LibWeb: Add support for DOM's TreeWalker

This patch adds TreeWalker (created via Document.createTreeWalker())
which allows you to traverse a filtered view of the DOM in all
directions.

Userland/Libraries/LibWeb/DOM/TreeWalker.cpp

@@ -0,0 +1,375 @@
+/*
+ * Copyright (c) 2022, Andreas Kling <kling@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibWeb/Bindings/DOMExceptionWrapper.h>
+#include <LibWeb/Bindings/IDLAbstractOperations.h>
+#include <LibWeb/Bindings/NodeWrapper.h>
+#include <LibWeb/Bindings/NodeWrapperFactory.h>
+#include <LibWeb/Bindings/Wrapper.h>
+#include <LibWeb/DOM/DOMException.h>
+#include <LibWeb/DOM/Node.h>
+#include <LibWeb/DOM/NodeFilter.h>
+#include <LibWeb/DOM/TreeWalker.h>
+
+namespace Web::DOM {
+
+TreeWalker::TreeWalker(Node& root)
+    : m_root(root)
+    , m_current(root)
+{
+}
+
+TreeWalker::~TreeWalker()
+{
+}
+
+// https://dom.spec.whatwg.org/#dom-document-createtreewalker
+NonnullRefPtr<TreeWalker> TreeWalker::create(Node& root, unsigned what_to_show, RefPtr<NodeFilter> filter)
+{
+    // 1. Let walker be a new TreeWalker object.
+    // 2. Set walker’s root and walker’s current to root.
+    auto walker = adopt_ref(*new TreeWalker(root));
+
+    // 3. Set walker’s whatToShow to whatToShow.
+    walker->m_what_to_show = what_to_show;
+
+    // 4. Set walker’s filter to filter.
+    walker->m_filter = move(filter);
+
+    // 5. Return walker.
+    return walker;
+}
+
+// https://dom.spec.whatwg.org/#dom-treewalker-currentnode
+NonnullRefPtr<Node> TreeWalker::current_node() const
+{
+    return *m_current;
+}
+
+// https://dom.spec.whatwg.org/#dom-treewalker-currentnode
+void TreeWalker::set_current_node(Node& node)
+{
+    m_current = node;
+}
+
+// https://dom.spec.whatwg.org/#dom-treewalker-parentnode
+JS::ThrowCompletionOr<RefPtr<Node>> TreeWalker::parent_node()
+{
+    // 1. Let node be this’s current.
+    RefPtr<Node> node = m_current;
+
+    // 2. While node is non-null and is not this’s root:
+    while (node && node != m_root) {
+        // 1. Set node to node’s parent.
+        node = node->parent();
+
+        // 2. If node is non-null and filtering node within this returns FILTER_ACCEPT,
+        //    then set this’s current to node and return node.
+        if (node) {
+            auto result = filter(*node);
+            if (result.is_throw_completion())
+                return result.release_error();
+            if (result.value() == NodeFilter::FILTER_ACCEPT) {
+                m_current = *node;
+                return node;
+            }
+        }
+    }
+
+    return RefPtr<Node> {};
+}
+
+// https://dom.spec.whatwg.org/#dom-treewalker-firstchild
+JS::ThrowCompletionOr<RefPtr<Node>> TreeWalker::first_child()
+{
+    return traverse_children(ChildTraversalType::First);
+}
+
+// https://dom.spec.whatwg.org/#dom-treewalker-lastchild
+JS::ThrowCompletionOr<RefPtr<Node>> TreeWalker::last_child()
+{
+    return traverse_children(ChildTraversalType::Last);
+}
+
+// https://dom.spec.whatwg.org/#dom-treewalker-previoussibling
+JS::ThrowCompletionOr<RefPtr<Node>> TreeWalker::previous_sibling()
+{
+    return traverse_siblings(SiblingTraversalType::Previous);
+}
+
+// https://dom.spec.whatwg.org/#dom-treewalker-nextsibling
+JS::ThrowCompletionOr<RefPtr<Node>> TreeWalker::next_sibling()
+{
+    return traverse_siblings(SiblingTraversalType::Next);
+}
+
+// https://dom.spec.whatwg.org/#dom-treewalker-previousnode
+JS::ThrowCompletionOr<RefPtr<Node>> TreeWalker::previous_node()
+{
+    // 1. Let node be this’s current.
+    RefPtr<Node> node = m_current;
+
+    // 2. While node is not this’s root:
+    while (node != m_root) {
+        // 1. Let sibling be node’s previous sibling.
+        RefPtr<Node> sibling = node->previous_sibling();
+
+        // 2. While sibling is non-null:
+        while (sibling) {
+            // 1. Set node to sibling.
