[GTK] Implement GTK4 accessibility

https://bugs.webkit.org/show_bug.cgi?id=227528

Reviewed by Carlos Garcia Campos.

WebKit maintains a complete AT-SPI accessible tree within the web
process, under a separate D-Bus name. This conflicts with GTK4's
expectations of having instances of GtkAccessible objects in process
that can be built in an internal tree.

GTK4 recently introduced support for bridging out-of-process AT-SPI
accessible trees using a new GtkAtSpiSocket object that implements
GtkAccessible [1]. The availability of this object is guarded by the
GTK_ACCESSIBILITY_ATSPI ifdef.

Use this new socket object from GTK to bridge the web page accessible
tree, and the UI process' one. Mark the textview widget as hidden from
the accessible tree.

Create the GtkAtSpiSocket accessible when the web page reports to be
ready. Inject the socket accessible as the first GtkAccessible child
of WebKitWebViewBase.

[1] https://gitlab.gnome.org/GNOME/gtk/-/merge_requests/6827

* Source/WebKit/UIProcess/API/gtk/WebKitWebViewBase.cpp:
(webkitWebViewBaseAccessibleGetFirstAccessibleChild):
(webkitWebViewBaseAccessibleInterfaceInit):
(webkitWebViewBaseSetPlugID):
* Source/WebKit/UIProcess/API/gtk/WebKitWebViewBasePrivate.h:
* Source/WebKit/UIProcess/gtk/KeyBindingTranslator.cpp:
(WebKit::KeyBindingTranslator::KeyBindingTranslator):
* Source/WebKit/UIProcess/gtk/WebPageProxyGtk.cpp:
(WebKit::WebPageProxy::bindAccessibilityTree):
* Source/WebKit/WebProcess/WebPage/glib/WebPageGLib.cpp:
(WebKit::WebPage::platformInitialize):

Canonical link: https://commits.webkit.org/274201@main

Source/WebKit/UIProcess/API/gtk/WebKitWebViewBase.cpp

@@ -97,6 +97,10 @@
 #include "WebFullScreenManagerProxy.h"
 #endif
 
+#if USE(GTK4) && defined(GTK_ACCESSIBILITY_ATSPI)
+#include <gtk/a11y/gtkatspi.h>
+#endif
+
 using namespace WebKit;
 using namespace WebCore;
 
@@ -300,7 +304,11 @@ struct _WebKitWebViewBasePrivate {
     CString tooltipText;
     IntRect tooltipArea;
     WebHitTestResultData::IsScrollbar mouseIsOverScrollbar;
-#if !USE(GTK4)
+#if USE(GTK4)
+#ifdef GTK_ACCESSIBILITY_ATSPI
+    GRefPtr<GtkAccessible> socketAccessible;
+#endif
+#else
     GRefPtr<AtkObject> accessible;
 #endif
     GtkWidget* dialog { nullptr };
@@ -376,7 +384,10 @@ struct _WebKitWebViewBasePrivate {
  */
 
 #if USE(GTK4)
-WEBKIT_DEFINE_TYPE(WebKitWebViewBase, webkit_web_view_base, GTK_TYPE_WIDGET)
+static void webkitWebViewBaseAccessibleInterfaceInit(GtkAccessibleInterface*);
+
+WEBKIT_DEFINE_TYPE_WITH_CODE(WebKitWebViewBase, webkit_web_view_base, GTK_TYPE_WIDGET,
+    G_IMPLEMENT_INTERFACE(GTK_TYPE_ACCESSIBLE, webkitWebViewBaseAccessibleInterfaceInit))
 #else
 WEBKIT_DEFINE_TYPE(WebKitWebViewBase, webkit_web_view_base, GTK_TYPE_CONTAINER)
 #endif
@@ -387,6 +398,29 @@ static void webkitWebViewBaseDidExitFullScreen(WebKitWebViewBase*);
 static void webkitWebViewBaseRequestExitFullScreen(WebKitWebViewBase*);
 #endif
 
