mutating func lexMatchingOption()

in Sources/_MatchingEngine/Regex/Parse/LexicalAnalysis.swift [535:588]
41 lines of code
19 McCabe index (conditional complexity)

  mutating func lexMatchingOption() throws -> AST.MatchingOption? {
    typealias OptKind = AST.MatchingOption.Kind

    let locOpt = try recordLoc { src -> OptKind? in
      func advanceAndReturn(_ o: OptKind) -> OptKind {
        src.advance()
        return o
      }
      guard let c = src.peek() else { return nil }
      switch c {
      // PCRE options.
      case "i": return advanceAndReturn(.caseInsensitive)
      case "J": return advanceAndReturn(.allowDuplicateGroupNames)
      case "m": return advanceAndReturn(.multiline)
      case "n": return advanceAndReturn(.noAutoCapture)
      case "s": return advanceAndReturn(.singleLine)
      case "U": return advanceAndReturn(.reluctantByDefault)
      case "x":
        src.advance()
        return src.tryEat("x") ? .extraExtended : .extended

      // ICU options.
      case "w": return advanceAndReturn(.unicodeWordBoundaries)

      // Oniguruma options.
      case "D": return advanceAndReturn(.asciiOnlyDigit)
      case "P": return advanceAndReturn(.asciiOnlyPOSIXProps)
      case "S": return advanceAndReturn(.asciiOnlySpace)
      case "W": return advanceAndReturn(.asciiOnlyWord)
      case "y":
        src.advance()
        try src.expect("{")
        let opt: OptKind
        if src.tryEat("w") {
          opt = .textSegmentWordMode
        } else {
          try src.expect("g")
          opt = .textSegmentGraphemeMode
        }
        try src.expect("}")
        return opt

      // Swift semantic level options
      case "X": return advanceAndReturn(.graphemeClusterSemantics)
      case "u": return advanceAndReturn(.unicodeScalarSemantics)
      case "b": return advanceAndReturn(.byteSemantics)
        
      default:
        return nil
      }
    }
    guard let locOpt = locOpt else { return nil }
    return .init(locOpt.value, location: locOpt.location)
  }