LibWeb: Assert we're parsing a fragment on fragment cases

The specification says that parts labelled as a "fragment case" will
only occur when parsing a fragment. It says that if it occurs when
not parsing a fragment, then it is a specification error.

We should probably assume at this point that it's an implementation
error. This fixes a few little mistakes that were caught out by this.

Also moves the context element outside insertion mode reset,
as other (unimplemented) parts refer to it, such as
"adjusted current node".

Also cleans up insertion mode reset.

2 files changed, 68 insertions, 22 deletions

diff --git a/Libraries/LibWeb/Parser/HTMLDocumentParser.cpp b/Libraries/LibWeb/Parser/HTMLDocumentParser.cpp
index 83ac40917b..86182c075a 100644
--- a/Libraries/LibWeb/Parser/HTMLDocumentParser.cpp
+++ b/Libraries/LibWeb/Parser/HTMLDocumentParser.cpp
@@ -139,7 +139,7 @@ void HTMLDocumentParser::run(const URL& url)
 
         if (m_stop_parsing) {
 #ifdef PARSER_DEBUG
-            dbg() << "Stop parsing! :^)";
+            dbg() << "Stop parsing" << (m_parsing_fragment ? " fragment" : "") << "! :^)";
 #endif
             break;
         }
@@ -382,8 +382,10 @@ HTMLDocumentParser::AdjustedInsertionLocation HTMLDocumentParser::find_appropria
     if (m_foster_parenting && target.tag_name().is_one_of(HTML::TagNames::table, HTML::TagNames::tbody, HTML::TagNames::tfoot, HTML::TagNames::thead, HTML::TagNames::tr)) {
         // FIXME: There's a bunch of steps for <template> elements here.
         auto last_table = m_stack_of_open_elements.last_element_with_tag_name(HTML::TagNames::table);
-        if (!last_table)
+        if (!last_table) {
+            ASSERT(m_parsing_fragment);
             return { m_stack_of_open_elements.elements().first(), nullptr };
+        }
         if (last_table->parent_node())
             return { last_table->parent_node(), last_table };
         return { m_stack_of_open_elements.element_before(*last_table), nullptr };
@@ -772,7 +774,8 @@ void HTMLDocumentParser::handle_after_body(HTMLToken& token)
 
     if (token.is_end_tag() && token.tag_name() == HTML::TagNames::html) {
         if (m_parsing_fragment) {
-            TODO();
+            PARSE_ERROR();
+            return;
         }
         m_insertion_mode = InsertionMode::AfterAfterBody;
         return;
@@ -1053,20 +1056,33 @@ void HTMLDocumentParser::handle_in_body(HTMLToken& token)
     if (token.is_start_tag() && token.tag_name() == HTML::TagNames::body) {
         PARSE_ERROR();
         if (m_stack_of_open_elements.elements().size() == 1
-            || node_before_current_node().tag_name() != HTML::TagNames::body
+            || m_stack_of_open_elements.elements().at(1).tag_name() != HTML::TagNames::body
             || m_stack_of_open_elements.contains(HTML::TagNames::template_)) {
+            ASSERT(m_parsing_fragment);
             return;
         }
         m_frameset_ok = false;
+        auto& body_element = m_stack_of_open_elements.elements().at(1);
         for (auto& attribute : token.m_tag.attributes) {
-            if (node_before_current_node().has_attribute(attribute.local_name_builder.string_view()))
+            if (body_element.has_attribute(attribute.local_name_builder.string_view()))
                 continue;
-            node_before_current_node().set_attribute(attribute.local_name_builder.to_string(), attribute.value_builder.to_string());
+            body_element.set_attribute(attribute.local_name_builder.to_string(), attribute.value_builder.to_string());
         }
         return;
     }
 
     if (token.is_start_tag() && token.tag_name() == HTML::TagNames::frameset) {
+        PARSE_ERROR();
+
+        if (m_stack_of_open_elements.elements().size() == 1
+            || m_stack_of_open_elements.elements().at(1).tag_name() != HTML::TagNames::body) {
+            ASSERT(m_parsing_fragment);
+            return;
+        }
+
+        if (!m_frameset_ok)
+            return;
+
         TODO();
     }
 
@@ -1823,18 +1839,27 @@ void HTMLDocumentParser::clear_the_stack_back_to_a_table_context()
 {
     while (!current_node().tag_name().is_one_of(HTML::TagNames::table, HTML::TagNames::template_, HTML::TagNames::html))
         m_stack_of_open_elements.pop();
+
+    if (current_node().tag_name() == HTML::TagNames::html)
+        ASSERT(m_parsing_fragment);
 }
 
 void HTMLDocumentParser::clear_the_stack_back_to_a_table_row_context()
 {
     while (!current_node().tag_name().is_one_of(HTML::TagNames::tr, HTML::TagNames::template_, HTML::TagNames::html))
         m_stack_of_open_elements.pop();
+
+    if (current_node().tag_name() == HTML::TagNames::html)
+        ASSERT(m_parsing_fragment);
 }
 
