Implement fullNameForErrors on all Builders.

pkg/front_end/lib/src/fasta/builder/scope.dart

Index: pkg/front_end/lib/src/fasta/builder/scope.dart
diff --git a/pkg/front_end/lib/src/fasta/builder/scope.dart b/pkg/front_end/lib/src/fasta/builder/scope.dart
index 60e4f9df796c23a62401fa05c64f9f64ca8276a1..2fe432982ec4967adb96df71a4679cf0306fe0a4 100644
--- a/pkg/front_end/lib/src/fasta/builder/scope.dart
+++ b/pkg/front_end/lib/src/fasta/builder/scope.dart
@@ -37,7 +37,7 @@ class Scope {
         return lookupAmbiguous(name, builder, false, charOffset, fileUri);
       }
       return builder.isSetter
-          ? new AccessErrorBuilder(builder, charOffset, fileUri)
+          ? new AccessErrorBuilder(name, builder, charOffset, fileUri)
           : builder;
     } else {
       return parent?.lookup(name, charOffset, fileUri);
@@ -52,14 +52,14 @@ class Scope {
       }
       if (builder.isField) {
         if (builder.isFinal) {
-          return new AccessErrorBuilder(builder, charOffset, fileUri);
+          return new AccessErrorBuilder(name, builder, charOffset, fileUri);
         } else {
           return builder;
         }
       } else if (builder.isSetter) {
         return builder;
       } else {
-        return new AccessErrorBuilder(builder, charOffset, fileUri);
+        return new AccessErrorBuilder(name, builder, charOffset, fileUri);
       }
     } else {
       return parent?.lookupSetter(name, charOffset, fileUri);
@@ -81,7 +81,7 @@ class Scope {
       } else if (current.isSetter && setterBuilder == null) {
         setterBuilder = current;
       } else {
-        return new AmbiguousBuilder(builder, charOffset, fileUri);
+        return new AmbiguousBuilder(name, builder, charOffset, fileUri);
       }
       current = current.next;
     }
@@ -133,16 +133,32 @@ class Scope {
   }
 }
 
-class AccessErrorBuilder extends Builder {
+abstract class ProblemBuilder extends Builder {
+  final String name;
+
   final Builder builder;
 
-  AccessErrorBuilder(this.builder, int charOffset, Uri fileUri)
+  ProblemBuilder(this.name, this.builder, int charOffset, Uri fileUri)
       : super(null, charOffset, fileUri);
 
-  Builder get parent => builder;
-
   get target => null;
 
+  bool get hasProblem => true;
+
+  String get message;
+
+  @override
+  String get fullNameForErrors => name;
+}
+
+/// Represents a [builder] that's being accessed incorrectly. For example, an
+/// attempt to write to a final field, or to read from a setter.
+class AccessErrorBuilder extends ProblemBuilder {
+  AccessErrorBuilder(String name, Builder builder, int charOffset, Uri fileUri)
+      : super(name, builder, charOffset, fileUri);
+
+  Builder get parent => builder;
+
   bool get isFinal => builder.isFinal;
 
   bool get isField => builder.isField;
@@ -163,16 +179,12 @@ class AccessErrorBuilder extends Builder {
 
   bool get isLocal => builder.isLocal;
 
-  bool get hasProblem => true;
+  String get message => "Access error: '$name'.";
 }
 
-class AmbiguousBuilder extends Builder {
-  final Builder builder;
+class AmbiguousBuilder extends ProblemBuilder {
+  AmbiguousBuilder(String name, Builder builder, int charOffset, Uri fileUri)
+      : super(name, builder, charOffset, fileUri);
 
-  AmbiguousBuilder(this.builder, int charOffset, Uri fileUri)
-      : super(null, charOffset, fileUri);
-
-  get target => null;
-
-  bool get hasProblem => true;
+  String get message => "Duplicated named: '$name'.";
 }