Add support for rx'...' for experimental syntax

Author: hamishknight

Sources/_MatchingEngine/Regex/Parse/DelimiterLexing.swift

@@ -15,12 +15,14 @@ enum Delimiter: Hashable, CaseIterable {
   case traditional
   case experimental
   case reSingleQuote
+  case rxSingleQuote
 
   var openingAndClosing: (opening: String, closing: String) {
     switch self {
     case .traditional: return ("#/", "/#")
     case .experimental: return ("#|", "|#")
     case .reSingleQuote: return ("re'", "'")
+    case .rxSingleQuote: return ("rx'", "'")
     }
   }
   var opening: String { openingAndClosing.opening }
@@ -31,7 +33,7 @@ enum Delimiter: Hashable, CaseIterable {
     switch self {
     case .traditional, .reSingleQuote:
       return .traditional
-    case .experimental:
+    case .experimental, .rxSingleQuote:
       return .experimental
     }
   }
@@ -134,11 +136,11 @@ fileprivate struct DelimiterLexer {
   /// Attempt to skip over a closing delimiter character that is unlikely to be
   /// the actual closing delimiter.
   mutating func trySkipDelimiter(_ delimiter: Delimiter) {
-    // Only the closing `'` for re'...' can potentially be skipped over.
+    // Only the closing `'` for re'...'/rx'...' can potentially be skipped over.
     switch delimiter {
     case .traditional, .experimental:
       return
-    case .reSingleQuote:
+    case .reSingleQuote, .rxSingleQuote:
       break
     }
     guard load() == ascii("'") else { return }

Tests/RegexTests/ParseTests.swift

@@ -1497,6 +1497,9 @@ extension RegexTests {
     parseWithDelimitersTest("#/a b/#", concat("a", " ", "b"))
     parseWithDelimitersTest("#|a b|#", concat("a", "b"))
 
+    parseWithDelimitersTest("re'a b'", concat("a", " ", "b"))
+    parseWithDelimitersTest("rx'a b'", concat("a", "b"))
+
     parseWithDelimitersTest("#|[a b]|#", charClass("a", "b"))
     parseWithDelimitersTest(
       "#|(?-x)[a b]|#", changeMatchingOptions(
@@ -1537,6 +1540,9 @@ extension RegexTests {
       #"re'(?'a_bcA0-c1A'x*)'"#,
       balancedCapture(name: "a_bcA0", priorName: "c1A", zeroOrMore(of: "x")))
 
+    parseWithDelimitersTest(
+      #"rx' (?'a_bcA0' a b)'"#, concat(namedCapture("a_bcA0", concat("a", "b"))))
+
     parseWithDelimitersTest(
       #"re'(?('a_bcA0')x|y)'"#, conditional(
         .groupMatched(ref("a_bcA0")), trueBranch: "x", falseBranch: "y"))