Add test for yield* of iterator with throwing get:current

Change-Id: Idafa467a5e196d2351b3e5989177b39e959fddc5
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/294882
Reviewed-by: Lasse Nielsen <lrn@google.com>
Commit-Queue: Stephen Adams <sra@google.com>

tests/language/sync_star/sync_star_exception_current_test.dart

@@ -0,0 +1,53 @@
+// Copyright (c) 2023, 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.
+
+import 'dart:collection';
+import 'package:expect/expect.dart';
+
+class ThrowingCurrentIterator implements Iterator<int> {
+  int _remaining;
+  ThrowingCurrentIterator(this._remaining);
+
+  bool moveNext() => _remaining-- > 0;
+  int get current => throw 'current';
+}
+
+class ThrowingCurrent extends IterableBase<int> {
+  final int _length;
+  ThrowingCurrent(this._length);
+  Iterator<int> get iterator => ThrowingCurrentIterator(_length);
+}
+
+Iterable<int> f1() sync* {
+  yield* ThrowingCurrent(5);
+  yield* ThrowingCurrent(5);
+}
+
+Iterable<int> f2() sync* {
+  yield* f1();
+  yield* f1();
+}
+
+main() {
+  // `IterableBase.length` uses only `moveNext()`.
+  Expect.equals(5, ThrowingCurrent(5).length);
+
+  // The spec dictates that `yield*` calls `moveNext()` and `current` for each
+  // element in order to add the value to the iterable associated with the
+  // generator.
+  final i1 = f1().iterator;
+  Expect.throws(() => i1.moveNext());
+
+  // Further calls to `moveNext()` must return false (17.15).
+  Expect.isFalse(i1.moveNext());
+
+  // Same tests but for nested `yield*`.
+  final i2 = f2().iterator;
+  Expect.throws(() => i2.moveNext());
+  Expect.isFalse(i2.moveNext());
+
+  // Slighly surprising consequence of the specified behavior.
+  Expect.throws(() => f1().length);
+  Expect.throws(() => f2().length);
+}

tests/language_2/sync_star/sync_star_exception_current_test.dart

@@ -0,0 +1,55 @@
+// Copyright (c) 2023, 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.
+
+// @dart = 2.9
+
+import 'dart:collection';
+import 'package:expect/expect.dart';
+
+class ThrowingCurrentIterator implements Iterator<int> {
+  int _remaining;
+  ThrowingCurrentIterator(this._remaining);
+
+  bool moveNext() => _remaining-- > 0;
+  int get current => throw 'current';
+}
+
+class ThrowingCurrent extends IterableBase<int> {
+  final int _length;
+  ThrowingCurrent(this._length);
+  Iterator<int> get iterator => ThrowingCurrentIterator(_length);
+}
+
+Iterable<int> f1() sync* {
+  yield* ThrowingCurrent(5);
+  yield* ThrowingCurrent(5);
+}
+
+Iterable<int> f2() sync* {
+  yield* f1();
+  yield* f1();
+}
+
+main() {
+  // `IterableBase.length` uses only `moveNext()`.
+  Expect.equals(5, ThrowingCurrent(5).length);
+
+  // The spec dictates that `yield*` calls `moveNext()` and `current` for each
+  // element in order to add the value to the iterable associated with the
+  // generator.
+  final i1 = f1().iterator;
+  Expect.throws(() => i1.moveNext());
+
+  // Further calls to `moveNext()` must return false (17.15).
+  Expect.isFalse(i1.moveNext());
+
+  // Same tests but for nested `yield*`.
+  final i2 = f2().iterator;
+  Expect.throws(() => i2.moveNext());
+  Expect.isFalse(i2.moveNext());
+
+  // Slighly surprising consequence of the specified behavior.
+  Expect.throws(() => f1().length);
+  Expect.throws(() => f2().length);
+}