LibWeb: Implement ParentNode.prepend

`convert_nodes_to_single_node` is inside its own file so ChildNode can
include and use it without having to include other headers such as
DOM/Node.h. This is to prevent circular includes.

Userland/Libraries/LibWeb/CMakeLists.txt

@@ -80,6 +80,7 @@ set(SOURCES
     DOM/LiveNodeList.cpp
     DOM/NamedNodeMap.cpp
     DOM/Node.cpp
+    DOM/NodeOperations.cpp
     DOM/ParentNode.cpp
     DOM/Position.cpp
     DOM/ProcessingInstruction.cpp

Userland/Libraries/LibWeb/DOM/ChildNode.h

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2021, Luke Wilde <lukew@serenityos.org>
+ * Copyright (c) 2021-2022, Luke Wilde <lukew@serenityos.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */

Userland/Libraries/LibWeb/DOM/Document.idl

@@ -65,6 +65,8 @@ interface Document : Node {
     readonly attribute Element? lastElementChild;
     readonly attribute unsigned long childElementCount;
 
+    [CEReactions, Unscopable] undefined prepend((Node or DOMString)... nodes);
+
     Element? querySelector(DOMString selectors);
     [NewObject] NodeList querySelectorAll(DOMString selectors);
 

Userland/Libraries/LibWeb/DOM/DocumentFragment.idl

@@ -9,6 +9,8 @@ interface DocumentFragment : Node {
     readonly attribute Element? lastElementChild;
     readonly attribute unsigned long childElementCount;
 
+    [CEReactions, Unscopable] undefined prepend((Node or DOMString)... nodes);
+
     Element? querySelector(DOMString selectors);
     [NewObject] NodeList querySelectorAll(DOMString selectors);
 

Userland/Libraries/LibWeb/DOM/Element.idl

@@ -33,11 +33,13 @@ interface Element : Node {
 
     [ImplementedAs=style_for_bindings] readonly attribute CSSStyleDeclaration style;
 
-    // FIXME: These should all come from a ParentNode mixin
+    // FIXME: These should all come from a ParentNode mixin (up to and including children)
     readonly attribute Element? firstElementChild;
     readonly attribute Element? lastElementChild;
     readonly attribute unsigned long childElementCount;
 
+    [CEReactions, Unscopable] undefined prepend((Node or DOMString)... nodes);
+
     Element? querySelector(DOMString selectors);
     [NewObject] NodeList querySelectorAll(DOMString selectors);
 

Userland/Libraries/LibWeb/DOM/NodeOperations.cpp

@@ -0,0 +1,46 @@
+/*
+ * Copyright (c) 2022, Luke Wilde <lukew@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <AK/String.h>
+#include <AK/Vector.h>
+#include <LibWeb/DOM/DocumentFragment.h>
+#include <LibWeb/DOM/NodeOperations.h>
+#include <LibWeb/DOM/Text.h>
+
+namespace Web::DOM {
+
+// https://dom.spec.whatwg.org/#converting-nodes-into-a-node
+ExceptionOr<NonnullRefPtr<Node>> convert_nodes_to_single_node(Vector<Variant<NonnullRefPtr<Node>, String>> const& nodes, DOM::Document& document)
+{
+    // 1. Let node be null.
+    // 2. Replace each string in nodes with a new Text node whose data is the string and node document is document.
+    // 3. If nodes contains one node, then set node to nodes[0].
+    // 4. Otherwise, set node to a new DocumentFragment node whose node document is document, and then append each node in nodes, if any, to it.
+    // 5. Return node.
+
+    auto potentially_convert_string_to_text_node = [&document](Variant<NonnullRefPtr<Node>, String> const& node) -> NonnullRefPtr<Node> {
+        if (node.has<NonnullRefPtr<Node>>())
+            return node.get<NonnullRefPtr<Node>>();
+
+        return adopt_ref(*new Text(document, node.get<String>()));
+    };
+
+    if (nodes.size() == 1)
+        return potentially_convert_string_to_text_node(nodes.first());
+
+    // This is NNRP<Node> instead of NNRP<DocumentFragment> to be compatible with the return type.
+    NonnullRefPtr<Node> document_fragment = adopt_ref(*new DocumentFragment(document));
+    for (auto& unconverted_node : nodes) {
+        auto node = potentially_convert_string_to_text_node(unconverted_node);
+        auto result = document_fragment->append_child(node);
+        if (result.is_exception())
+            return result.exception();
+    }
+
+    return document_fragment;
+}
+
+}

Userland/Libraries/LibWeb/DOM/NodeOperations.h

@@ -0,0 +1,16 @@
+/*
+ * Copyright (c) 2022, Luke Wilde <lukew@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/NonnullRefPtr.h>
+#include <LibWeb/Forward.h>
+
+namespace Web::DOM {
+
+ExceptionOr<NonnullRefPtr<Node>> convert_nodes_to_single_node(Vector<Variant<NonnullRefPtr<Node>, String>> const& nodes, DOM::Document& document);
+
+}

Userland/Libraries/LibWeb/DOM/ParentNode.cpp

@@ -7,6 +7,7 @@
 #include <LibWeb/CSS/Parser/Parser.h>
 #include <LibWeb/CSS/SelectorEngine.h>
 #include <LibWeb/DOM/HTMLCollection.h>
+#include <LibWeb/DOM/NodeOperations.h>
 #include <LibWeb/DOM/ParentNode.h>
 #include <LibWeb/DOM/StaticNodeList.h>
 #include <LibWeb/Dump.h>
@@ -155,4 +156,22 @@ NonnullRefPtr<HTMLCollection> ParentNode::get_elements_by_tag_name_ns(FlyString
     });
 }
 
+// https://dom.spec.whatwg.org/#dom-parentnode-prepend
+ExceptionOr<void> ParentNode::prepend(Vector<Variant<NonnullRefPtr<Node>, String>> const& nodes)
+{
+    // 1. Let node be the result of converting nodes into a node given nodes and this’s node document.
+    auto node_or_exception = convert_nodes_to_single_node(nodes, document());
+    if (node_or_exception.is_exception())
+        return node_or_exception.exception();
+
+    auto node = node_or_exception.release_value();
+
+    // 2. Pre-insert node into this before this’s first child.
+    auto result = pre_insert(node, first_child());
+    if (result.is_exception())
+        return result.exception();
+
+    return {};
+}
+
 }

Userland/Libraries/LibWeb/DOM/ParentNode.h

@@ -30,6 +30,8 @@ public:
     NonnullRefPtr<HTMLCollection> get_elements_by_tag_name(FlyString const&);
     NonnullRefPtr<HTMLCollection> get_elements_by_tag_name_ns(FlyString const&, FlyString const&);
 
+    ExceptionOr<void> prepend(Vector<Variant<NonnullRefPtr<Node>, String>> const& nodes);
+
 protected:
     ParentNode(Document& document, NodeType type)
         : Node(document, type)