LibWeb: Factor out the "stack of open elements" into its own class

This will allow us to write more expressive parsing code. :^)

Libraries/LibWeb/CMakeLists.txt

@@ -88,6 +88,7 @@ set(SOURCES
     Parser/HTMLParser.cpp
     Parser/HTMLToken.cpp
     Parser/HTMLTokenizer.cpp
+    Parser/StackOfOpenElements.cpp
     ResourceLoader.cpp
     StylePropertiesModel.cpp
     URLEncoder.cpp

Libraries/LibWeb/Parser/HTMLDocumentParser.cpp

@@ -109,21 +109,21 @@ void HTMLDocumentParser::handle_before_html(HTMLToken& token)
     if (token.is_start_tag() && token.tag_name() == "html") {
         auto element = create_element_for(token);
         document().append_child(element);
-        m_stack_of_open_elements.append(element);
+        m_stack_of_open_elements.push(move(element));
         m_insertion_mode = InsertionMode::BeforeHead;
         return;
     }
     ASSERT_NOT_REACHED();
 }
 
-NonnullRefPtr<Node> HTMLDocumentParser::current_node()
+Element& HTMLDocumentParser::current_node()
 {
-    return m_stack_of_open_elements.last();
+    return m_stack_of_open_elements.current_node();
 }
 
 RefPtr<Node> HTMLDocumentParser::find_appropriate_place_for_inserting_node()
 {
-    auto target = current_node();
+    auto& target = current_node();
     if (m_foster_parenting) {
         ASSERT_NOT_REACHED();
     }
@@ -145,7 +145,7 @@ RefPtr<Element> HTMLDocumentParser::insert_html_element(HTMLToken& token)
     auto element = create_element_for(token);
     // FIXME: Check if it's possible to insert `element` at `adjusted_insertion_location`
     adjusted_insertion_location->append_child(element);
-    m_stack_of_open_elements.append(element);
+    m_stack_of_open_elements.push(element);
     return element;
 }
 
@@ -164,14 +164,14 @@ void HTMLDocumentParser::handle_in_head(HTMLToken& token)
 {
     if (token.is_start_tag() && token.tag_name() == "meta") {
         auto element = insert_html_element(token);
-        m_stack_of_open_elements.take_last();
+        m_stack_of_open_elements.pop();
         if (token.is_self_closing()) {
             ASSERT_NOT_REACHED();
         }
         return;
     }
     if (token.is_end_tag() && token.tag_name() == "head") {
-        m_stack_of_open_elements.take_last();
+        m_stack_of_open_elements.pop();
         m_insertion_mode = InsertionMode::AfterHead;
         return;
     }
@@ -243,21 +243,8 @@ AnythingElse:
 void HTMLDocumentParser::generate_implied_end_tags()
 {
     Vector<String> names { "dd", "dt", "li", "optgroup", "option", "p", "rb", "rp", "rt", "rtc" };
-    while (names.contains_slow(current_node()->tag_name()))
-        m_stack_of_open_elements.take_last();
-}
-
-bool HTMLDocumentParser::stack_of_open_elements_has_element_with_tag_name_in_scope(const FlyString& tag_name)
-{
-    Vector<String> list { "applet", "caption", "html", "table", "td", "th", "marquee", "object", "template" };
-    for (ssize_t i = m_stack_of_open_elements.size() - 1; i >= 0; --i) {
-        auto& node = m_stack_of_open_elements.at(i);
-        if (node.tag_name() == tag_name)
-            return true;
-        if (list.contains_slow(node.tag_name()))
-            return false;
-    }
-    ASSERT_NOT_REACHED();
+    while (names.contains_slow(current_node().tag_name()))
+        m_stack_of_open_elements.pop();
 }
 
 void HTMLDocumentParser::handle_after_body(HTMLToken& token)
@@ -284,7 +271,7 @@ void HTMLDocumentParser::handle_after_after_body(HTMLToken& token)
 void HTMLDocumentParser::handle_in_body(HTMLToken& token)
 {
     if (token.is_end_tag() && token.tag_name() == "body") {
-        if (!stack_of_open_elements_has_element_with_tag_name_in_scope("body")) {
+        if (!m_stack_of_open_elements.has_in_scope("body")) {
             ASSERT_NOT_REACHED();
         }
 
@@ -310,17 +297,17 @@ void HTMLDocumentParser::handle_in_body(HTMLToken& token)
         if (token.is_end_tag() && names.contains_slow(token.tag_name())) {
             // FIXME: If the stack of open elements has a p element in button scope, then close a p element.
 
