Add support for patching fields.

pkg/analyzer/lib/src/dart/sdk/patch.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.src.dart.sdk.patch;
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/token.dart';
 import 'package:analyzer/error/listener.dart';
 import 'package:analyzer/file_system/file_system.dart';
@@ skipping 82 matching lines @@
         'The patch file $_patchDesc for $_baseDesc $message at $loc.');
   }
 
   String _getLocationDesc3(CompilationUnit unit, int offset) {
     LineInfo_Location location = unit.lineInfo.getLocation(offset);
     return 'the line ${location.lineNumber}';
   }
 
   void _patchClassMembers(
       ClassDeclaration baseClass, ClassDeclaration patchClass) {
+    String className = baseClass.name.name;
     List<ClassMember> membersToAppend = [];
     for (ClassMember patchMember in patchClass.members) {
-      if (patchMember is MethodDeclaration) {
+      if (patchMember is FieldDeclaration) {
+        if (_hasPatchAnnotation(patchMember.metadata)) {
+          _failInPatch('attempts to patch a field', patchMember.offset);
+        }
+        List<VariableDeclaration> fields = patchMember.fields.variables;
+        if (fields.length != 1) {
+          _failInPatch('contains a field declaration with more than one field',
+              patchMember.offset);
+        }
+        String name = fields[0].name.name;
+        if (!Identifier.isPrivateName(className) &&
+            !Identifier.isPrivateName(name)) {
+          // TODO(scheglov) allow adding public fields into dart:_internal
+          _failInPatch('contains a public field', patchMember.offset);
+        }
+        membersToAppend.add(patchMember);
+      } else if (patchMember is MethodDeclaration) {
         String name = patchMember.name.name;
         if (_hasPatchAnnotation(patchMember.metadata)) {
           for (ClassMember baseMember in baseClass.members) {
             if (baseMember is MethodDeclaration &&
                 baseMember.name.name == name) {
               // Remove the "external" keyword.
               Token externalKeyword = baseMember.externalKeyword;
               if (externalKeyword != null) {
                 baseMember.externalKeyword = null;
                 _removeToken(externalKeyword);
@@ skipping 58 matching lines @@
                 patchBody.endToken.setNext(baseBody.endToken.next);
               } else {
                 _replaceNodeTokens(baseBody, patchBody);
               }
               // Replace the body.
               baseMember.body = patchBody;
             }
           }
         } else {
           if (name == null) {
-            if (!Identifier.isPrivateName(baseClass.name.name)) {
+            if (!Identifier.isPrivateName(className)) {
               _failInPatch(
                   'contains an unnamed public constructor', patchMember.offset);
             }
           } else {
             _failIfPublicName(patchMember, name);
           }
           membersToAppend.add(patchMember);
         }
       } else {
-        // TODO(scheglov) support field
         String className = patchClass.name.name;
         _failInPatch('contains an unsupported class member in $className',
             patchMember.offset);
       }
     }
     // Append new class members.
     _appendToNodeList(
         baseClass.members, membersToAppend, baseClass.leftBracket);
   }
 
@@ skipping 129 matching lines @@
   }
 
   /**
    * Replace tokens of the [oldNode] with tokens of the [newNode].
    */
   static void _replaceNodeTokens(AstNode oldNode, AstNode newNode) {
     oldNode.beginToken.previous.setNext(newNode.beginToken);
     newNode.endToken.setNext(oldNode.endToken.next);
   }
 }