Function IsAnchorEnd

extern/re2/re2/compile.cc:1012–1054

Is this regexp required to start at the end of the text? Only approximate; can return false for complicated regexps like (a\z|b\z), but handles ((a|b)\z). Could use the Walker to write a more exact one.

// Only approximate; can return false for complicated regexps like (a\z|b\z),
// but handles ((a|b)\z).  Could use the Walker to write a more exact one.
static bool IsAnchorEnd(Regexp** pre, int depth) {
  Regexp* re = *pre;
  Regexp* sub;
  // The depth limit makes sure that we don't overflow
  // the stack on a deeply nested regexp.  As the comment
  // above says, IsAnchorEnd is conservative, so returning
  // a false negative is okay.  The exact limit is somewhat arbitrary.
  if (re == NULL || depth >= 4)
    return false;
  switch (re->op()) {
    default:
      break;
    case kRegexpConcat:
      if (re->nsub() > 0) {
        sub = re->sub()[re->nsub() - 1]->Incref();
        if (IsAnchorEnd(&sub, depth+1)) {
          PODArray<Regexp*> subcopy(re->nsub());
          subcopy[re->nsub() - 1] = sub;  // already have reference
          for (int i = 0; i < re->nsub() - 1; i++)
            subcopy[i] = re->sub()[i]->Incref();
          *pre = Regexp::Concat(subcopy.data(), re->nsub(), re->parse_flags());
          re->Decref();
          return true;
        }
        sub->Decref();
      }
      break;
    case kRegexpCapture:
      sub = re->sub()[0]->Incref();
      if (IsAnchorEnd(&sub, depth+1)) {
        *pre = Regexp::Capture(sub, re->parse_flags(), re->cap());
        re->Decref();
        return true;
      }
      sub->Decref();
      break;
    case kRegexpEndText:
      *pre = Regexp::LiteralString(NULL, 0, re->parse_flags());
      re->Decref();
      return true;
  }
  return false;
}

void Compiler::Setup(Regexp::ParseFlags flags, int64_t max_mem,
                     RE2::Anchor anchor) {