It is an error for an extension to declare an abstract method

Change-Id: I66f708dbe1f42b905b626b105a87c30325eb5c77
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/108900
Reviewed-by: Konstantin Shcheglov <[email protected]>
Reviewed-by: Phil Quitslund <[email protected]>
Commit-Queue: Brian Wilkerson <[email protected]>

Author: bwilkerson

pkg/analyzer/lib/error/error.dart

@@ -135,6 +135,7 @@ const List<ErrorCode> errorCodeValues = const [
   CompileTimeErrorCode.EXTENDS_DEFERRED_CLASS,
   CompileTimeErrorCode.EXTENDS_DISALLOWED_CLASS,
   CompileTimeErrorCode.EXTENDS_NON_CLASS,
+  CompileTimeErrorCode.EXTENSION_DECLARES_ABSTRACT_METHOD,
   CompileTimeErrorCode.EXTENSION_DECLARES_CONSTRUCTOR,
   CompileTimeErrorCode.EXTENSION_DECLARES_INSTANCE_FIELD,
   CompileTimeErrorCode.EXTRA_POSITIONAL_ARGUMENTS,

pkg/analyzer/lib/src/error/codes.dart

@@ -1174,6 +1174,14 @@ class CompileTimeErrorCode extends ErrorCode {
           correction: "Try specifying a different superclass, or "
               "removing the extends clause.");
 
+  /**
+   * No parameters.
+   */
+  static const CompileTimeErrorCode EXTENSION_DECLARES_ABSTRACT_METHOD =
+      const CompileTimeErrorCode('EXTENSION_DECLARES_ABSTRACT_METHOD',
+          "Extensions can't declare abstract methods.",
+          correction: "Try providing an implementation for the method.");
+
   /**
    * No parameters.
    */

pkg/analyzer/lib/src/fasta/ast_builder.dart

@@ -1571,6 +1571,11 @@ class AstBuilder extends StackListener {
             messageConstMethod, modifiers.constKeyword, modifiers.constKeyword);
       }
       checkFieldFormalParameters(parameters);
+      if (extensionDeclaration != null && body is EmptyFunctionBody) {
+        errorReporter.errorReporter.reportErrorForNode(
+            CompileTimeErrorCode.EXTENSION_DECLARES_ABSTRACT_METHOD, name);
+        return;
+      }
       currentDeclarationMembers.add(ast.methodDeclaration(
           comment,
           metadata,

pkg/analyzer/test/src/diagnostics/extension_declares_abstract_method_test.dart

@@ -0,0 +1,70 @@
+// Copyright (c) 2019, 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 'package:analyzer/dart/analysis/features.dart';
+import 'package:analyzer/src/error/codes.dart';
+import 'package:analyzer/src/generated/engine.dart';
+import 'package:test_reflective_loader/test_reflective_loader.dart';
+
+import '../dart/resolution/driver_resolution.dart';
+
+main() {
+  defineReflectiveSuite(() {
+    defineReflectiveTests(ExtensionDeclaresAbstractMethodTest);
+  });
+}
+
+@reflectiveTest
+class ExtensionDeclaresAbstractMethodTest extends DriverResolutionTest {
+  @override
+  AnalysisOptionsImpl get analysisOptions => AnalysisOptionsImpl()
+    ..contextFeatures = new FeatureSet.forTesting(
+        sdkVersion: '2.3.0', additionalFeatures: [Feature.extension_methods]);
+
+  test_getter() {
+    assertErrorsInCode('''
+extension E on String {
+  bool get isPalindrome;
+}
+''', [
+      error(CompileTimeErrorCode.EXTENSION_DECLARES_ABSTRACT_METHOD, 35, 12),
+    ]);
+  }
+
+  test_method() {
+    assertErrorsInCode('''
+extension E on String {
+  String reversed();
+}
+''', [
+      error(CompileTimeErrorCode.EXTENSION_DECLARES_ABSTRACT_METHOD, 33, 8),
+    ]);
+  }
+
+  test_none() {
+    assertNoErrorsInCode('''
+extension E on String {}
+''');
+  }
+
+  test_operator() {
+    assertErrorsInCode('''
+extension E on String {
+  String operator -(String otherString);
+}
+''', [
+      error(CompileTimeErrorCode.EXTENSION_DECLARES_ABSTRACT_METHOD, 42, 1),
+    ]);
+  }
+
+  test_setter() {
+    assertErrorsInCode('''
+extension E on String {
+  set length(int newLength);
+}
+''', [
+      error(CompileTimeErrorCode.EXTENSION_DECLARES_ABSTRACT_METHOD, 30, 6),
+    ]);
+  }
+}

pkg/analyzer/test/src/diagnostics/test_all.dart

@@ -40,6 +40,8 @@ import 'equal_elements_in_const_set_test.dart' as equal_elements_in_const_set;
 import 'equal_keys_in_const_map_test.dart' as equal_keys_in_const_map;
 import 'expression_in_map_test.dart' as expression_in_map;
 import 'extends_non_class_test.dart' as extends_non_class;
+import 'extension_declares_abstract_method_test.dart'
+    as extension_declares_abstract_method;
 import 'extension_declares_constructor_test.dart'
     as extension_declares_constructor;
 import 'extension_declares_field_test.dart' as extension_declares_field;
@@ -223,6 +225,7 @@ main() {
     equal_keys_in_const_map.main();
     expression_in_map.main();
     extends_non_class.main();
+    extension_declares_abstract_method.main();
     extension_declares_constructor.main();
     extension_declares_field.main();
     final_not_initialized.main();