Setup correct scope for initializers and complain about fields initialized more than once.

pkg/front_end/lib/src/fasta/kernel/kernel_field_builder.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 fasta.kernel_field_builder;
 
 import 'package:front_end/src/fasta/kernel/body_builder.dart' show BodyBuilder;
 
 import 'package:front_end/src/fasta/kernel/kernel_shadow_ast.dart'
     show KernelField;
 
 import 'package:front_end/src/fasta/parser/parser.dart' show Parser;
 
 import 'package:front_end/src/scanner/token.dart' show Token;
 
 import 'package:front_end/src/fasta/builder/class_builder.dart'
     show ClassBuilder;
 
 import 'package:front_end/src/fasta/source/source_library_builder.dart'
     show SourceLibraryBuilder;
 
 import 'package:front_end/src/fasta/type_inference/type_inference_listener.dart'
     show TypeInferenceListener;
 
-import 'package:kernel/ast.dart' show DartType, Expression, Field, Name;
+import 'package:kernel/ast.dart'
+    show DartType, Expression, Field, Name, NullLiteral;
+
+import '../errors.dart' show internalError;
 
 import 'kernel_builder.dart'
     show Builder, FieldBuilder, KernelTypeBuilder, MetadataBuilder;
 
 class KernelFieldBuilder extends FieldBuilder<Expression> {
   final Field field;
   final List<MetadataBuilder> metadata;
   final KernelTypeBuilder type;
   final Token initializerToken;
 
   KernelFieldBuilder(this.metadata, this.type, String name, int modifiers,
       Builder compilationUnit, int charOffset, this.initializerToken)
       : field = new KernelField(null, fileUri: compilationUnit?.relativeFileUri)
           ..fileOffset = charOffset,
         super(name, modifiers, compilationUnit, charOffset);
 
+  bool get hasInitializer => initializerToken != null;
+
   void set initializer(Expression value) {
+    if (!hasInitializer && value is! NullLiteral && !isConst && !isFinal) {
+      internalError("Attempt to set initializer on field without initializer.");
+    }
     field.initializer = value..parent = field;
   }
 
   Field build(SourceLibraryBuilder library) {
     field.name ??= new Name(name, library.target);
     if (type != null) {
       field.type = type.build(library);
     }
     bool isInstanceMember = !isStatic && !isTopLevel;
     field
       ..isFinal = isFinal
       ..isConst = isConst
       ..hasImplicitGetter = isInstanceMember
       ..hasImplicitSetter = isInstanceMember && !isConst && !isFinal
       ..isStatic = !isInstanceMember;
-    if (initializerToken != null) {
+    if (initializerToken != null && !initializerToken.isEof) {
       library.loader.typeInferenceEngine.recordField(field);
     }
     return field;
   }
 
   Field get target => field;
 
   @override
   void prepareInitializerInference(
       SourceLibraryBuilder library, ClassBuilder currentClass) {
-    if (initializerToken != null) {
+    if (initializerToken != null && !initializerToken.isEof) {
       var memberScope =
           currentClass == null ? library.scope : currentClass.scope;
       // TODO(paulberry): Is it correct to pass library.uri into BodyBuilder, or
       // should it be the part URI?
       var typeInferenceEngine = library.loader.typeInferenceEngine;
       var listener = new TypeInferenceListener();
       var typeInferrer =
           typeInferenceEngine.createTopLevelTypeInferrer(field, listener);
       var bodyBuilder = new BodyBuilder(
           library,
@@ skipping 10 matching lines @@
       Token token = parser.parseExpression(initializerToken);
       Expression expression = bodyBuilder.popForValue();
       bodyBuilder.checkEmpty(token.charOffset);
       initializer = expression;
     }
   }
 
   @override
   DartType get builtType => field.type;
 }