#1400. Add extension types tests for bottom types (#2944)

LanguageFeatures/Extension-types/static_analysis_extension_types_A34_t01.dart

@@ -0,0 +1,27 @@
+// Copyright (c) 2024, 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 A compile-time error occurs if the representation type of an
+/// extension type declaration is a bottom type.
+///
+/// @description Check that it is a compile-time error if the representation
+/// type of an extension type declaration is a bottom type.
+/// @author [email protected]
+
+typedef NeverAlias = Never;
+
+extension type ET1(Never _) {}
+//                 ^^^^^
+// [analyzer] unspecified
+// [cfe] unspecified
+
+extension type ET2(NeverAlias _) {}
+//                 ^^^^^^^^^^
+// [analyzer] unspecified
+// [cfe] unspecified
+
+main() {
+  print(ET1);
+  print(ET2);
+}

LanguageFeatures/Extension-types/static_analysis_extension_types_A34_t02.dart

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+// Copyright (c) 2024, 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 Note that it is still possible for the instantiated
+/// representation type of a given extension type to be a bottom type. For
+/// example, assuming extension type `E<X>(X x) {}, E<Never>` would be an
+/// extension type whose instantiated representation type is `Never`.
+///
+/// @description Check that it is not an error to have an instantiated
+/// representation type to be a bottom type.
+/// @author [email protected]
+
+import '../../Utils/static_type_helper.dart';
+
+typedef NeverAlias = Never;
+
+extension type ET<X>(X _) {}
+
+main() {
+  ET<Never>? et1;
+  et1.expectStaticType<Exactly<ET<Never>?>>();
+  ET<NeverAlias>? et2;
+  et2.expectStaticType<Exactly<ET<Never>?>>();
+}