[skip ci] Do not consume delimeter when not consuming component value (facebook#48841)

Summary:

Right now during parsing we can ask for a next component value, with a delimeter, and even if we don't have a component value to consume, we will consume the delimeter.

This is kind of awkward since e.g. trailing comma can be consumed, then we think syntax is valid. Let's try changing this.

Changelog: [Internal]

Reviewed By: lenaic

Differential Revision: D68474739

Author: NickGerleman

Diff for: packages/react-native/ReactCommon/react/renderer/css/CSSSyntaxParser.h

@@ -233,11 +233,14 @@ struct CSSComponentValueVisitorDispatcher {
   constexpr ReturnT consumeComponentValue(
       CSSDelimiter delimiter,
       const VisitorsT&... visitors) {
+    auto originalParser = parser;
     if (!consumeDelimiter(delimiter)) {
+      parser = originalParser;
       return {};
     }
 
     if (parser.peek().type() == parser.terminator_) {
+      parser = originalParser;
       return {};
     }
 

Diff for: packages/react-native/ReactCommon/react/renderer/css/tests/CSSSyntaxParserTest.cpp

@@ -579,4 +579,31 @@ TEST(CSSSyntaxParser, solidus_or_whitespace) {
   EXPECT_FALSE(delimValue1);
 }
 
+TEST(CSSSyntaxParser, delimeter_not_consumed_when_no_component_value) {
+  CSSSyntaxParser parser{"foo ,"};
+
+  auto identValue = parser.consumeComponentValue<std::string_view>(
+      [](const CSSPreservedToken& token) {
+        EXPECT_EQ(token.type(), CSSTokenType::Ident);
+        EXPECT_EQ(token.stringValue(), "foo");
+        return token.stringValue();
+      });
+
+  EXPECT_EQ(identValue, "foo");
+
+  auto identValue2 = parser.consumeComponentValue<bool>(
+      CSSDelimiter::Comma,
+      [](const CSSPreservedToken& /*token*/) { return true; });
+
+  EXPECT_FALSE(identValue2);
+
+  auto hasComma = parser.consumeComponentValue<bool>(
+      CSSDelimiter::Whitespace, [](const CSSPreservedToken& token) {
+        EXPECT_EQ(token.type(), CSSTokenType::Comma);
+        return true;
+      });
+
+  EXPECT_TRUE(hasComma);
+}
+
 } // namespace facebook::react