Improve handling of complicated getters and setters.

pkg/front_end/lib/src/fasta/builder/class_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.class_builder;
 
 import '../errors.dart' show internalError;
 
 import 'builder.dart'
     show
         Builder,
         ConstructorReferenceBuilder,
         LibraryBuilder,
         MetadataBuilder,
         MixinApplicationBuilder,
         NamedTypeBuilder,
         TypeBuilder,
         TypeDeclarationBuilder,
         TypeVariableBuilder;
 
-import 'scope.dart' show AmbiguousBuilder, Scope;
+import 'scope.dart' show AccessErrorBuilder, AmbiguousBuilder, Scope;
 
 abstract class ClassBuilder<T extends TypeBuilder, R>
     extends TypeDeclarationBuilder<T, R> {
   final List<TypeVariableBuilder> typeVariables;
 
   T supertype;
 
   List<T> interfaces;
 
   final Map<String, Builder> members;
@@ skipping 58 matching lines @@
       while (current != null) {
         if (current.isGetter && getterBuilder == null) {
           getterBuilder = current;
         } else if (current.isSetter && setterBuilder == null) {
           setterBuilder = current;
         } else {
           return new AmbiguousBuilder(name, builder, charOffset, fileUri);
         }
         current = current.next;
       }
+      if (getterBuilder?.isInstanceMember ?? false) {
+        getterBuilder = null;
+      }
+      if (setterBuilder?.isInstanceMember ?? false) {
+        setterBuilder = null;
+      }
       builder = isSetter ? setterBuilder : getterBuilder;
+      if (builder == null) {
+        if (isSetter && getterBuilder != null) {
+          return new AccessErrorBuilder(
+              name, getterBuilder, charOffset, fileUri);
+        } else if (!isSetter && setterBuilder != null) {
+          return new AccessErrorBuilder(
+              name, setterBuilder, charOffset, fileUri);
+        }
+      }
     }
     if (builder == null) {
       return null;
     } else if (isSetter && builder.isGetter) {
       return null;
     } else {
       return builder.isInstanceMember ? null : builder;
     }
   }
 
@@ skipping 55 matching lines @@
             argument = argument.subst(substitutionMap);
           }
           directSubstitutionMap[variables[i]] = argument;
         }
         substitutionMap = directSubstitutionMap;
       }
     }
     return substitutionMap;
   }
 }