sbool tok_doubleFor_v2_debug;

static void tok_doubleFor_v2(L<S> tok) {
  for (int i : reversed(indexesOf(tok, "for"))) {
    if (neq(get(tok, i+2), "(")) continue;
    int argsFrom = i+4;
    // move loop label to proper place
    if (eqGet(tok, i-2, ":") && isIdentifier(get(tok, i-4))) i -= 4;
    int iColon = indexOfAny(tok, argsFrom, ":", ")");
    if (neq(get(tok, iColon), ":")) continue;
    if (tok_doubleFor_v2_debug) print("have colon");
    tok_typesAndNamesOfParams_keepModifiers.set(true);
    L<Pair<S>> args = tok_typesAndNamesOfParams(subList(tok, argsFrom-1, iColon-1));
    if (l(args) != 2) continue; // simple for or a three-argument for (out of this world!)
    
    // S a, b => S a, S b
    if (eq(second(args).a, "?")) second(args).a = first(args).a;
    
    if (tok_doubleFor_v2_debug) print("have 2 args: " + sfu(args));
    int iClosing = tok_findEndOfForExpression(tok, iColon+2);
    if (iClosing < 0) continue;
    if (tok_doubleFor_v2_debug) print("have closing");
    S exp = trimJoinSubList(tok, iColon+2, iClosing-1);
    if (tok_doubleFor_v2_debug) print("Expression: " + exp);
    int iCurly = iClosing+2;
    if (neq(get(tok, iCurly), "{")) fail("please use { with double for");
    int iCurlyEnd = findEndOfStatement(tok, iCurly)-1;
    if (iCurlyEnd < 0) continue;
    if (tok_doubleFor_v2_debug) print("have curly end");
    
    // complicated expression? evaluate to variable first
    
    if (!isIdentifier(exp)) {
      S expVar = makeVar();
      S mapType = tok_toNonPrimitiveTypes("Map<" + first(args).a + ", " + second(args).a + ">");
      tokPrepend(tok, i, "{ final " + mapType + " " + expVar + " = " + exp + "; ");
      tokAppend(tok, iCurlyEnd, "}");
      replaceTokens(tok, iColon+2, iClosing-1, expVar);
      exp = expVar;
    }
    
    tokAppend(tok, iColon, " keys(");
    tokPrepend(tok, iClosing, ")");
    
    replaceTokens(tok, argsFrom, iColon-1, joinPairWithSpace(first(args)));
    tokAppend(tok, iCurly, " " + joinPairWithSpace(second(args)) + " =" + exp + ".get(" + first(args).b + "); ");
    reTok(tok, i, iCurlyEnd+1);
  }
}

Began life as a copy of #1013206