Fix the definition of SyntaxOptions.experimental

This shouldn't include e.g `namedCapturesOnly`.

Author: hamishknight

Sources/_RegexParser/Regex/Parse/SyntaxOptions.swift

@@ -76,8 +76,8 @@ public struct SyntaxOptions: OptionSet {
   public static var traditional: Self { Self(0) }
 
   public static var experimental: Self {
-    // Experimental syntax enables everything except end-of-line comments.
-    Self(~0).subtracting(.endOfLineComments)
+    [.nonSemanticWhitespace, .experimentalQuotes, .experimentalComments,
+     .experimentalRanges, .experimentalCaptures]
   }
 
   // TODO: Probably want to model strict-PCRE etc. options too.

Tests/RegexTests/ParseTests.swift

@@ -770,6 +770,9 @@ extension RegexTests {
               syntax: .experimental)
     parseTest(#""\"""#, quote("\""), syntax: .experimental)
 
+    parseTest(#"(abc)"#, capture(concat("a", "b", "c")),
+              syntax: .experimental, captures: [.cap])
+
     // Quotes in character classes.
     parseTest(#"[\Q-\E]"#, charClass(quote_m("-")))
     parseTest(#"[\Qa-b[[*+\\E]"#, charClass(quote_m("a-b[[*+\\")))