Function ParseEscape

extern/re2/re2/parse.cc:1449–1596

Parse an escape sequence (e.g., \n, \{). Sets *s to span the remainder of the string. Sets *rp to the named character.

// Sets *s to span the remainder of the string.
// Sets *rp to the named character.
static bool ParseEscape(StringPiece* s, Rune* rp,
                        RegexpStatus* status, int rune_max) {
  const char* begin = s->data();
  if (s->empty() || (*s)[0] != '\\') {
    // Should not happen - caller always checks.
    status->set_code(kRegexpInternalError);
    status->set_error_arg(StringPiece());
    return false;
  }
  if (s->size() == 1) {
    status->set_code(kRegexpTrailingBackslash);
    status->set_error_arg(StringPiece());
    return false;
  }
  Rune c, c1;
  s->remove_prefix(1);  // backslash
  if (StringPieceToRune(&c, s, status) < 0)
    return false;
  int code;
  switch (c) {
    default:
      if (c < Runeself && !isalpha(c) && !isdigit(c)) {
        // Escaped non-word characters are always themselves.
        // PCRE is not quite so rigorous: it accepts things like
        // \q, but we don't.  We once rejected \_, but too many
        // programs and people insist on using it, so allow \_.
        *rp = c;
        return true;
      }
      goto BadEscape;

    // Octal escapes.
    case '1':
    case '2':
    case '3':
    case '4':
    case '5':
    case '6':
    case '7':
      // Single non-zero octal digit is a backreference; not supported.
      if (s->empty() || (*s)[0] < '0' || (*s)[0] > '7')
        goto BadEscape;
      FALLTHROUGH_INTENDED;
    case '0':
      // consume up to three octal digits; already have one.
      code = c - '0';
      if (!s->empty() && '0' <= (c = (*s)[0]) && c <= '7') {
        code = code * 8 + c - '0';
        s->remove_prefix(1);  // digit
        if (!s->empty()) {
          c = (*s)[0];
          if ('0' <= c && c <= '7') {
            code = code * 8 + c - '0';
            s->remove_prefix(1);  // digit
          }
        }
      }
      if (code > rune_max)