LanguageFeatures/nnbd/flow-analysis/reachability_A07_t06.dart

// Copyright (c) 2020, 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 N is an expression of the form E1.m1(E2), then:
 *
 *  Let before(E1) = before(N)
 *  Let before(E2) = after(E2)
 *  Let T be the static return type of the invocation
 *  If T <: Never then:
 *    Let null(N) = unreachable(before(N)).
 *    Let notNull(N) = unreachable(before(N)).
 *  Otherwise if T <: Null then:
 *    Let null(N) = before(N).
 *    Let notNull(N) = unreachable(before(N)).
 *  Otherwise if T is non-nullable then:
 *    Let null(N) = before(N).
 *    Let notNull(N) = unreachable(before(N)).
 *  Otherwise:
 *    Let null(N) = promote(x, Null, before(N))
 *    Let notNull(N) = promoteToNonNull(x, before(N))
 *
 * @description Checks reachability after method call. Test static method and
 * return type T <: Null
 *
 * @author sgrekhov@unipro.ru
 * @issue 41985
 */
// Requirements=nnbd-strong

class C {
  static Null m1() => null;
}

main() {
  int i;
  if (C.m1() == null) {
    i = 42;   // condition is always true therefore `i` must be definitely assigned
  }
  i; // It's not an error to read local non-nullable variable if it is definitely assigned
}