LibWeb/CSS: Add option to retain a Declaration's full source text

This will be needed by Supports, which expects declarations to serialize
verbatim.

Author: AtkinsSJ

Libraries/LibWeb/CSS/Parser/Parser.cpp

@@ -1042,7 +1042,7 @@ void Parser::consume_a_function_and_do_nothing(TokenStream<Token>& input)
 
 // https://drafts.csswg.org/css-syntax/#consume-declaration
 template<typename T>
-Optional<Declaration> Parser::consume_a_declaration(TokenStream<T>& input, Nested nested)
+Optional<Declaration> Parser::consume_a_declaration(TokenStream<T>& input, Nested nested, SaveOriginalText save_full_text)
 {
     // To consume a declaration from a token stream input, given an optional bool nested (default false):
 
@@ -1054,6 +1054,7 @@ Optional<Declaration> Parser::consume_a_declaration(TokenStream<T>& input, Neste
         .name {},
         .value {},
     };
+    auto start_token_index = input.current_index();
 
     // 1. If the next token is an <ident-token>, consume a token from input and set decl’s name to the token’s value.
     if (input.next_token().is(Token::Type::Ident)) {
@@ -1177,8 +1178,17 @@ Optional<Declaration> Parser::consume_a_declaration(TokenStream<T>& input, Neste
     }
 
     // 9. If decl is valid in the current context, return it; otherwise return nothing.
-    if (is_valid_in_the_current_context(declaration))
+    if (is_valid_in_the_current_context(declaration)) {
+        // AD-HOC: Assemble source tokens.
+        if (save_full_text == SaveOriginalText::Yes) {
+            StringBuilder original_full_text;
+            for (auto& token : input.tokens_since(start_token_index))
+                original_full_text.append(token.to_string());
+
+            declaration.original_full_text = original_full_text.to_string_without_validation();
+        }
         return declaration;
+    }
     return {};
 }
 
@@ -1929,8 +1939,8 @@ template Vector<RuleOrListOfDeclarations> Parser::consume_a_blocks_contents(Toke
 template Vector<ComponentValue> Parser::consume_a_list_of_component_values(TokenStream<ComponentValue>&, Optional<Token::Type>, Nested);
 template Vector<ComponentValue> Parser::consume_a_list_of_component_values(TokenStream<Token>&, Optional<Token::Type>, Nested);
 
-template Optional<Declaration> Parser::consume_a_declaration(TokenStream<Token>&, Nested);
-template Optional<Declaration> Parser::consume_a_declaration(TokenStream<ComponentValue>&, Nested);
+template Optional<Declaration> Parser::consume_a_declaration(TokenStream<Token>&, Nested, SaveOriginalText);
+template Optional<Declaration> Parser::consume_a_declaration(TokenStream<ComponentValue>&, Nested, SaveOriginalText);
 
 template void Parser::consume_the_remnants_of_a_bad_declaration(TokenStream<Token>&, Nested);
 template void Parser::consume_the_remnants_of_a_bad_declaration(TokenStream<ComponentValue>&, Nested);

Libraries/LibWeb/CSS/Parser/Parser.h

@@ -250,8 +250,12 @@ class Parser {
     Vector<RuleOrListOfDeclarations> consume_a_block(TokenStream<T>&);
     template<typename T>
     Vector<RuleOrListOfDeclarations> consume_a_blocks_contents(TokenStream<T>&);
+    enum class SaveOriginalText : u8 {
+        No,
+        Yes,
+    };
     template<typename T>
-    Optional<Declaration> consume_a_declaration(TokenStream<T>&, Nested = Nested::No);
+    Optional<Declaration> consume_a_declaration(TokenStream<T>&, Nested = Nested::No, SaveOriginalText = SaveOriginalText::No);
     template<typename T>
     void consume_the_remnants_of_a_bad_declaration(TokenStream<T>&, Nested);
     template<typename T>

Libraries/LibWeb/CSS/Parser/Types.h

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2024, Sam Atkins <sam@ladybird.org>
+ * Copyright (c) 2024-2025, Sam Atkins <sam@ladybird.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -8,6 +8,7 @@
 
 #include <AK/FlyString.h>
 #include <AK/Function.h>
+#include <AK/OwnPtr.h>
 #include <AK/Variant.h>
 #include <AK/Vector.h>
 #include <LibWeb/CSS/Parser/Token.h>
@@ -56,6 +57,7 @@ struct Declaration {
     Vector<ComponentValue> value;
     Important important = Important::No;
     Optional<String> original_value_text = {};
+    Optional<String> original_full_text = {};
 
     // FIXME: Only needed by our janky @supports re-serialization-re-parse code.
     String to_string() const;