Rework type inference of assignments to index expressions.

pkg/front_end/lib/src/fasta/kernel/fasta_accessors.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.fasta_accessors;
 
 import 'package:front_end/src/fasta/kernel/kernel_shadow_ast.dart'
-    show KernelArguments, KernelThisExpression;
+    show KernelArguments, KernelComplexAssignment, KernelThisExpression;
 
 import 'package:front_end/src/fasta/kernel/utils.dart' show offsetForToken;
 
 import 'package:front_end/src/scanner/token.dart' show Token;
 
 import 'frontend_accessors.dart' show Accessor;
 
 import 'package:front_end/src/fasta/type_inference/type_promotion.dart'
     show TypePromoter;
 
@@ skipping 164 matching lines @@
       int offset}) {
     return helper.throwNoSuchMethodError(receiver, name ?? plainNameForWrite,
         arguments, offset ?? offsetForToken(this.token),
         isGetter: isGetter,
         isSetter: isSetter,
         isSuper: isSuper,
         isStatic: isStatic);
   }
 
   bool get isThisPropertyAccessor => false;
+
+  @override
+  KernelComplexAssignment startComplexAssignment(Expression rhs) => null;
 }
 
 abstract class ErrorAccessor implements FastaAccessor {
   /// Pass [arguments] that must be evaluated before throwing an error.  At
   /// most one of [isGetter] and [isSetter] should be true and they're passed
   /// to [BuilderHelper.buildThrowNoSuchMethodError] if it is used.
   Expression buildError(Arguments arguments,
       {bool isGetter: false, bool isSetter: false, int offset});
 
   Name get name => internalError("Unsupported operation.");
@@ skipping 391 matching lines @@
       Expression index,
       Procedure getter,
       Procedure setter) {
     if (receiver is ThisExpression) {
       return new ThisIndexAccessor(helper, token, index, getter, setter);
     } else {
       return new IndexAccessor.internal(
           helper, token, receiver, index, getter, setter);
     }
   }
+
+  @override
+  KernelComplexAssignment startComplexAssignment(Expression rhs) =>
+      new KernelComplexAssignment()
+        ..receiver = receiver
+        ..index = index
+        ..rhs = rhs;
 }
 
 class PropertyAccessor extends kernel.PropertyAccessor with FastaAccessor {
   final BuilderHelper helper;
 
   PropertyAccessor.internal(this.helper, Token token, Expression receiver,
       Name name, Member getter, Member setter)
       : super.internal(helper, receiver, name, getter, setter, token);
 
   String get plainNameForRead => name.name;
@@ skipping 357 matching lines @@
     offset ??= offsetForToken(this.token);
     return helper.throwNoSuchMethodError(new NullLiteral()..fileOffset = offset,
         plainNameForRead, arguments, offset,
         isGetter: isGetter, isSetter: isSetter);
   }
 }
 
 bool isFieldOrGetter(Member member) {
   return member is Field || (member is Procedure && member.isGetter);
 }