Class Parser

java/com/google/re2j/Parser.java:25–1730

A parser of regular expression patterns. The only public entry point is #parse(String pattern, int flags).

 * The only public entry point is {@link #parse(String pattern, int flags)}.
 */
class Parser {

  // Unexpected error
  private static final String ERR_INTERNAL_ERROR = "regexp/syntax: internal error";

  // Parse errors
  private static final String ERR_INVALID_CHAR_RANGE = "invalid character class range";
  private static final String ERR_INVALID_ESCAPE = "invalid escape sequence";
  private static final String ERR_INVALID_NAMED_CAPTURE = "invalid named capture";
  private static final String ERR_INVALID_PERL_OP = "invalid or unsupported Perl syntax";
  private static final String ERR_INVALID_REPEAT_OP = "invalid nested repetition operator";
  private static final String ERR_INVALID_REPEAT_SIZE = "invalid repeat count";
  private static final String ERR_MISSING_BRACKET = "missing closing ]";
  private static final String ERR_MISSING_PAREN = "missing closing )";
  private static final String ERR_MISSING_REPEAT_ARGUMENT =
      "missing argument to repetition operator";
  private static final String ERR_TRAILING_BACKSLASH = "trailing backslash at end of expression";
  private static final String ERR_DUPLICATE_NAMED_CAPTURE = "duplicate capture group name";

  // Hack to expose ArrayList.removeRange().
  private static class Stack extends ArrayList<Regexp> {
    @Override
    public void removeRange(int fromIndex, int toIndex) {
      super.removeRange(fromIndex, toIndex);
    }
  }

  private final String wholeRegexp;
  // Flags control the behavior of the parser and record information about
  // regexp context.
  private int flags; // parse mode flags

  // Stack of parsed expressions.
  private final Stack stack = new Stack();
  private Regexp free;
  private int numCap = 0; // number of capturing groups seen
  private final Map<String, Integer> namedGroups = new HashMap<String, Integer>();

  Parser(String wholeRegexp, int flags) {
    this.wholeRegexp = wholeRegexp;
    this.flags = flags;
  }

  // Allocate a Regexp, from the free list if possible.
  private Regexp newRegexp(Regexp.Op op) {
    Regexp re = free;
    if (re != null && re.subs != null && re.subs.length > 0) {
      free = re.subs[0];
      re.reinit();
      re.op = op;
    } else {
      re = new Regexp(op);
    }
    return re;
  }

  private void reuse(Regexp re) {
    if (re.subs != null && re.subs.length > 0) {