+#if USE(GTK4)
+static GtkAccessible* webkitWebViewBaseAccessibleGetFirstAccessibleChild(GtkAccessible* accessible)
+{
+    WebKitWebViewBase* webView = WEBKIT_WEB_VIEW_BASE(accessible);
+
+#ifdef GTK_ACCESSIBILITY_ATSPI
+    if (webView->priv->socketAccessible)
+        return GTK_ACCESSIBLE(g_object_ref(webView->priv->socketAccessible.get()));
+#endif
+
+    if (auto* widget = gtk_widget_get_first_child(GTK_WIDGET(webView)))
+        return GTK_ACCESSIBLE(g_object_ref(widget));
+
+    return nullptr;
+}
+
+static void
+webkitWebViewBaseAccessibleInterfaceInit(GtkAccessibleInterface* iface)
+{
+    iface->get_first_accessible_child = webkitWebViewBaseAccessibleGetFirstAccessibleChild;
+}
+#endif
+
 static void webkitWebViewBaseUpdateDisplayID(WebKitWebViewBase* webViewBase, GdkMonitor* monitor)
 {
     if (!monitor)
@@ -3440,3 +3474,34 @@ void webkitWebViewBaseCallAfterNextPresentationUpdate(WebKitWebViewBase* webView
 {
     webkitWebViewBaseNextPresentationUpdateMonitorStart(webViewBase, WTFMove(callback));
 }
+
+#if USE(GTK4)
+void webkitWebViewBaseSetPlugID(WebKitWebViewBase* webViewBase, const String& plugID)
+{
+#ifdef GTK_ACCESSIBILITY_ATSPI
+    WebKitWebViewBasePrivate* priv = webViewBase->priv;
+
+    if (priv->socketAccessible) {
+        gtk_accessible_set_accessible_parent(priv->socketAccessible.get(), nullptr, nullptr);
+        priv->socketAccessible = nullptr;
+    }
+
+    Vector<String> tokens = plugID.split(':');
+    RELEASE_ASSERT(tokens.size() == 2);
+
+    GUniqueOutPtr<GError> error;
+    GUniquePtr<char> busName(g_strdup_printf(":%s", tokens[0].utf8().data()));
+
+    priv->socketAccessible = adoptGRef(gtk_at_spi_socket_new(busName.get(), tokens[1].utf8().data(), &error.outPtr()));
+
+    if (priv->socketAccessible) {
+        auto* widget = gtk_widget_get_first_child(GTK_WIDGET(webViewBase));
+        gtk_accessible_set_accessible_parent(priv->socketAccessible.get(), GTK_ACCESSIBLE(webViewBase), GTK_ACCESSIBLE(widget));
+    } else
+        g_warning("Error creating WebKitWebView a11y socket: %s", error->message);
+#else
+    UNUSED_PARAM(webViewBase);
+    UNUSED_PARAM(plugID);
+#endif // GTK_ACCESSIBILITY_ATSPI
+}
+#endif

Source/WebKit/UIProcess/API/gtk/WebKitWebViewBasePrivate.h

@@ -141,3 +141,7 @@ void webkitWebViewBaseToplevelWindowStateChanged(WebKitWebViewBase*, uint32_t, u
 void webkitWebViewBaseToplevelWindowMonitorChanged(WebKitWebViewBase*, GdkMonitor*);
 
 void webkitWebViewBaseCallAfterNextPresentationUpdate(WebKitWebViewBase*, CompletionHandler<void()>&&);
+
+#if USE(GTK4)
+void webkitWebViewBaseSetPlugID(WebKitWebViewBase*, const String&);
+#endif

Source/WebKit/UIProcess/gtk/KeyBindingTranslator.cpp

@@ -173,6 +173,9 @@ static void moveCursorCallback(GtkWidget* widget, GtkMovementStep step, gint cou
 KeyBindingTranslator::KeyBindingTranslator()
     : m_nativeWidget(gtk_text_view_new())
 {
+#if USE(GTK4)
+    gtk_accessible_update_state(GTK_ACCESSIBLE(m_nativeWidget.get()), GTK_ACCESSIBLE_STATE_HIDDEN, TRUE, -1);
+#endif
     g_signal_connect(m_nativeWidget.get(), "backspace", G_CALLBACK(backspaceCallback), this);
     g_signal_connect(m_nativeWidget.get(), "cut-clipboard", G_CALLBACK(cutClipboardCallback), this);
     g_signal_connect(m_nativeWidget.get(), "copy-clipboard", G_CALLBACK(copyClipboardCallback), this);

Source/WebKit/UIProcess/gtk/WebPageProxyGtk.cpp

@@ -54,8 +54,7 @@ GtkWidget* WebPageProxy::viewWidget()
 void WebPageProxy::bindAccessibilityTree(const String& plugID)
 {
 #if USE(GTK4)
-    // FIXME: We need a way to override accessible interface of WebView and send the atspi reference to the web process.
-    ASSERT_NOT_IMPLEMENTED_YET();
+    webkitWebViewBaseSetPlugID(WEBKIT_WEB_VIEW_BASE(viewWidget()), plugID);
 #else
     auto* accessible = gtk_widget_get_accessible(viewWidget());
     atk_socket_embed(ATK_SOCKET(accessible), const_cast<char*>(plugID.utf8().data()));

Source/WebKit/WebProcess/WebPage/glib/WebPageGLib.cpp

@@ -61,9 +61,6 @@ void WebPage::platformInitialize(const WebPageCreationParameters&)
     // entry point to the Web process, and send a message to the UI
     // process to connect the two worlds through the accessibility
     // object there specifically placed for that purpose (the socket).
-#if PLATFORM(GTK) && USE(GTK4)
-    // FIXME: we need a way to connect DOM and app a11y tree in GTK4.
-#else
     if (auto* page = corePage()) {
         m_accessibilityRootObject = AccessibilityRootAtspi::create(*page);
         m_accessibilityRootObject->registerObject([&](const String& plugID) {
@@ -72,7 +69,6 @@ void WebPage::platformInitialize(const WebPageCreationParameters&)
         });
     }
 #endif
-#endif
 }
 
 void WebPage::platformDetach()