std::string likePatternToRe2()

in velox/functions/lib/Re2Functions.cpp [128:183]

• 52 lines of code
• 27 McCabe index (conditional complexity)

std::string likePatternToRe2(
    StringView pattern,
    std::optional<char> escapeChar,
    bool& validPattern) {
  std::string regex;
  validPattern = true;
  regex.reserve(pattern.size() * 2);
  regex.append("^");
  bool escaped = false;
  for (const char c : pattern) {
    if (escaped && !(c == '%' || c == '_' || c == escapeChar)) {
      validPattern = false;
    }
    if (!escaped && c == escapeChar) {
      escaped = true;
    } else {
      switch (c) {
        case '%':
          regex.append(escaped ? "%" : ".*");
          escaped = false;
          break;
        case '_':
          regex.append(escaped ? "_" : ".");
          escaped = false;
          break;
        // Escape all the meta characters in re2
        case '\\':
        case '|':
        case '^':
        case '$':
        case '.':
        case '*':
        case '+':
        case '?':
        case '(':
        case ')':
        case '[':
        case ']':
        case '{':
        case '}':
          regex.append("\\");
        // Append the meta character after the escape. Note: The fallthrough is
        // intentional.
        default:
          regex.append(1, c);
          escaped = false;
      }
    }
  }
  if (escaped) {
    validPattern = false;
  }

  regex.append("$");
  return regex;
}