+            node = sibling;
+
+            // 2. Let result be the result of filtering node within this.
+            auto result = TRY(filter(*node));
+
+            // 3. While result is not FILTER_REJECT and node has a child:
+            while (result != NodeFilter::FILTER_REJECT && node->has_children()) {
+                // 1. Set node to node’s last child.
+                node = node->last_child();
+
+                // 2. Set result to the result of filtering node within this.
+                result = TRY(filter(*node));
+            }
+
+            // 4. If result is FILTER_ACCEPT, then set this’s current to node and return node.
+            if (result == NodeFilter::FILTER_ACCEPT) {
+                m_current = *node;
+                return node;
+            }
+
+            // 5. Set sibling to node’s previous sibling.
+            sibling = node->previous_sibling();
+        }
+
+        // 3. If node is this’s root or node’s parent is null, then return null.
+        if (node == m_root || !node->parent())
+            return nullptr;
+
+        // 4. Set node to node’s parent.
+        node = node->parent();
+
+        // 5. If the return value of filtering node within this is FILTER_ACCEPT, then set this’s current to node and return node.
+        if (TRY(filter(*node)) == NodeFilter::FILTER_ACCEPT) {
+            m_current = *node;
+            return node;
+        }
+    }
+    // 3. Return null.
+    return nullptr;
+}
+
+// https://dom.spec.whatwg.org/#dom-treewalker-nextnode
+JS::ThrowCompletionOr<RefPtr<Node>> TreeWalker::next_node()
+{
+    // 1. Let node be this’s current.
+    RefPtr<Node> node = m_current;
+
+    // 2. Let result be FILTER_ACCEPT.
+    auto result = NodeFilter::FILTER_ACCEPT;
+
+    // 3. While true:
+    while (true) {
+        // 1. While result is not FILTER_REJECT and node has a child:
+        while (result != NodeFilter::FILTER_REJECT && node->has_children()) {
+            // 1. Set node to its first child.
+            node = node->first_child();
+
+            // 2. Set result to the result of filtering node within this.
+            auto result = TRY(filter(*node));
+
+            // 3. If result is FILTER_ACCEPT, then set this’s current to node and return node.
+            if (result == NodeFilter::FILTER_ACCEPT) {
+                m_current = *node;
+                return node;
+            }
+        }
+
+        // 2. Let sibling be null.
+        RefPtr<Node> sibling = nullptr;
+
+        // 3. Let temporary be node.
+        RefPtr<Node> temporary = node;
+
+        // 4. While temporary is non-null:
+        while (temporary) {
+            // 1. If temporary is this’s root, then return null.
+            if (temporary == m_root)
+                return nullptr;
+
+            // 2. Set sibling to temporary’s next sibling.
+            sibling = temporary->next_sibling();
+
+            // 3. If sibling is non-null, then set node to sibling and break.
+            if (sibling) {
+                node = sibling;
+                break;
+            }
+
+            // 4. Set temporary to temporary’s parent.
+            temporary = temporary->parent();
+        }
+
+        // 5. Set result to the result of filtering node within this.
+        result = TRY(filter(*node));
+
+        // 6. If result is FILTER_ACCEPT, then set this’s current to node and return node.
+        if (result == NodeFilter::FILTER_ACCEPT) {
+            m_current = *node;
+            return node;
+        }
+    }
+}
+
+// https://dom.spec.whatwg.org/#concept-node-filter
+JS::ThrowCompletionOr<NodeFilter::Result> TreeWalker::filter(Node& node)
+{
+    VERIFY(wrapper());
+    auto& global_object = wrapper()->global_object();
+
+    // 1. If traverser’s active flag is set, then throw an "InvalidStateError" DOMException.
+    if (m_active)
+        return JS::throw_completion(wrap(global_object, InvalidStateError::create("NodeIterator is already active")));
+
+    // 2. Let n be node’s nodeType attribute value − 1.
+    auto n = node.node_type() - 1;
+
+    // 3. If the nth bit (where 0 is the least significant bit) of traverser’s whatToShow is not set, then return FILTER_SKIP.
+    if (!(m_what_to_show & (1u << n)))
+        return NodeFilter::FILTER_SKIP;
+
+    // 4. If traverser’s filter is null, then return FILTER_ACCEPT.
+    if (!m_filter)
+        return NodeFilter::FILTER_ACCEPT;
+
+    // 5. Set traverser’s active flag.
+    m_active = true;
+
+    // 6. Let result be the return value of call a user object’s operation with traverser’s filter, "acceptNode", and « node ».
+    //    If this throws an exception, then unset traverser’s active flag and rethrow the exception.
