Add error checking for the immutable annotation (issue 27750)

pkg/analyzer/test/generated/hint_code_test.dart

 // Copyright (c) 2016, 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.
 
 library analyzer.test.generated.hint_code_test;
 
 import 'package:analyzer/error/error.dart';
 import 'package:analyzer/src/error/codes.dart';
 import 'package:analyzer/src/generated/engine.dart';
 import 'package:analyzer/src/generated/parser.dart';
@@ skipping 13 matching lines @@
 class HintCodeTest extends ResolverTestCase {
   @override
   void reset() {
     super.resetWith(packages: [
       [
         'meta',
         r'''
 library meta;
 
 const _Factory factory = const _Factory();
+const Immutable immutable = const Immutable();
 const _Literal literal = const _Literal();
 const _MustCallSuper mustCallSuper = const _MustCallSuper();
 const _Protected protected = const _Protected();
 const Required required = const Required();
 class Required {
   final String reason;
   const Required([this.reason]);
 }
 
+class Immutable {
+  final String reason;
+  const Immutable([this.reason]);
+}
 class _Factory {
   const _Factory();
 }
 class _Literal {
   const _Literal();
 }
 class _MustCallSuper {
   const _MustCallSuper();
 }
 class _Protected {
@@ skipping 1302 matching lines @@
 main() {
   var p1 = new Point(0, 0);
   var p2 = new Point(10, 10);
   int n = p1 + p2;
 }''');
     await computeAnalysisResult(source);
     assertErrors(source, [HintCode.INVALID_ASSIGNMENT]);
     verify([source]);
   }
 
+  test_invalidImmutableAnnotation_method() async {
+    Source source = addSource(r'''
+import 'package:meta/meta.dart';
+class A {
+  @immutable
+  void m() {}
+}
+''');
+    await computeAnalysisResult(source);
+    assertErrors(source, [HintCode.INVALID_IMMUTABLE_ANNOTATION]);
+    verify([source]);
+  }
+
   test_invalidUseOfProtectedMember_closure() async {
     Source source = addNamedSource(
         '/lib1.dart',
         r'''
 import 'package:meta/meta.dart';
 
 class A {
   @protected
   int a() => 42;
 }
@@ skipping 593 matching lines @@
   test_missingReturn_method() async {
     Source source = addSource(r'''
 class A {
   int m() {}
 }''');
     await computeAnalysisResult(source);
     assertErrors(source, [HintCode.MISSING_RETURN]);
     verify([source]);
   }
 
+  test_mustBeImmutable_direct() async {
+    Source source = addSource(r'''
+import 'package:meta/meta.dart';
+@immutable
+class A {
+  int x;
+}
+''');
+    await computeAnalysisResult(source);
+    assertErrors(source, [HintCode.MUST_BE_IMMUTABLE]);
+    verify([source]);
+  }
+
+  test_mustBeImmutable_extends() async {
+    Source source = addSource(r'''
+import 'package:meta/meta.dart';
+@immutable
+class A {}
+class B extends A {
+  int x;
+}
+''');
+    await computeAnalysisResult(source);
+    assertErrors(source, [HintCode.MUST_BE_IMMUTABLE]);
+    verify([source]);
+  }
+
+  test_mustBeImmutable_fromMixin() async {
+    Source source = addSource(r'''
+import 'package:meta/meta.dart';
+@immutable
+class A {}
+class B {
+  int x;
+}
+class C extends A with B {}
+''');
+    await computeAnalysisResult(source);
+    assertErrors(source, [HintCode.MUST_BE_IMMUTABLE]);
+    verify([source]);
+  }
+
   test_mustCallSuper() async {
     Source source = addSource(r'''
 import 'package:meta/meta.dart';
 class A {
   @mustCallSuper
   void a() {}
 }
 class B extends A {
   @override
   void a()
@@ skipping 2104 matching lines @@
   n() {
     var a = m(), b = m();
   }
 }''');
     await computeAnalysisResult(source);
     assertErrors(
         source, [HintCode.USE_OF_VOID_RESULT, HintCode.USE_OF_VOID_RESULT]);
     verify([source]);
   }
 }