From 34b3c094628e381d53c3a3caa6d77611d71217d0 Mon Sep 17 00:00:00 2001
From: Sam Atkins <atkinssj@serenityos.org>
Date: Wed, 30 Mar 2022 12:32:42 +0100
Subject: [PATCH] LibWeb: Spec-comment `parse_a_component_value()`

---
 .../Libraries/LibWeb/CSS/Parser/Parser.cpp    | 27 ++++++++++---------
 Userland/Libraries/LibWeb/CSS/Parser/Parser.h |  4 +--
 2 files changed, 16 insertions(+), 15 deletions(-)

diff --git a/Userland/Libraries/LibWeb/CSS/Parser/Parser.cpp b/Userland/Libraries/LibWeb/CSS/Parser/Parser.cpp
index 9a5b7a0ff6..5f506ef495 100644
--- a/Userland/Libraries/LibWeb/CSS/Parser/Parser.cpp
+++ b/Userland/Libraries/LibWeb/CSS/Parser/Parser.cpp
@@ -1979,31 +1979,32 @@ Vector<DeclarationOrAtRule> Parser::parse_a_list_of_declarations(TokenStream<T>&
     return consume_a_list_of_declarations(tokens);
 }
 
-Optional<StyleComponentValueRule> Parser::parse_as_component_value()
-{
-    return parse_a_component_value(m_token_stream);
-}
-
+// 5.3.9. Parse a component value
+// https://www.w3.org/TR/css-syntax-3/#parse-component-value
 template<typename T>
 Optional<StyleComponentValueRule> Parser::parse_a_component_value(TokenStream<T>& tokens)
 {
+    // To parse a component value from input:
+
+    // 1. Normalize input, and set input to the result.
+    // Note: This is done when initializing the Parser.
+
+    // 2. While the next input token from input is a <whitespace-token>, consume the next input token from input.
     tokens.skip_whitespace();
 
-    auto& token = tokens.peek_token();
-
-    if (token.is(Token::Type::EndOfFile)) {
+    // 3. If the next input token from input is an <EOF-token>, return a syntax error.
+    if (tokens.peek_token().is(Token::Type::EndOfFile))
         return {};
-    }
 
+    // 4. Consume a component value from input and let value be the return value.
     auto value = consume_a_component_value(tokens);
 
+    // 5. While the next input token from input is a <whitespace-token>, consume the next input token.
     tokens.skip_whitespace();
 
-    auto& maybe_eof = tokens.peek_token();
-    if (maybe_eof.is(Token::Type::EndOfFile)) {
+    // 6. If the next input token from input is an <EOF-token>, return value. Otherwise, return a syntax error.
+    if (tokens.peek_token().is(Token::Type::EndOfFile))
         return value;
-    }
-
     return {};
 }
 
diff --git a/Userland/Libraries/LibWeb/CSS/Parser/Parser.h b/Userland/Libraries/LibWeb/CSS/Parser/Parser.h
index 457d2bd3f4..66c178f9b3 100644
--- a/Userland/Libraries/LibWeb/CSS/Parser/Parser.h
+++ b/Userland/Libraries/LibWeb/CSS/Parser/Parser.h
@@ -89,8 +89,6 @@ public:
     Parser(ParsingContext const&, StringView input, String const& encoding = "utf-8");
     ~Parser() = default;
 
-    // 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<Vector<StyleComponentValueRule>> parse_as_comma_separated_list_of_component_values();
@@ -150,6 +148,8 @@ private:
     // "Parse a list of declarations" is for the contents of a style attribute, which parses text into the contents of a single style rule.
     template<typename T>
     Vector<DeclarationOrAtRule> parse_a_list_of_declarations(TokenStream<T>&);
+
+    // "Parse a component value" is for things that need to consume a single value, like the parsing rules for attr().
     template<typename T>
     Optional<StyleComponentValueRule> parse_a_component_value(TokenStream<T>&);
     template<typename T>