Add support for patching fields.

pkg/analyzer/test/src/dart/sdk/patch_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.
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/token.dart';
 import 'package:analyzer/file_system/file_system.dart';
 import 'package:analyzer/file_system/memory_file_system.dart';
 import 'package:analyzer/src/dart/sdk/patch.dart';
 import 'package:analyzer/src/dart/sdk/sdk.dart';
@@ skipping 208 matching lines @@
 ''');
     _assertUnitCode(unit, 'class C {int f; C.named() : f = 2 {print(42);}}');
     ClassDeclaration clazz = unit.declarations[0];
     ConstructorDeclaration constructor = clazz.members[1];
     expect(constructor.externalKeyword, isNull);
     _assertPrevNextToken(constructor.parameters.endToken,
         constructor.initializers.beginToken.previous);
     _assertPrevNextToken(constructor.endToken, clazz.rightBracket);
   }
 
+  test_class_field_append() {
+    CompilationUnit unit = _doTopLevelPatching(
+        r'''
+class C {
+  void a() {}
+}
+''',
+        r'''
+@patch
+class C {
+  int _b = 42;
+}
+''');
+    _assertUnitCode(unit, 'class C {void a() {} int _b = 42;}');
+    ClassDeclaration clazz = unit.declarations[0];
+    MethodDeclaration a = clazz.members[0];
+    FieldDeclaration b = clazz.members[1];
+    _assertPrevNextToken(a.endToken, b.beginToken);
+    _assertPrevNextToken(b.endToken, clazz.rightBracket);
+  }
+
+  test_class_field_append_fail_moreThanOne() {
+    expect(() {
+      _doTopLevelPatching(
+          r'''
+class A {}
+''',
+          r'''
+@patch
+class A {
+  @patch
+  int _f1, _f2;
+}
+''');
+    }, throwsArgumentError);
+  }
+
+  test_class_field_append_fail_notPrivate() {
+    expect(() {
+      _doTopLevelPatching(
+          r'''
+class A {}
+''',
+          r'''
+@patch
+class A {
+  @patch
+  int b;
+}
+''');
+    }, throwsArgumentError);
+  }
+
+  test_class_field_append_publiInPrivateClass() {
+    CompilationUnit unit = _doTopLevelPatching(
+        r'''
+class _C {
+  void a() {}
+}
+''',
+        r'''
+@patch
+class _C {
+  int b = 42;
+}
+''');
+    _assertUnitCode(unit, 'class _C {void a() {} int b = 42;}');
+    ClassDeclaration clazz = unit.declarations[0];
+    MethodDeclaration a = clazz.members[0];
+    FieldDeclaration b = clazz.members[1];
+    _assertPrevNextToken(a.endToken, b.beginToken);
+    _assertPrevNextToken(b.endToken, clazz.rightBracket);
+  }
+
+  test_class_field_patch_fail() {
+    expect(() {
+      _doTopLevelPatching(
+          r'''
+class A {}
+''',
+          r'''
+@patch
+class A {
+  @patch
+  int _f;
+}
+''');
+    }, throwsArgumentError);
+  }
+
   test_class_getter_append() {
     CompilationUnit unit = _doTopLevelPatching(
         r'''
 class C {
   void a() {}
 }
 ''',
         r'''
 @patch
 class C {
@@ skipping 399 matching lines @@
   void _setSdkLibraries(String code) {
     provider.newFile(
         _p('/sdk/lib/_internal/sdk_library_metadata/lib/libraries.dart'), code);
   }
 
   static void _assertPrevNextToken(Token prev, Token next) {
     expect(prev.next, same(next));
     expect(next.previous, same(prev));
   }
 }