LibWeb: Import new CSS parser

It's not finished or hooked up to anything yet, but let's get it into
the tree so we can continue working on it.

Original work by @stelar7.

Userland/Libraries/LibWeb/CSS/Parser/Parser.h

@@ -0,0 +1,107 @@
+/*
+ * Copyright (c) 2020-2021, SerenityOS developers
+ * 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/NonnullOwnPtrVector.h>
+#include <AK/Vector.h>
+#include <LibWeb/CSS/Parser/AtStyleRule.h>
+#include <LibWeb/CSS/Parser/DeclarationOrAtRule.h>
+#include <LibWeb/CSS/Parser/QualifiedStyleRule.h>
+#include <LibWeb/CSS/Parser/StyleBlockRule.h>
+#include <LibWeb/CSS/Parser/StyleComponentValueRule.h>
+#include <LibWeb/CSS/Parser/StyleDeclarationRule.h>
+#include <LibWeb/CSS/Parser/StyleFunctionRule.h>
+#include <LibWeb/CSS/Parser/Tokenizer.h>
+#include <LibWeb/CSS/Selector.h>
+
+namespace Web::CSS {
+
+class Parser {
+public:
+    Parser(const StringView& input, const String& encoding = "utf-8");
+    ~Parser();
+
+    // The normal parser entry point, for parsing stylesheets.
+    Vector<QualifiedStyleRule> parse_as_stylesheet();
+    // For the content of at-rules such as @media. It differs from "Parse a stylesheet" in the handling of <CDO-token> and <CDC-token>.
+    Vector<QualifiedStyleRule> parse_as_list_of_rules();
+    // For use by the CSSStyleSheet#insertRule method, and similar functions which might exist, which parse text into a single rule.
+    Optional<QualifiedStyleRule> parse_as_rule();
+    // Used in @supports conditions. [CSS3-CONDITIONAL]
+    Optional<StyleDeclarationRule> parse_as_declaration();
+    // For the contents of a style attribute, which parses text into the contents of a single style rule.
+    Vector<DeclarationOrAtRule> parse_as_list_of_declarations();
+    // For things that need to consume a single value, like the parsing rules for attr().
+    Optional<StyleComponentValueRule> parse_as_component_value();
+    // For the contents of presentational attributes, which parse text into a single declaration’s value, or for parsing a stand-alone selector [SELECT] or list of Media Queries [MEDIAQ], as in Selectors API or the media HTML attribute.
+    Vector<StyleComponentValueRule> parse_as_list_of_component_values();
+
+    Vector<StyleComponentValueRule> parse_as_list_of_comma_separated_component_values();
+
+    Vector<CSS::Selector::ComplexSelector> parse_selectors(Vector<String> parts);
+
+    // FIXME: https://www.w3.org/TR/selectors-4/
+    Optional<String> parse_a_selector() { return {}; }
+    Optional<String> parse_a_relative_selector() { return {}; }
+    bool match_a_selector_against_an_element() { return false; }
+    bool match_a_selector_against_a_pseudo_element() { return false; }
+    bool match_a_selector_against_a_tree() { return false; }
+
+    // FIXME: https://drafts.csswg.org/css-backgrounds-3/
+    static Optional<String> as_valid_background_repeat(String input) { return input; }
+    static Optional<String> as_valid_background_attachment(String input) { return input; }
+    static Optional<String> as_valid_background_position(String input) { return input; }
+    static Optional<String> as_valid_background_clip(String input) { return input; }
+    static Optional<String> as_valid_background_origin(String input) { return input; }
+    static Optional<String> as_valid_background_size(String input) { return input; }
+    static Optional<String> as_valid_border_style(String input) { return input; }
+    static Optional<String> as_valid_border_image_repeat(String input) { return input; }
+
+    void dump_all_tokens();
+
+private:
+    Token next_token();
+    Token peek_token();
+    Token current_token();
+    void reconsume_current_input_token();
+
+    Vector<QualifiedStyleRule> consume_a_list_of_rules(bool top_level);
+    AtStyleRule consume_an_at_rule();
+    Optional<QualifiedStyleRule> consume_a_qualified_rule();
+    Vector<DeclarationOrAtRule> consume_a_list_of_declarations();
+    Optional<StyleDeclarationRule> consume_a_declaration(Vector<StyleComponentValueRule>);
+    Optional<StyleDeclarationRule> consume_a_declaration();
+    StyleComponentValueRule consume_a_component_value();
+    StyleBlockRule consume_a_simple_block();
+    StyleFunctionRule consume_a_function();
+
+    Tokenizer m_tokenizer;
+    Vector<Token> m_tokens;
+    int m_iterator_offset { -1 };
+};
+
+}