindowsGuard = std::make_unique<QObject>();
+    qCDebug(KWIN_CORE) << "Closing windows";
+
+    auto dbusMessage = message();
+    setDelayedReply(true);
+
+    const auto windows = workspace()->windows();
+    m_pendingWindows.clear();
+    m_pendingWindows.reserve(windows.size());
+    for (const auto window : windows) {
+        if (auto toplevelWindow = qobject_cast<XdgToplevelWindow *>(window)) {
+            connect(toplevelWindow, &XdgToplevelWindow::closed, m_closingWindowsGuard.get(), [this, toplevelWindow, dbusMessage] {
+                m_pendingWindows.removeOne(toplevelWindow);
+                if (m_pendingWindows.empty()) {
+                    m_closeTimer.stop();
+                    m_closingWindowsGuard.reset();
+                    QDBusConnection::sessionBus().send(dbusMessage.createReply(true));
+                }
+            });
+            m_pendingWindows.push_back(toplevelWindow);
+            toplevelWindow->closeWindow();
+        }
+    }
+    m_closeTimer.start(std::chrono::seconds(10));
+    m_closeTimer.setSingleShot(true);
+    connect(&m_closeTimer, &QTimer::timeout, m_closingWindowsGuard.get(), [this, dbusMessage] {
+#if KWIN_BUILD_NOTIFICATIONS
+        QStringList apps;
+        apps.reserve(m_pendingWindows.size());
+        std::transform(m_pendingWindows.cbegin(), m_pendingWindows.cend(), std::back_inserter(apps), [](const XdgToplevelWindow *window) -> QString {
+            const auto service = KService::serviceByDesktopName(window->desktopFileName());
+            return QChar(u'•') + (service ? service->name() : window->caption());
+        });
+        apps.removeDuplicates();
+        qCDebug(KWIN_CORE) << "Not closed windows" << apps;
+        auto notification = new KNotification("cancellogout", KNotification::DefaultEvent | KNotification::Persistent);
+        notification->setText(i18n("The following applications did not close:\n%1", apps.join('\n')));
+        auto cancel = notification->addAction(i18nc("@action:button", "Cancel Logout"));
+        auto quit = notification->addAction(i18nc("@action::button", "Log Out Anyway"));
+        connect(cancel, &KNotificationAction::activated, m_closingWindowsGuard.get(), [dbusMessage, this] {
+            m_closingWindowsGuard.reset();
+            QDBusConnection::sessionBus().send(dbusMessage.createReply(false));
+        });
+        connect(quit, &KNotificationAction::activated, m_closingWindowsGuard.get(), [dbusMessage, this] {
+            m_closingWindowsGuard.reset();
+            QDBusConnection::sessionBus().send(dbusMessage.createReply(true));
+        });
+        connect(notification, &KNotification::closed, m_closingWindowsGuard.get(), [dbusMessage, this] {
+            m_closingWindowsGuard.reset();
+            QDBusConnection::sessionBus().send(dbusMessage.createReply(false));
+        });
+        notification->sendEvent();
+#else
+        m_closingWindowsGuard.reset();
+        QDBusConnection::sessionBus().send(dbusMessage.createReply(false));
+#endif
+    });
+    return true;
+}
+
 void SessionManager::quit()
 {
     qApp->quit();

src/sm.h

@@ -10,9 +10,11 @@
 
 #pragma once
 
+#include <QDBusContext>
 #include <QDataStream>
 #include <QRect>
 #include <QStringList>
+#include <QTimer>
 
 #include <KConfigGroup>
 
@@ -24,8 +26,9 @@ namespace KWin
 
 class X11Window;
 struct SessionInfo;
+class XdgToplevelWindow;
 
-class SessionManager : public QObject
+class SessionManager : public QObject, public QDBusContext
 {
     Q_OBJECT
 public:
@@ -57,6 +60,7 @@ public Q_SLOTS: // DBus API
     void loadSession(const QString &name);
     void aboutToSaveSession(const QString &name);
     void finishSaveSession(const QString &name);
+    bool closeWaylandWindows();
     void quit();
 
 private:
@@ -73,6 +77,9 @@ private:
     int m_sessionDesktop;
 
     QList<SessionInfo *> session;
+    QList<XdgToplevelWindow *> m_pendingWindows;
+    QTimer m_closeTimer;
+    std::unique_ptr<QObject> m_closingWindowsGuard;
 };
 
 struct SessionInfo