LibWeb: Bring fragment parsing up to spec

Corresponds to whatwg/html#10874

Also, parse_fragment() returns ExceptionOr, so stop voiding the error
from append_child().

Libraries/LibWeb/DOM/Element.cpp

@@ -1545,18 +1545,17 @@ WebIDL::ExceptionOr<GC::Ref<DOM::DocumentFragment>> Element::parse_fragment(Stri
         dbgln("FIXME: Handle fragment parsing of XML documents");
     }
 
-    // 3. Let new children be the result of invoking algorithm given markup, with context set to context.
+    // 3. Let newChildren be the result of invoking algorithm given context and markup.
     auto new_children = algorithm(*this, markup, HTML::HTMLParser::AllowDeclarativeShadowRoots::No);
 
     // 4. Let fragment be a new DocumentFragment whose node document is context's node document.
     auto fragment = realm().create<DOM::DocumentFragment>(document());
 
-    // 5. Append each Node in new children to fragment (in tree order).
-    for (auto& child : new_children) {
-        // I don't know if this can throw here, but let's be safe.
-        (void)TRY(fragment->append_child(*child));
-    }
+    // 5. For each node of newChildren, in tree order: append node to fragment.
+    for (auto& child : new_children)
+        TRY(fragment->append_child(*child));
 
+    // 6. Return fragment.
     return fragment;
 }
 

Libraries/LibWeb/HTML/Parser/HTMLParser.cpp

@@ -4453,29 +4453,32 @@ DOM::Document& HTMLParser::document()
 // https://html.spec.whatwg.org/multipage/parsing.html#parsing-html-fragments
 Vector<GC::Root<DOM::Node>> HTMLParser::parse_html_fragment(DOM::Element& context_element, StringView markup, AllowDeclarativeShadowRoots allow_declarative_shadow_roots)
 {
-    // 1. Create a new Document node, and mark it as being an HTML document.
+    // 1. Let document be a Document node whose type is "html".
     auto temp_document = DOM::Document::create_for_fragment_parsing(context_element.realm());
     temp_document->set_document_type(DOM::Document::Type::HTML);
 
     // AD-HOC: We set the about base URL of the document to the same as the context element's document.
     //         This is required for Document::parse_url() to work inside iframe srcdoc documents.
     temp_document->set_about_base_url(context_element.document().about_base_url());
 
-    // 2. If the node document of the context element is in quirks mode, then let the Document be in quirks mode.
-    //    Otherwise, the node document of the context element is in limited-quirks mode, then let the Document be in limited-quirks mode.
-    //    Otherwise, leave the Document in no-quirks mode.
-    temp_document->set_quirks_mode(context_element.document().mode());
+    // 2. If context's node document is in quirks mode, then set document's mode to "quirks".
+    if (context_element.document().in_quirks_mode())
+        temp_document->set_quirks_mode(DOM::QuirksMode::Yes);
 
-    // 3. If allowDeclarativeShadowRoots is true, then set Document's allow declarative shadow roots to true.
+    // 3. Otherwise, if context's node document is in limited-quirks mode, then set document's mode to "limited-quirks".
+    else if (context_element.document().in_limited_quirks_mode())
+        temp_document->set_quirks_mode(DOM::QuirksMode::Limited);
+
+    // 4. If allowDeclarativeShadowRoots is true, then set document's allow declarative shadow roots to true.
     if (allow_declarative_shadow_roots == AllowDeclarativeShadowRoots::Yes)
         temp_document->set_allow_declarative_shadow_roots(true);
 
-    // 4. Create a new HTML parser, and associate it with the just created Document node.
+    // 5. Create a new HTML parser, and associate it with document.
     auto parser = HTMLParser::create(*temp_document, markup, "utf-8"sv);
     parser->m_context_element = context_element;
     parser->m_parsing_fragment = true;
 
-    // 5. Set the state of the HTML parser's tokenization stage as follows, switching on the context element:
+    // 6. Set the state of the HTML parser's tokenization stage as follows, switching on the context element:
     // - title
     // - textarea
     if (context_element.local_name().is_one_of(HTML::TagNames::title, HTML::TagNames::textarea)) {
@@ -4512,37 +4515,36 @@ Vector<GC::Root<DOM::Node>> HTMLParser::parse_html_fragment(DOM::Element& contex
         // Leave the tokenizer in the data state.
     }
 
-    // 6. Let root be a new html element with no attributes.
-    auto root = create_element(context_element.document(), HTML::TagNames::html, Namespace::HTML).release_value_but_fixme_should_propagate_errors();
+    // 7. Let root be the result of creating an element given document, "html", and the HTML namespace.
+    auto root = MUST(create_element(context_element.document(), HTML::TagNames::html, Namespace::HTML));
 
-    // 7. Append the element root to the Document node created above.
+    // 8. Append root to document.
     MUST(temp_document->append_child(root));
 
-    // 8. Set up the parser's stack of open elements so that it contains just the single element root.
+    // 9. Set up the HTML parser's stack of open elements so that it contains just the single element root.
     parser->m_stack_of_open_elements.push(root);
 
-    // 9. If the context element is a template element,
-    if (context_element.local_name() == HTML::TagNames::template_) {
-        // push "in template" onto the stack of template insertion modes so that it is the new current template insertion mode.
+    // 10. If context is a template element, then push "in template" onto the stack of template insertion modes
+    //     so that it is the new current template insertion mode.
+    if (context_element.local_name() == HTML::TagNames::template_)
         parser->m_stack_of_template_insertion_modes.append(InsertionMode::InTemplate);
-    }
 
-    // FIXME: 10. Create a start tag token whose name is the local name of context and whose attributes are the attributes of context.
-    //           Let this start tag token be the start tag token of the context node, e.g. for the purposes of determining if it is an HTML integration point.
+    // FIXME: 11. Create a start tag token whose name is the local name of context and whose attributes are the attributes of context.
+    //            Let this start tag token be the start tag token of context; e.g. for the purposes of determining if it is an HTML integration point.
 
-    // 11. Reset the parser's insertion mode appropriately.
+    // 12. Reset the parser's insertion mode appropriately.
     parser->reset_the_insertion_mode_appropriately();
 
-    // 12. Set the parser's form element pointer to the nearest node to the context element that is a form element
+    // 13. Set the HTML parser's form element pointer to the nearest node to context that is a form element
     //     (going straight up the ancestor chain, and including the element itself, if it is a form element), if any.
     //     (If there is no such form element, the form element pointer keeps its initial value, null.)
     parser->m_form_element = context_element.first_ancestor_of_type<HTMLFormElement>();
 
-    // 13. Place the input into the input stream for the HTML parser just created. The encoding confidence is irrelevant.
-    // 14. Start the parser and let it run until it has consumed all the characters just inserted into the input stream.
+    // 14. Place the input into the input stream for the HTML parser just created. The encoding confidence is irrelevant.
+    // 15. Start the HTML parser and let it run until it has consumed all the characters just inserted into the input stream.
     parser->run(context_element.document().url());
 
-    // 15. Return the child nodes of root, in tree order.
+    // 16. Return root's children, in tree order.
     Vector<GC::Root<DOM::Node>> children;
     while (GC::Ptr<DOM::Node> child = root->first_child()) {
         MUST(root->remove_child(*child));