[cfe] Add test for extension on Never

Closes #42180

Change-Id: I690d3419d94bfc593f77f0cea75274cb20182ba2
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/151229
Reviewed-by: Dmitry Stefantsov <dmitryas@google.com>
Commit-Queue: Johnni Winther <johnniwinther@google.com>

pkg/front_end/testcases/nnbd/extension_never.dart

@@ -0,0 +1,18 @@
+// 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.
+
+extension Extension on Never {
+  extensionMethod() {}
+}
+
+implicitAccess(Never never) {
+  never.extensionMethod();
+  never.missingMethod();
+}
+
+explicitAccess(Never never) {
+  Extension(never).extensionMethod();
+}
+
+main() {}

pkg/front_end/testcases/nnbd/extension_never.dart.outline.expect

@@ -0,0 +1,17 @@
+library /*isNonNullableByDefault*/;
+import self as self;
+
+extension Extension on Never {
+  method extensionMethod = self::Extension|extensionMethod;
+  tearoff extensionMethod = self::Extension|get#extensionMethod;
+}
+static method Extension|extensionMethod(final Never #this) → dynamic
+  ;
+static method Extension|get#extensionMethod(final Never #this) → () → dynamic
+  return () → dynamic => self::Extension|extensionMethod(#this);
+static method implicitAccess(Never never) → dynamic
+  ;
+static method explicitAccess(Never never) → dynamic
+  ;
+static method main() → dynamic
+  ;

pkg/front_end/testcases/nnbd/extension_never.dart.strong.expect

@@ -0,0 +1,18 @@
+library /*isNonNullableByDefault*/;
+import self as self;
+
+extension Extension on Never {
+  method extensionMethod = self::Extension|extensionMethod;
+  tearoff extensionMethod = self::Extension|get#extensionMethod;
+}
+static method Extension|extensionMethod(final Never #this) → dynamic {}
+static method Extension|get#extensionMethod(final Never #this) → () → dynamic
+  return () → dynamic => self::Extension|extensionMethod(#this);
+static method implicitAccess(Never never) → dynamic {
+  never.extensionMethod();
+  never.missingMethod();
+}
+static method explicitAccess(Never never) → dynamic {
+  self::Extension|extensionMethod(never);
+}
+static method main() → dynamic {}

pkg/front_end/testcases/nnbd/extension_never.dart.strong.transformed.expect

@@ -0,0 +1,18 @@
+library /*isNonNullableByDefault*/;
+import self as self;
+
+extension Extension on Never {
+  method extensionMethod = self::Extension|extensionMethod;
+  tearoff extensionMethod = self::Extension|get#extensionMethod;
+}
+static method Extension|extensionMethod(final Never #this) → dynamic {}
+static method Extension|get#extensionMethod(final Never #this) → () → dynamic
+  return () → dynamic => self::Extension|extensionMethod(#this);
+static method implicitAccess(Never never) → dynamic {
+  never.extensionMethod();
+  never.missingMethod();
+}
+static method explicitAccess(Never never) → dynamic {
+  self::Extension|extensionMethod(never);
+}
+static method main() → dynamic {}

pkg/front_end/testcases/nnbd/extension_never.dart.textual_outline.expect

@@ -0,0 +1,5 @@
+extension Extension ;
+on Never (){ }
+implicitAccess(Never never) { }
+explicitAccess(Never never) { }
+main() { }

pkg/front_end/testcases/nnbd/extension_never.dart.weak.expect

@@ -0,0 +1,18 @@
+library /*isNonNullableByDefault*/;
+import self as self;
+
+extension Extension on Never {
+  method extensionMethod = self::Extension|extensionMethod;
+  tearoff extensionMethod = self::Extension|get#extensionMethod;
+}
+static method Extension|extensionMethod(final Never #this) → dynamic {}
+static method Extension|get#extensionMethod(final Never #this) → () → dynamic
+  return () → dynamic => self::Extension|extensionMethod(#this);
+static method implicitAccess(Never never) → dynamic {
+  never.extensionMethod();
+  never.missingMethod();
+}
+static method explicitAccess(Never never) → dynamic {
+  self::Extension|extensionMethod(never);
+}
+static method main() → dynamic {}

pkg/front_end/testcases/nnbd/extension_never.dart.weak.transformed.expect

@@ -0,0 +1,18 @@
+library /*isNonNullableByDefault*/;
+import self as self;
+
+extension Extension on Never {
+  method extensionMethod = self::Extension|extensionMethod;
+  tearoff extensionMethod = self::Extension|get#extensionMethod;
+}
+static method Extension|extensionMethod(final Never #this) → dynamic {}
+static method Extension|get#extensionMethod(final Never #this) → () → dynamic
+  return () → dynamic => self::Extension|extensionMethod(#this);
+static method implicitAccess(Never never) → dynamic {
+  never.extensionMethod();
+  never.missingMethod();
+}
+static method explicitAccess(Never never) → dynamic {
+  self::Extension|extensionMethod(never);
+}
+static method main() → dynamic {}

pkg/front_end/testcases/textual_outline.status

@@ -156,6 +156,7 @@ late_lowering/override_getter_setter: FormatterCrash
 late_lowering/override: FormatterCrash
 late_lowering/uninitialized_non_nullable_late_fields: FormatterCrash
 nnbd/covariant_late_field: FormatterCrash
+nnbd/extension_never: FormatterCrash
 nnbd/forbidden_supers: FormatterCrash
 nnbd/infer_if_null: FormatterCrash
 nnbd/inheritance_from_opt_in: FormatterCrash