+    auto result = Bindings::IDL::call_user_object_operation(m_filter->callback(), "acceptNode", {}, wrap(global_object, node));
+    if (result.is_abrupt()) {
+        m_active = false;
+        return result;
+    }
+
+    // 7. Unset traverser’s active flag.
+    m_active = false;
+
+    // 8. Return result.
+    auto result_value = TRY(result.value()->to_i32(global_object));
+    return static_cast<NodeFilter::Result>(result_value);
+}
+
+// https://dom.spec.whatwg.org/#concept-traverse-children
+JS::ThrowCompletionOr<RefPtr<Node>> TreeWalker::traverse_children(ChildTraversalType type)
+{
+    // 1. Let node be walker’s current.
+    RefPtr<Node> node = m_current;
+
+    // 2. Set node to node’s first child if type is first, and node’s last child if type is last.
+    node = type == ChildTraversalType::First ? node->first_child() : node->last_child();
+
+    // 3. While node is non-null:
+    while (node) {
+        // 1. Let result be the result of filtering node within walker.
+        auto result = TRY(filter(*node));
+
+        // 2. If result is FILTER_ACCEPT, then set walker’s current to node and return node.
+        if (result == NodeFilter::FILTER_ACCEPT) {
+            m_current = *node;
+            return node;
+        }
+
+        // 3. If result is FILTER_SKIP, then:
+        if (result == NodeFilter::FILTER_SKIP) {
+            // 1. Let child be node’s first child if type is first, and node’s last child if type is last.
+            RefPtr<Node> child = type == ChildTraversalType::First ? node->first_child() : node->last_child();
+
+            // 2. If child is non-null, then set node to child and continue.
+            if (child) {
+                node = child.release_nonnull();
+                continue;
+            }
+        }
+
+        // 4. While node is non-null:
+        while (node) {
+            // 1. Let sibling be node’s next sibling if type is first, and node’s previous sibling if type is last.
+            RefPtr<Node> sibling = type == ChildTraversalType::First ? node->next_sibling() : node->previous_sibling();
+
+            // 2. If sibling is non-null, then set node to sibling and break.
+            if (sibling) {
+                node = sibling.release_nonnull();
+                break;
+            }
+
+            // 3. Let parent be node’s parent.
+            RefPtr<Node> parent = node->parent();
+
+            // 4. If parent is null, walker’s root, or walker’s current, then return null.
+            if (!parent || parent == m_root || parent == m_current)
+                return nullptr;
+
+            // 5. Set node to parent.
+            node = parent.release_nonnull();
+        }
+    }
+
+    // 4. Return null.
+    return nullptr;
+}
+
+// https://dom.spec.whatwg.org/#concept-traverse-siblings
+JS::ThrowCompletionOr<RefPtr<Node>> TreeWalker::traverse_siblings(SiblingTraversalType type)
+{
+    // 1. Let node be walker’s current.
+    RefPtr<Node> node = m_current;
+
+    // 2. If node is root, then return null.
+    if (node == m_root)
+        return nullptr;
+
+    // 3. While true:
+    while (true) {
+        // 1. Let sibling be node’s next sibling if type is next, and node’s previous sibling if type is previous.
+        RefPtr<Node> sibling = type == SiblingTraversalType::Next ? node->next_sibling() : node->previous_sibling();
+
+        // 2. While sibling is non-null:
+        while (sibling) {
+            // 1. Set node to sibling.
+            node = sibling;
+
+            // 2. Let result be the result of filtering node within walker.
+            auto result = TRY(filter(*node));
+
+            // 3. If result is FILTER_ACCEPT, then set walker’s current to node and return node.
+            if (result == NodeFilter::FILTER_ACCEPT) {
+                m_current = *node;
+                return node;
+            }
+
+            // 4. Set sibling to node’s first child if type is next, and node’s last child if type is previous.
+            sibling = type == SiblingTraversalType::Next ? node->first_child() : node->last_child();
+
+            // 5. If result is FILTER_REJECT or sibling is null, then set sibling to node’s next sibling if type is next, and node’s previous sibling if type is previous.
+            if (result == NodeFilter::FILTER_REJECT || !sibling)
+                sibling = type == SiblingTraversalType::Next ? node->next_sibling() : node->previous_sibling();
+        }
+
+        // 3. Set node to node’s parent.
+        node = node->parent();
+
+        // 4. If node is null or walker’s root, then return null.
+        if (!node || node == m_root)
+            return nullptr;
+
+        // 5. If the return value of filtering node within walker is FILTER_ACCEPT, then return null.
+        if (TRY(filter(*node)) == NodeFilter::FILTER_ACCEPT)
+            return nullptr;
+    }
+}
+
+}