 void HTMLDocumentParser::clear_the_stack_back_to_a_table_body_context()
 {
     while (!current_node().tag_name().is_one_of(HTML::TagNames::tbody, HTML::TagNames::tfoot, HTML::TagNames::thead, HTML::TagNames::template_, HTML::TagNames::html))
         m_stack_of_open_elements.pop();
+
+    if (current_node().tag_name() == HTML::TagNames::html)
+        ASSERT(m_parsing_fragment);
 }
 
 void HTMLDocumentParser::handle_in_row(HTMLToken& token)
@@ -1928,7 +1953,8 @@ void HTMLDocumentParser::handle_in_cell(HTMLToken& token)
         return;
     }
     if (token.is_start_tag() && token.tag_name().is_one_of(HTML::TagNames::caption, HTML::TagNames::col, HTML::TagNames::colgroup, HTML::TagNames::tbody, HTML::TagNames::td, HTML::TagNames::tfoot, HTML::TagNames::th, HTML::TagNames::thead, HTML::TagNames::tr)) {
-        if (!m_stack_of_open_elements.has_in_table_scope(HTML::TagNames::td) && m_stack_of_open_elements.has_in_table_scope(HTML::TagNames::th)) {
+        if (!m_stack_of_open_elements.has_in_table_scope(HTML::TagNames::td) && !m_stack_of_open_elements.has_in_table_scope(HTML::TagNames::th)) {
+            ASSERT(m_parsing_fragment);
             PARSE_ERROR();
             return;
         }
@@ -2268,6 +2294,7 @@ void HTMLDocumentParser::handle_in_select(HTMLToken& token)
 
     if (token.is_end_tag() && token.tag_name() == HTML::TagNames::select) {
         if (!m_stack_of_open_elements.has_in_select_scope(HTML::TagNames::select)) {
+            ASSERT(m_parsing_fragment);
             PARSE_ERROR();
             return;
         }
@@ -2279,8 +2306,10 @@ void HTMLDocumentParser::handle_in_select(HTMLToken& token)
     if (token.is_start_tag() && token.tag_name() == HTML::TagNames::select) {
         PARSE_ERROR();
 
-        if (!m_stack_of_open_elements.has_in_select_scope(HTML::TagNames::select))
+        if (!m_stack_of_open_elements.has_in_select_scope(HTML::TagNames::select)) {
+            ASSERT(m_parsing_fragment);
             return;
+        }
 
         m_stack_of_open_elements.pop_until_an_element_with_tag_name_has_been_popped(HTML::TagNames::select);
         reset_the_insertion_mode_appropriately();
@@ -2291,6 +2320,7 @@ void HTMLDocumentParser::handle_in_select(HTMLToken& token)
         PARSE_ERROR();
 
         if (!m_stack_of_open_elements.has_in_select_scope(HTML::TagNames::select)) {
+            ASSERT(m_parsing_fragment);
             return;
         }
 
@@ -2322,6 +2352,7 @@ void HTMLDocumentParser::handle_in_caption(HTMLToken& token)
 {
     if (token.is_end_tag() && token.tag_name() == HTML::TagNames::caption) {
         if (!m_stack_of_open_elements.has_in_table_scope(HTML::TagNames::caption)) {
+            ASSERT(m_parsing_fragment);
             PARSE_ERROR();
             return;
         }
@@ -2341,6 +2372,7 @@ void HTMLDocumentParser::handle_in_caption(HTMLToken& token)
     if ((token.is_start_tag() && token.tag_name().is_one_of(HTML::TagNames::caption, HTML::TagNames::col, HTML::TagNames::colgroup, HTML::TagNames::tbody, HTML::TagNames::td, HTML::TagNames::tfoot, HTML::TagNames::th, HTML::TagNames::thead, HTML::TagNames::tr))
         || (token.is_end_tag() && token.tag_name() == HTML::TagNames::table)) {
         if (!m_stack_of_open_elements.has_in_table_scope(HTML::TagNames::caption)) {
+            ASSERT(m_parsing_fragment);
             PARSE_ERROR();
             return;
         }
@@ -2495,11 +2527,12 @@ void HTMLDocumentParser::handle_in_template(HTMLToken& token)
 
     if (token.is_end_of_file()) {
         if (!m_stack_of_open_elements.contains(HTML::TagNames::template_)) {
+            ASSERT(m_parsing_fragment);
             stop_parsing();
-        } else {
-            PARSE_ERROR();
+            return;
         }
 
+        PARSE_ERROR();
         m_stack_of_open_elements.pop_until_an_element_with_tag_name_has_been_popped(HTML::TagNames::template_);
         m_list_of_active_formatting_elements.clear_up_to_the_last_marker();
         m_stack_of_template_insertion_modes.take_last();
@@ -2540,7 +2573,7 @@ void HTMLDocumentParser::handle_in_frameset(HTMLToken& token)
 
         m_stack_of_open_elements.pop();
 