-            if (!stack_of_open_elements_has_element_with_tag_name_in_scope(token.tag_name())) {
+            if (!m_stack_of_open_elements.has_in_scope(token.tag_name())) {
                 ASSERT_NOT_REACHED();
             }
 
             generate_implied_end_tags();
 
-            if (current_node()->tag_name() != token.tag_name()) {
+            if (current_node().tag_name() != token.tag_name()) {
                 ASSERT_NOT_REACHED();
             }
 
-            m_stack_of_open_elements.take_last();
+            m_stack_of_open_elements.pop();
             return;
         }
     }

Libraries/LibWeb/Parser/HTMLDocumentParser.h

@@ -29,6 +29,7 @@
 #include <AK/NonnullRefPtrVector.h>
 #include <LibWeb/DOM/Node.h>
 #include <LibWeb/Parser/HTMLTokenizer.h>
+#include <LibWeb/Parser/StackOfOpenElements.h>
 
 #define ENUMERATE_INSERTION_MODES               \
     __ENUMERATE_INSERTION_MODE(Initial)         \
@@ -93,10 +94,10 @@ private:
     NonnullRefPtr<Element> create_element_for(HTMLToken&);
     RefPtr<Node> find_appropriate_place_for_inserting_node();
     RefPtr<Element> insert_html_element(HTMLToken&);
-    NonnullRefPtr<Node> current_node();
+    Element& current_node();
 
     InsertionMode m_insertion_mode { InsertionMode::Initial };
-    NonnullRefPtrVector<Node> m_stack_of_open_elements;
+    StackOfOpenElements m_stack_of_open_elements;
 
     HTMLTokenizer m_tokenizer;
 

Libraries/LibWeb/Parser/StackOfOpenElements.cpp

@@ -0,0 +1,23 @@
+#include <LibWeb/DOM/Element.h>
+#include <LibWeb/Parser/StackOfOpenElements.h>
+
+namespace Web {
+
+StackOfOpenElements::~StackOfOpenElements()
+{
+}
+
+bool StackOfOpenElements::has_in_scope(const FlyString& tag_name) const
+{
+    static Vector<FlyString> list { "applet", "caption", "html", "table", "td", "th", "marquee", "object", "template" };
+    for (ssize_t i = m_elements.size() - 1; i >= 0; --i) {
+        auto& node = m_elements.at(i);
+        if (node.tag_name() == tag_name)
+            return true;
+        if (list.contains_slow(node.tag_name()))
+            return false;
+    }
+    ASSERT_NOT_REACHED();
+}
+
+}

Libraries/LibWeb/Parser/StackOfOpenElements.h

@@ -0,0 +1,53 @@
+/*
+ * Copyright (c) 2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <AK/NonnullRefPtrVector.h>
+#include <LibWeb/DOM/Element.h>
+#include <LibWeb/Forward.h>
+
+namespace Web {
+
+class StackOfOpenElements {
+public:
+    StackOfOpenElements() { }
+    ~StackOfOpenElements();
+
+    bool is_empty() const { return m_elements.is_empty(); }
+    void push(NonnullRefPtr<Element> element) { m_elements.append(move(element)); }
+    NonnullRefPtr<Element> pop() { return m_elements.take_last(); }
+
+    const Element& current_node() const { return m_elements.last(); }
+    Element& current_node() { return m_elements.last(); }
+
+    bool has_in_scope(const FlyString& tag_name) const;
+
+private:
+    NonnullRefPtrVector<Element> m_elements;
+};
+
+}