LibHTML: Add parse_html_fragment()

This function parses a partial DOM and returns it wrapped in a document
fragment node (DocumentFragment.)

There are now two entrances into the HTML parser, one for parsing full
documents, and one for parsing fragments. Internally the both wrap the
same parsing function.

Libraries/LibHTML/Parser/HTMLParser.cpp

@@ -2,6 +2,7 @@
 #include <AK/NonnullRefPtrVector.h>
 #include <AK/StringBuilder.h>
 #include <LibHTML/DOM/Comment.h>
+#include <LibHTML/DOM/DocumentFragment.h>
 #include <LibHTML/DOM/DocumentType.h>
 #include <LibHTML/DOM/Element.h>
 #include <LibHTML/DOM/ElementFactory.h>
@@ -33,13 +34,10 @@ static bool is_self_closing_tag(const StringView& tag_name)
         || tag_name == "wbr";
 }
 
-NonnullRefPtr<Document> parse_html(const StringView& html, const URL& url)
+static bool parse_html(const StringView& html, Document& document, ParentNode& root)
 {
     NonnullRefPtrVector<ParentNode> node_stack;
-
-    auto document = adopt(*new Document);
-    document->set_url(url);
-    node_stack.append(document);
+    node_stack.append(root);
 
     enum class State {
         Free = 0,
@@ -309,6 +307,27 @@ NonnullRefPtr<Document> parse_html(const StringView& html, const URL& url)
         }
     }
 
+    return true;
+}
+
+RefPtr<DocumentFragment> parse_html_fragment(Document& document, const StringView& html)
+{
+    auto fragment = adopt(*new DocumentFragment(document));
+    if (!parse_html(html, document, *fragment))
+        return nullptr;
+    return fragment;
+}
+
+NonnullRefPtr<Document> parse_html(const StringView& html, const URL& url)
+{
+    auto document = adopt(*new Document);
+    document->set_url(url);
+
+    bool success = parse_html(html, *document, *document);
+    ASSERT(success);
+
+    document->fixup();
+
     Function<void(Node&)> fire_insertion_callbacks = [&](Node& node) {
         for (auto* child = node.first_child(); child; child = child->next_sibling()) {
             fire_insertion_callbacks(*child);
@@ -316,8 +335,7 @@ NonnullRefPtr<Document> parse_html(const StringView& html, const URL& url)
         if (node.parent())
             node.inserted_into(*node.parent());
     };
+    fire_insertion_callbacks(document);
 
-    document->fixup();
-    fire_insertion_callbacks(*document);
     return document;
 }

Libraries/LibHTML/Parser/HTMLParser.h

@@ -3,5 +3,7 @@
 #include <AK/NonnullRefPtr.h>
 #include <LibHTML/DOM/Document.h>
 
-NonnullRefPtr<Document> parse_html(const StringView&, const URL& = URL());
+class DocumentFragment;
 
+NonnullRefPtr<Document> parse_html(const StringView&, const URL& = URL());
+RefPtr<DocumentFragment> parse_html_fragment(Document&, const StringView&);