Method parsePerlFlags

java/com/google/re2j/Parser.java:1040–1144

(StringIterator t)

  // Pre: t at "(?".  Post: t after ")".
  // Sets numCap.
  private void parsePerlFlags(StringIterator t) throws PatternSyntaxException {
    int startPos = t.pos();

    // Check for named captures, first introduced in Python's regexp library.
    // As usual, there are three slightly different syntaxes:
    //
    //   (?P<name>expr)   the original, introduced by Python
    //   (?<name>expr)    the .NET alteration, adopted by Perl 5.10
    //   (?'name'expr)    another .NET alteration, adopted by Perl 5.10
    //
    // Perl 5.10 gave in and implemented the Python version too,
    // but they claim that the last two are the preferred forms.
    // PCRE and languages based on it (specifically, PHP and Ruby)
    // support all three as well.  EcmaScript 4 uses only the Python form.
    //
    // In both the open source world (via Code Search) and the
    // Google source tree, (?P<name>expr) and (?<name>expr) are the
    // dominant forms of named captures and both are supported.
    String s = t.rest();
    if (s.startsWith("(?P<") || s.startsWith("(?<")) {
      // Pull out name.
      int begin = s.charAt(2) == 'P' ? 4 : 3;
      int end = s.indexOf('>', begin);
      if (end < 0) {
        throw new PatternSyntaxException(ERR_INVALID_NAMED_CAPTURE, s);
      }
      String name = s.substring(begin, end); // "name"
      t.skipString(name);
      t.skip(begin + 1); // "(?P<>" or "(?<>"
      if (!isValidCaptureName(name)) {
        throw new PatternSyntaxException(
            ERR_INVALID_NAMED_CAPTURE, s.substring(0, end + 1)); // "(?P<name>" or "(?<name>"
      }
      // Like ordinary capture, but named.
      Regexp re = op(Regexp.Op.LEFT_PAREN);
      re.cap = ++numCap;
      if (namedGroups.put(name, numCap) != null) {
        throw new PatternSyntaxException(ERR_DUPLICATE_NAMED_CAPTURE, name);
      }
      re.name = name;
      return;
    }

    // Non-capturing group.  Might also twiddle Perl flags.
    t.skip(2); // "(?"
    int flags = this.flags;
    int sign = +1;
    boolean sawFlag = false;
    loop:
    while (t.more()) {
      int c = t.pop();
      switch (c) {
        default:
          break loop;

          // Flags.
        case 'i':
          flags |= RE2.FOLD_CASE;