From d2342caf426cecbeb3c28b77a7fa2e226228d385 Mon Sep 17 00:00:00 2001
From: Sam Atkins <atkinssj@gmail.com>
Date: Thu, 19 Aug 2021 15:45:15 +0100
Subject: [PATCH] LibWeb: Parse CSS builtins before other values

These are straightforward to parse, so doing them first saves
potentially expensive calculations inside parse_foo_value() functions.
---
 .../Libraries/LibWeb/CSS/Parser/Parser.cpp    | 19 ++++++++++++++++---
 Userland/Libraries/LibWeb/CSS/Parser/Parser.h |  3 ++-
 2 files changed, 18 insertions(+), 4 deletions(-)

diff --git a/Userland/Libraries/LibWeb/CSS/Parser/Parser.cpp b/Userland/Libraries/LibWeb/CSS/Parser/Parser.cpp
index e6a3d1dff6..b901115d80 100644
--- a/Userland/Libraries/LibWeb/CSS/Parser/Parser.cpp
+++ b/Userland/Libraries/LibWeb/CSS/Parser/Parser.cpp
@@ -1399,7 +1399,7 @@ Optional<float> Parser::try_parse_float(StringView string)
     return is_negative ? -value : value;
 }
 
-RefPtr<StyleValue> Parser::parse_builtin_or_dynamic_value(ParsingContext const& context, StyleComponentValueRule const& component_value)
+RefPtr<StyleValue> Parser::parse_builtin_value(ParsingContext const&, StyleComponentValueRule const& component_value)
 {
     if (component_value.is(Token::Type::Ident)) {
         auto ident = component_value.token().ident();
@@ -1410,6 +1410,11 @@ RefPtr<StyleValue> Parser::parse_builtin_or_dynamic_value(ParsingContext const&
         // FIXME: Implement `unset` keyword
     }
 
+    return {};
+}
+
+RefPtr<StyleValue> Parser::parse_dynamic_value(ParsingContext const& context, StyleComponentValueRule const& component_value)
+{
     if (component_value.is_function()) {
         auto& function = component_value.function();
 
@@ -2766,6 +2771,11 @@ RefPtr<StyleValue> Parser::parse_css_value(PropertyID property_id, TokenStream<S
     if (component_values.is_empty())
         return {};
 
+    if (component_values.size() == 1) {
+        if (auto parsed_value = parse_builtin_value(m_context, component_values.first()))
+            return parsed_value;
+    }
+
     // Special-case property handling
     switch (property_id) {
     case PropertyID::Background:
@@ -2875,8 +2885,11 @@ RefPtr<StyleValue> Parser::parse_css_value(ParsingContext const& context, Proper
         return LengthStyleValue::create(Length::make_px(strtof(string.characters(), nullptr)));
     }
 
-    if (auto builtin_or_dynamic = parse_builtin_or_dynamic_value(context, component_value))
-        return builtin_or_dynamic;
+    if (auto builtin = parse_builtin_value(context, component_value))
+        return builtin;
+
+    if (auto dynamic = parse_dynamic_value(context, component_value))
+        return dynamic;
 
     if (auto length = parse_length_value(context, component_value))
         return length;
diff --git a/Userland/Libraries/LibWeb/CSS/Parser/Parser.h b/Userland/Libraries/LibWeb/CSS/Parser/Parser.h
index f8d055410e..21fca4a7ac 100644
--- a/Userland/Libraries/LibWeb/CSS/Parser/Parser.h
+++ b/Userland/Libraries/LibWeb/CSS/Parser/Parser.h
@@ -168,7 +168,8 @@ private:
     static Optional<Length> parse_length(ParsingContext const&, StyleComponentValueRule const&);
     static Optional<URL> parse_url_function(ParsingContext const&, StyleComponentValueRule const&);
 
-    static RefPtr<StyleValue> parse_builtin_or_dynamic_value(ParsingContext const&, StyleComponentValueRule const&);
+    static RefPtr<StyleValue> parse_builtin_value(ParsingContext const&, StyleComponentValueRule const&);
+    static RefPtr<StyleValue> parse_dynamic_value(ParsingContext const&, StyleComponentValueRule const&);
     static RefPtr<StyleValue> parse_length_value(ParsingContext const&, StyleComponentValueRule const&);
     static RefPtr<StyleValue> parse_numeric_value(ParsingContext const&, StyleComponentValueRule const&);
     static RefPtr<StyleValue> parse_identifier_value(ParsingContext const&, StyleComponentValueRule const&);