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// 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 a class [C] in an opted-in library implements the same generic
/// class [I] more than once as [I0], .., [In], and at least one of the [Ii] is
/// not syntactically equal to the others, then it is an error if
/// [NNBD_TOP_MERGE(S0, ..., Sn)] is not defined where [Si] is [NORM(Ii)].
/// Otherwise, for the purposes of runtime subtyping checks, [C] is considered to
/// implement the canonical interface given by [NNBD_TOP_MERGE(S0, ..., Sn)].
/// @description Check that error occurs as a result of [NNBD_TOP_MERGE] of
/// [Object?] vs [void] and [Null].
/// @author
class A<T> {}
class B implements A<Object?> {}
class C implements A<Null > {}
class D extends B implements C {}
// ^
// [analyzer] unspecified
// [cfe] unspecified
class D1 extends C implements B {}
// ^^
// [analyzer] unspecified
// [cfe] unspecified
void main() {}