LanguageFeatures/nnbd/null_aware_operator_A13_t13.dart

// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

/// @assertion If e1 translates to F then e1?[e2] = e3 translates to:
///  SHORT[EXP(e1), fn[x] => x[EXP(e2)] = EXP(e3)]
///
///  The other assignment operators are handled equivalently.
///
/// @description Check that assignments like e1?[e2] ??= e3 translates to:
///  SHORT[EXP(e1), fn[x] => x[EXP(e2)] ??= EXP(e3)]
/// @author sgrekhov@unipro.ru
/// @issue 40369
/// @issue 40557

import "../../Utils/expect.dart";

class C {
  List<int>? _list = [3, 1, 4];
  int operator [](int index) {
    List<int>? list = _list;
    if (list != null) {
      return list[index];
    }
    return -1;
  }
  void operator []=(int index, dynamic value) {
    List<int>? list = _list;
    if (list != null) {
      list[index] = value;
    }
  }

  void init() {
    _list = [3, 1, 4];
  }
}

void testShort(C? x, int index, dynamic value) {
  var actual = x?[index] ??= value;
//                           ^^^^^
// [analyzer] STATIC_WARNING.DEAD_NULL_AWARE_EXPRESSION
  var n0 = x;
  x?.init();
  var expected = n0 == null ? null : n0[index] ??= value;
//                                                 ^^^^^
// [analyzer] STATIC_WARNING.DEAD_NULL_AWARE_EXPRESSION
  Expect.equals(expected, actual);
}

main() {
  C? c1 = null;
  testShort(c1, 0, 7);
  c1 = new C();
  testShort(c1, 0, 7);

  C c2 = new C();
  testShort(c2, 0, 7);
}