inputmethod: Allow forcing the display of the input method

This makes it possible to show the input method when using a client that
doesn't support Wayland input methods (e.g. Xwayland).

This adds 2 dbus API entry points:
- activeClientSupported property: That tells us if the current client
doesn't support text-input-v*
- forceActivate method: forces the activation of the input method. This
configures the input method in a state that we can use to forward the
input method's keystrokes to the client, emulating a hardware keyboard.

BUG: 4399911

src/inputmethod.cpp

@@ -236,11 +236,21 @@ void InputMethod::setTrackedWindow(Window *trackedWindow)
 
 void InputMethod::handleFocusedSurfaceChanged()
 {
-    SurfaceInterface *focusedSurface = waylandServer()->seat()->focusedTextInputSurface();
+    auto seat = waylandServer()->seat();
+    SurfaceInterface *focusedSurface = seat->focusedTextInputSurface();
+
     setTrackedWindow(waylandServer()->findWindow(focusedSurface));
     if (!focusedSurface) {
         setActive(false);
     }
+
+    const auto client = focusedSurface ? focusedSurface->client() : nullptr;
+    bool ret = seat->textInputV2()->clientSupportsTextInput(client)
+            || seat->textInputV3()->clientSupportsTextInput(client);
+    if (ret != m_activeClientSupportsTextInput) {
+        m_activeClientSupportsTextInput = ret;
+        Q_EMIT activeClientSupportsTextInputChanged();
+    }
 }
 
 void InputMethod::surroundingTextChanged()
@@ -809,4 +819,15 @@ void InputMethod::resetPendingPreedit()
     preedit.highlightRanges.clear();
 }
 
+bool InputMethod::activeClientSupportsTextInput() const
+{
+    return m_activeClientSupportsTextInput;
+}
+
+void InputMethod::forceActivate()
+{
+    setActive(true);
+    show();
+}
+
 }

src/inputmethod.h

@@ -72,6 +72,8 @@ public:
     bool shouldShowOnActive() const;
 
     void forwardModifiers(ForwardModifiersForce force);
+    bool activeClientSupportsTextInput() const;
+    void forceActivate();
 
 Q_SIGNALS:
     void panelChanged();
@@ -79,6 +81,7 @@ Q_SIGNALS:
     void enabledChanged(bool enabled);
     void visibleChanged();
     void availableChanged();
+    void activeClientSupportsTextInputChanged();
 
 private Q_SLOTS:
     // textinput interface slots
@@ -134,6 +137,7 @@ private:
     QString m_inputMethodCommand;
 
     bool m_hasPendingModifiers = false;
+    bool m_activeClientSupportsTextInput = false;
 };
 
 }

src/virtualkeyboard_dbus.cpp

@@ -23,6 +23,7 @@ VirtualKeyboardDBus::VirtualKeyboardDBus(InputMethod *parent)
     connect(parent, &InputMethod::enabledChanged, this, &VirtualKeyboardDBus::enabledChanged);
     connect(parent, &InputMethod::visibleChanged, this, &VirtualKeyboardDBus::visibleChanged);
     connect(parent, &InputMethod::availableChanged, this, &VirtualKeyboardDBus::availableChanged);
+    connect(parent, &InputMethod::activeClientSupportsTextInputChanged, this, &VirtualKeyboardDBus::activeClientSupportsTextInputChanged);
 }
 
 VirtualKeyboardDBus::~VirtualKeyboardDBus() = default;
@@ -57,9 +58,18 @@ bool VirtualKeyboardDBus::isAvailable() const
     return m_inputMethod->isAvailable();
 }
 
+bool VirtualKeyboardDBus::activeClientSupportsTextInput() const
+{
+    return m_inputMethod->activeClientSupportsTextInput();
+}
+
 bool VirtualKeyboardDBus::willShowOnActive() const
 {
     return isAvailable() && isEnabled() && m_inputMethod->shouldShowOnActive();
 }
 
+void VirtualKeyboardDBus::forceActivate()
+{
+    m_inputMethod->forceActivate();
+}
 }

src/virtualkeyboard_dbus.h

@@ -22,11 +22,13 @@ class KWIN_EXPORT VirtualKeyboardDBus : public QObject
     Q_PROPERTY(bool enabled READ isEnabled WRITE setEnabled NOTIFY enabledChanged)
     Q_PROPERTY(bool active READ isActive WRITE setActive NOTIFY activeChanged)
     Q_PROPERTY(bool visible READ isVisible NOTIFY visibleChanged)
+    Q_PROPERTY(bool activeClientSupportsTextInput READ activeClientSupportsTextInput NOTIFY activeClientSupportsTextInputChanged)
 public:
     explicit VirtualKeyboardDBus(InputMethod *inputMethod);
     ~VirtualKeyboardDBus() override;
     bool isEnabled() const;
 
+    bool activeClientSupportsTextInput() const;
     bool isVisible() const;
     bool isActive() const;
     bool isAvailable() const;
@@ -34,12 +36,14 @@ public:
     void setActive(bool active);
 
     Q_SCRIPTABLE bool willShowOnActive() const;
+    Q_SCRIPTABLE void forceActivate();
 
 Q_SIGNALS:
     Q_SCRIPTABLE void enabledChanged();
     Q_SCRIPTABLE void activeChanged();
     Q_SCRIPTABLE void visibleChanged();
     Q_SCRIPTABLE void availableChanged();
+    Q_SCRIPTABLE void activeClientSupportsTextInputChanged();
 
 private:
     InputMethod *const m_inputMethod;

src/wayland/textinput_v2_interface.cpp

@@ -561,4 +561,8 @@ bool TextInputV2Interface::isEnabled() const
     return d->surface && d->m_enabledSurfaces.contains(d->surface);
 }
 
+bool TextInputV2Interface::clientSupportsTextInput(ClientConnection *client) const
+{
+    return client && d->resourceMap().contains(*client);
+}
 }

src/wayland/textinput_v2_interface.h

@@ -13,6 +13,7 @@
 struct wl_resource;
 namespace KWaylandServer
 {
+class ClientConnection;
 class Display;
 class SeatInterface;
 class SurfaceInterface;
@@ -122,6 +123,11 @@ public:
      */
     QPointer<SurfaceInterface> surface() const;
 
+    /**
+     * @return whether @p client supports text-input-v2
+     */
+    bool clientSupportsTextInput(ClientConnection *client) const;
+
     /**
      * @return Whether the TextInputV2Interface is currently enabled for a SurfaceInterface.
      * @see surface

src/wayland/textinput_v3_interface.cpp

@@ -496,4 +496,8 @@ bool TextInputV3Interface::isEnabled() const
     return d->isEnabled();
 }
 
+bool TextInputV3Interface::clientSupportsTextInput(ClientConnection *client) const
+{
+    return client && d->resourceMap().contains(*client);
+}
 }

src/wayland/textinput_v3_interface.h

@@ -13,6 +13,7 @@
 struct wl_resource;
 namespace KWaylandServer
 {
+class ClientConnection;
 class Display;
 class SeatInterface;
 class SurfaceInterface;
@@ -148,6 +149,11 @@ public:
      */
     void done();
 
+    /**
+     * @return whether @p client supports text-input-v3
+     */
+    bool clientSupportsTextInput(ClientConnection *client) const;
+
 Q_SIGNALS:
 
     /**