dart-lang#2139. Add generator functions element type tests

Language/Functions/element_type_A01_t01.dart

@@ -0,0 +1,56 @@
+// 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.
+
+/// @assertion We define the union-free type of a type `T` as follows:
+/// If `T` is of the form `S?` or the form `FutureOr<S>` then the union-free
+/// type of `T` is the union-free type of `S`. Otherwise, the union-free type
+/// of `T` is T.
+///
+/// We define the element type of a generator function `f` as follows:
+/// Let `S` be the union-free type of the declared return type of `f`. If `f` is
+/// a synchronous generator and `S` implements `Iterable<U>` for some `U` then
+/// the element type of `f` is `U`.
+///
+/// @description Check that element type of a synchronous generator function `f`
+/// is `U`, where `S` is a union-free type of the declared return type of `f`
+/// and `S` implements `Iterable<U>`
+/// @author [email protected]
+
+import "dart:async";
+
+Iterable<num?>? f1() sync* {
+  yield 1;
+  yield 3.14;
+  yield null; // Ok, element type is `num?`
+}
+
+Iterable<num>? f2() sync* {
+  yield 1;
+  yield null;
+//      ^^^^
+// [analyzer] unspecified
+// [cfe] unspecified
+}
+
+FutureOr<Iterable<num>?> f3() sync* {
+  yield 1;
+  yield null;
+//      ^^^^
+// [analyzer] unspecified
+// [cfe] unspecified
+  yield Future<Null>.value(null);
+//      ^^^^^^^^^^^^^^^^^^^^^^^^
+// [analyzer] unspecified
+// [cfe] unspecified
+  yield Future<num>.value(1);
+//      ^^^^^^^^^^^^^^^^^^^^
+// [analyzer] unspecified
+// [cfe] unspecified
+}
+
+main() {
+  f1();
+  f2();
+  f3();
+}

Language/Functions/element_type_A02_t01.dart

@@ -0,0 +1,57 @@
+// 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.
+
+/// @assertion We define the union-free type of a type `T` as follows:
+/// If `T` is of the form `S?` or the form `FutureOr<S>` then the union-free
+/// type of `T` is the union-free type of `S`. Otherwise, the union-free type
+/// of `T` is T.
+///
+/// We define the element type of a generator function `f` as follows:
+/// Let `S` be the union-free type of the declared return type of `f`.
+/// ...
+/// If `f` is an asynchronous generator and `S` implements `Stream<U>` for some
+/// `U` then the element type of `f` is `U`.
+///
+/// @description Check that element type of an asynchronous generator function
+/// `f` is `U`, where `S` is a union-free type of the declared return type of
+/// `f` and `S` implements `Stream<U>`
+/// @author [email protected]
+
+import "dart:async";
+
+Stream<num?>? f1() async* {
+  yield 1;
+  yield 3.14;
+  yield null; // Ok, element type is `num?`
+}
+
+Stream<num>? f2() async* {
+  yield 1;
+  yield null;
+//      ^^^^
+// [analyzer] unspecified
+// [cfe] unspecified
+}
+
+FutureOr<Stream<num>?> f3() async* {
+  yield 1;
+  yield null;
+//      ^^^^
+// [analyzer] unspecified
+// [cfe] unspecified
+  yield Future<Null>.value(null);
+//      ^^^^^^^^^^^^^^^^^^^^^^^^
+// [analyzer] unspecified
+// [cfe] unspecified
+  yield Future<num>.value(1);
+//      ^^^^^^^^^^^^^^^^^^^^
+// [analyzer] unspecified
+// [cfe] unspecified
+}
+
+main() {
+  f1();
+  f2();
+  f3();
+}

Language/Functions/element_type_A03_t01.dart

@@ -0,0 +1,54 @@
+// 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.
+
+/// @assertion We define the union-free type of a type `T` as follows:
+/// If `T` is of the form `S?` or the form `FutureOr<S>` then the union-free
+/// type of `T` is the union-free type of `S`. Otherwise, the union-free type
+/// of `T` is T.
+///
+/// We define the element type of a generator function `f` as follows:
+/// Let `S` be the union-free type of the declared return type of `f`.
+/// ...
+/// Otherwise, if `f` is a generator (synchronous or asynchronous) and `S` is a
+/// supertype of `Object` then the element type of `f` is dynamic
+///
+/// @description Check that element type of a synchronous generator function `f`
+/// is `dynamic`, if `S` is a union-free type of the declared return type of `f`
+/// and `S` is a supertype of `Object`
+/// @author [email protected]
+
+import "dart:async";
+
+Object? f1() sync* {
+  yield 1;
+  yield 3.14;
+  yield null;
+  yield "42";
+}
+
+Object f2() sync* {
+  yield 1;
+  yield null;
+}
+
+FutureOr<Object> f3() sync* {
+  yield 1;
+  yield null;
+  yield Future<Null>.value(null);
+  yield Future<num>.value(1);
+}
+
+FutureOr<Object?>? f4() sync* {
+  yield 1;
+  yield null;
+  yield Future<Null>.value(null);
+  yield Future<num>.value(1);
+}
+
+main() {
+  f1();
+  f2();
+  f3();
+  f4();
+}

Language/Functions/element_type_A03_t02.dart

@@ -0,0 +1,54 @@
+// 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.
+
+/// @assertion We define the union-free type of a type `T` as follows:
+/// If `T` is of the form `S?` or the form `FutureOr<S>` then the union-free
+/// type of `T` is the union-free type of `S`. Otherwise, the union-free type
+/// of `T` is T.
+///
+/// We define the element type of a generator function `f` as follows:
+/// Let `S` be the union-free type of the declared return type of `f`.
+/// ...
+/// Otherwise, if `f` is a generator (synchronous or asynchronous) and `S` is a
+/// supertype of Object then the element type of `f` is dynamic
+///
+/// @description Check that element type of an asynchronous generator function
+/// `f` is `dynamic`, if `S` is a union-free type of the declared return type of
+/// `f` and `S` is a supertype of `Object`
+/// @author [email protected]
+
+import "dart:async";
+
+Object? f1() sync* {
+  yield 1;
+  yield 3.14;
+  yield null;
+  yield "42";
+}
+
+Object f2() sync* {
+  yield 1;
+  yield null;
+}
+
+FutureOr<Object> f3() sync* {
+  yield 1;
+  yield null;
+  yield Future<Null>.value(null);
+  yield Future<num>.value(1);
+}
+
+FutureOr<Object?>? f4() sync* {
+  yield 1;
+  yield null;
+  yield Future<Null>.value(null);
+  yield Future<num>.value(1);
+}
+
+main() {
+  f1();
+  f2();
+  f3();
+  f4();
+}