From faba11f33c0e0ff93e9838e7005f7d813928dcc3 Mon Sep 17 00:00:00 2001
From: Sam Atkins <sam@ladybird.org>
Date: Mon, 1 Dec 2025 12:54:40 +0000
Subject: [PATCH] LibWeb/CSS: Pull out Supports::Declaration parsing

Avoid repeating this in two places.
---
 Libraries/LibWeb/CSS/Parser/Parser.cpp      | 26 +++++++++++++++------
 Libraries/LibWeb/CSS/Parser/Parser.h        |  1 +
 Libraries/LibWeb/CSS/Parser/RuleParsing.cpp |  6 ++---
 3 files changed, 22 insertions(+), 11 deletions(-)

diff --git a/Libraries/LibWeb/CSS/Parser/Parser.cpp b/Libraries/LibWeb/CSS/Parser/Parser.cpp
index d948eae5344..7fea2748ff9 100644
--- a/Libraries/LibWeb/CSS/Parser/Parser.cpp
+++ b/Libraries/LibWeb/CSS/Parser/Parser.cpp
@@ -335,14 +335,9 @@ OwnPtr<BooleanExpression> Parser::parse_supports_feature(TokenStream<ComponentVa
     // `<supports-decl> = ( <declaration> )`
     if (first_token.is_block() && first_token.block().is_paren()) {
         TokenStream block_tokens { first_token.block().value };
-        // FIXME: Parsing and then converting back to a string is weird.
-        if (auto declaration = consume_a_declaration(block_tokens); declaration.has_value() && !block_tokens.has_next_token()) {
+        if (auto declaration = parse_supports_declaration(block_tokens)) {
             transaction.commit();
-            auto supports_declaration = Supports::Declaration::create(
-                declaration->to_string(),
-                convert_to_style_property(*declaration).has_value());
-
-            return BooleanExpressionInParens::create(supports_declaration.release_nonnull<BooleanExpression>());
+            return BooleanExpressionInParens::create(declaration.release_nonnull<BooleanExpression>());
         }
     }
 
@@ -396,6 +391,23 @@ OwnPtr<BooleanExpression> Parser::parse_supports_feature(TokenStream<ComponentVa
     return {};
 }
 
+// https://drafts.csswg.org/css-conditional-5/#typedef-supports-decl
+OwnPtr<Supports::Declaration> Parser::parse_supports_declaration(TokenStream<ComponentValue>& tokens)
+{
+    // `<supports-decl> = ( <declaration> )`
+    // NB: Here, we only care about the <declaration> part.
+    auto transaction = tokens.begin_transaction();
+    tokens.discard_whitespace();
+    if (auto declaration = consume_a_declaration(tokens); declaration.has_value()) {
+        tokens.discard_whitespace();
+        if (!tokens.has_next_token()) {
+            transaction.commit();
+            return Supports::Declaration::create(declaration->to_string(), convert_to_style_property(*declaration).has_value());
+        }
+    }
+    return {};
+}
+
 // https://www.w3.org/TR/mediaqueries-4/#typedef-general-enclosed
 OwnPtr<GeneralEnclosed> Parser::parse_general_enclosed(TokenStream<ComponentValue>& tokens, MatchResult result)
 {
diff --git a/Libraries/LibWeb/CSS/Parser/Parser.h b/Libraries/LibWeb/CSS/Parser/Parser.h
index 42a16db4097..c4b3fe11242 100644
--- a/Libraries/LibWeb/CSS/Parser/Parser.h
+++ b/Libraries/LibWeb/CSS/Parser/Parser.h
@@ -564,6 +564,7 @@ private:
     OwnPtr<BooleanExpression> parse_boolean_expression_group(TokenStream<ComponentValue>&, MatchResult result_for_general_enclosed, ParseTest parse_test);
 
     OwnPtr<BooleanExpression> parse_supports_feature(TokenStream<ComponentValue>&);
+    OwnPtr<Supports::Declaration> parse_supports_declaration(TokenStream<ComponentValue>&);
 
     NonnullRefPtr<StyleValue const> resolve_unresolved_style_value(DOM::AbstractElement, GuardedSubstitutionContexts&, PropertyNameAndID const&, UnresolvedStyleValue const&);
 
diff --git a/Libraries/LibWeb/CSS/Parser/RuleParsing.cpp b/Libraries/LibWeb/CSS/Parser/RuleParsing.cpp
index a088669cb67..b438bd307eb 100644
--- a/Libraries/LibWeb/CSS/Parser/RuleParsing.cpp
+++ b/Libraries/LibWeb/CSS/Parser/RuleParsing.cpp
@@ -245,12 +245,10 @@ GC::Ptr<CSSImportRule> Parser::convert_to_import_rule(AtRule const& rule)
         supports = parse_a_supports(supports_tokens);
         if (!supports) {
             m_rule_context.append(RuleContext::SupportsCondition);
-            auto declaration = consume_a_declaration(supports_tokens);
+            auto supports_declaration = parse_supports_declaration(supports_tokens);
             m_rule_context.take_last();
-            if (declaration.has_value()) {
-                auto supports_declaration = Supports::Declaration::create(declaration->to_string(), convert_to_style_property(*declaration).has_value());
+            if (supports_declaration)
                 supports = Supports::create(supports_declaration.release_nonnull<BooleanExpression>());
-            }
         }
     }