-        if (m_parsing_fragment && current_node().tag_name() != HTML::TagNames::frameset) {
+        if (!m_parsing_fragment && current_node().tag_name() != HTML::TagNames::frameset) {
             m_insertion_mode = InsertionMode::AfterFrameset;
         }
         return;
@@ -2634,14 +2667,14 @@ void HTMLDocumentParser::handle_after_after_frameset(HTMLToken& token)
     PARSE_ERROR();
 }
 
-void HTMLDocumentParser::reset_the_insertion_mode_appropriately(const Element* context_element)
+void HTMLDocumentParser::reset_the_insertion_mode_appropriately()
 {
     for (ssize_t i = m_stack_of_open_elements.elements().size() - 1; i >= 0; --i) {
-
+        bool last = i == 0;
         // NOTE: When parsing fragments, we substitute the context element for the root of the stack of open elements.
         RefPtr<Element> node;
-        if (i == 0 && context_element) {
-            node = context_element;
+        if (last && m_parsing_fragment) {
+            node = m_context_element;
         } else {
             node = m_stack_of_open_elements.elements().at(i);
         }
@@ -2650,7 +2683,7 @@ void HTMLDocumentParser::reset_the_insertion_mode_appropriately(const Element* c
             TODO();
         }
 
-        if (node->tag_name().is_one_of(HTML::TagNames::td, HTML::TagNames::th)) {
+        if (!last && node->tag_name().is_one_of(HTML::TagNames::td, HTML::TagNames::th)) {
             m_insertion_mode = InsertionMode::InCell;
             return;
         }
@@ -2684,24 +2717,35 @@ void HTMLDocumentParser::reset_the_insertion_mode_appropriately(const Element* c
             TODO();
         }
 
+        if (!last && node->tag_name() == HTML::TagNames::head) {
+            m_insertion_mode = InsertionMode::InHead;
+            return;
+        }
+
         if (node->tag_name() == HTML::TagNames::body) {
             m_insertion_mode = InsertionMode::InBody;
             return;
         }
 
         if (node->tag_name() == HTML::TagNames::frameset) {
+            ASSERT(m_parsing_fragment);
             m_insertion_mode = InsertionMode::InFrameset;
-            if (m_parsing_fragment) {
-                TODO();
-            }
             return;
         }
 
         if (node->tag_name() == HTML::TagNames::html) {
-            TODO();
+            if (!m_head_element) {
+                ASSERT(m_parsing_fragment);
+                m_insertion_mode = InsertionMode::BeforeHead;
+                return;
+            }
+
+            m_insertion_mode = InsertionMode::AfterHead;
+            return;
         }
     }
 
+    ASSERT(m_parsing_fragment);
     m_insertion_mode = InsertionMode::InBody;
 }
 
@@ -2725,6 +2769,7 @@ Document& HTMLDocumentParser::document()
 NonnullRefPtrVector<Node> HTMLDocumentParser::parse_html_fragment(Element& context_element, const StringView& markup)
 {
     HTMLDocumentParser parser(markup, "utf-8");
+    parser.m_context_element = context_element;
     parser.m_parsing_fragment = true;
     parser.document().set_quirks_mode(context_element.document().mode());
 
@@ -2751,7 +2796,7 @@ NonnullRefPtrVector<Node> HTMLDocumentParser::parse_html_fragment(Element& conte
 
     // FIXME: Create a start tag token whose name is the local name of context and whose attributes are the attributes of context.
 
-    parser.reset_the_insertion_mode_appropriately(&context_element);
+    parser.reset_the_insertion_mode_appropriately();
 
     for (auto* form_candidate = &context_element; form_candidate; form_candidate = form_candidate->parent_element()) {
         if (is<HTMLFormElement>(*form_candidate)) {
diff --git a/Libraries/LibWeb/Parser/HTMLDocumentParser.h b/Libraries/LibWeb/Parser/HTMLDocumentParser.h
index ec710a2f0d..1d2fbf2f5c 100644
--- a/Libraries/LibWeb/Parser/HTMLDocumentParser.h
+++ b/Libraries/LibWeb/Parser/HTMLDocumentParser.h
@@ -138,7 +138,7 @@ private:
     void increment_script_nesting_level();
     void decrement_script_nesting_level();
     size_t script_nesting_level() const { return m_script_nesting_level; }
-    void reset_the_insertion_mode_appropriately(const Element* context_element = nullptr);
+    void reset_the_insertion_mode_appropriately();
 
     void adjust_mathml_attributes(HTMLToken&);
     void adjust_svg_attributes(HTMLToken&);
@@ -177,6 +177,7 @@ private:
     RefPtr<Document> m_document;
     RefPtr<HTMLHeadElement> m_head_element;
     RefPtr<HTMLFormElement> m_form_element;
+    RefPtr<Element> m_context_element;
 
     Vector<HTMLToken> m_pending_table_character_tokens;