LibWeb: Add Function To Build Accessiblity Tree

With this patch, the accessibility tree can be build from the root
node of a document. This can then be serialzed and sent to (soon
to come) consumers.

Userland/Libraries/LibWeb/CMakeLists.txt

@@ -72,6 +72,7 @@ set(SOURCES
     DOM/AbortController.cpp
     DOM/AbortSignal.cpp
     DOM/AbstractRange.cpp
+    DOM/AccessibilityTreeNode.cpp
     DOM/Attr.cpp
     DOM/Attr.idl
     DOM/ARIAMixin.cpp

Userland/Libraries/LibWeb/DOM/AccessibilityTreeNode.cpp

@@ -0,0 +1,76 @@
+/*
+ * Copyright (c) 2022, Jonah Shafran <jonahshafran@gmail.com>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <AK/Tuple.h>
+#include <LibWeb/DOM/AccessibilityTreeNode.h>
+#include <LibWeb/DOM/Document.h>
+#include <LibWeb/DOM/Element.h>
+#include <LibWeb/DOM/Node.h>
+#include <LibWeb/DOM/Text.h>
+
+namespace Web::DOM {
+
+JS::NonnullGCPtr<AccessibilityTreeNode> AccessibilityTreeNode::create(Document* document, DOM::Node const* value)
+{
+    return *document->heap().allocate<AccessibilityTreeNode>(document->realm(), value);
+}
+
+AccessibilityTreeNode::AccessibilityTreeNode(JS::GCPtr<DOM::Node> value)
+    : m_value(value)
+{
+    m_children = {};
+}
+
+void AccessibilityTreeNode::serialize_tree_as_json(JsonObjectSerializer<StringBuilder>& object) const
+{
+    if (value()->is_document()) {
+        VERIFY_NOT_REACHED();
+    } else if (value()->is_element()) {
+        auto const* element = static_cast<DOM::Element*>(value().ptr());
+
+        if (element->include_in_accessibility_tree()) {
+            MUST(object.add("type"sv, "element"sv));
+
+            auto role = element->role_or_default();
+            bool has_role = !role.is_null() && !role.is_empty() && !ARIARoleNames::is_abstract_aria_role(role);
+
+            if (has_role)
+                MUST(object.add("role"sv, role.view()));
+            else
+                MUST(object.add("role"sv, ""sv));
+        } else {
+            VERIFY_NOT_REACHED();
+        }
+
+    } else if (value()->is_text()) {
+        MUST(object.add("type"sv, "text"sv));
+
+        auto const* text_node = static_cast<DOM::Text*>(value().ptr());
+        MUST(object.add("text"sv, text_node->data()));
+    }
+
+    if (value()->has_child_nodes()) {
+        auto node_children = MUST(object.add_array("children"sv));
+        for (auto child : children()) {
+            if (child->value()->is_uninteresting_whitespace_node())
+                continue;
+            JsonObjectSerializer<StringBuilder> child_object = MUST(node_children.add_object());
+            child->serialize_tree_as_json(child_object);
+            MUST(child_object.finish());
+        }
+        MUST(node_children.finish());
+    }
+}
+
+void AccessibilityTreeNode::visit_edges(Visitor& visitor)
+{
+    Base::visit_edges(visitor);
+    visitor.visit(*value());
+    for (auto child : children())
+        child->visit_edges(visitor);
+}
+
+}

Userland/Libraries/LibWeb/DOM/AccessibilityTreeNode.h

@@ -0,0 +1,40 @@
+/*
+ * Copyright (c) 2022, Jonah Shafran <jonahshafran@gmail.com>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/JsonObjectSerializer.h>
+#include <AK/Vector.h>
+#include <LibJS/Heap/Cell.h>
+#include <LibWeb/DOM/Node.h>
+#include <LibWeb/Forward.h>
+
+namespace Web::DOM {
+
+class AccessibilityTreeNode final : public JS::Cell {
+    JS_CELL(AccessibilityTreeNode, JS::Cell)
+public:
+    static JS::NonnullGCPtr<AccessibilityTreeNode> create(Document*, DOM::Node const*);
+    virtual ~AccessibilityTreeNode() override = default;
+
+    JS::GCPtr<DOM::Node> value() const { return m_value; }
+    void set_value(JS::GCPtr<DOM::Node> value) { m_value = value; }
+    Vector<AccessibilityTreeNode*> children() const { return m_children; }
+    void append_child(AccessibilityTreeNode* child) { m_children.append(child); }
+
+    void serialize_tree_as_json(JsonObjectSerializer<StringBuilder>& object) const;
+
+protected:
+    virtual void visit_edges(Visitor&) override;
+
+private:
+    explicit AccessibilityTreeNode(JS::GCPtr<DOM::Node>);
+
+    JS::GCPtr<DOM::Node> m_value;
+    Vector<AccessibilityTreeNode*> m_children;
+};
+
+}

Userland/Libraries/LibWeb/Forward.h

@@ -136,6 +136,7 @@ namespace Web::DOM {
 class AbstractRange;
 class AbortController;
 class AbortSignal;
+class AccessibilityTreeNode;
 class Attr;
 class CDATASection;
 class CharacterData;