// returns pair(regexp, vars)
static Pair<S, LS> dollarVarsToRegexp_generic(S replacement, S s) {
  new L<S> varNames_out;
  L<S> tok = javaTok(s);
  int j = 0;
  for (int i = 1; i < l(tok); i += 2) {
    S t = tok.get(i);
    if (isDollarVar(t)) {
      replaceTokens(tok, j, i, regexpQuote(joinSubList(tok, j, i)));
      listAdd(varNames_out, t);
      tok.set(i, replacement);
      j = i+1;
    }
  }
  replaceTokens(tok, j, l(tok), regexpQuote(joinSubList(tok, j)));
  ret pair(join(tok), varNames_out);
}

Began life as a copy of #1024301