Ensure locations are always provided, but don't store them yet.

pkg/front_end/lib/src/fasta/builder/scope.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.scope;
 
 import 'builder.dart' show
     Builder,
     MixedAccessor;
 
@@ skipping 11 matching lines @@
   /// Indicates whether an attempt to declare new names in this scope should
   /// succeed.
   final bool isModifiable;
 
   Scope(this.local, this.parent, {this.isModifiable: true});
 
   Scope createNestedScope({bool isModifiable: true}) {
     return new Scope(<String, Builder>{}, this, isModifiable: isModifiable);
   }
 
-  Builder lookup(String name) {
+  Builder lookup(String name, int charOffset, Uri fileUri) {
     Builder builder = local[name];
     if (builder != null) {
-      if (builder.next != null) return lookupAmbiguous(name, builder, false);
-      return builder.isSetter ? new AccessErrorBuilder(builder) : builder;
+      if (builder.next != null) {
+        return lookupAmbiguous(name, builder, false, charOffset, fileUri);
+      }
+      return builder.isSetter
+          ? new AccessErrorBuilder(builder, charOffset, fileUri)
+          : builder;
     } else {
-      return parent?.lookup(name);
+      return parent?.lookup(name, charOffset, fileUri);
     }
   }
 
-  Builder lookupSetter(String name) {
+  Builder lookupSetter(String name, int charOffset, Uri fileUri) {
     Builder builder = local[name];
     if (builder != null) {
-      if (builder.next != null) return lookupAmbiguous(name, builder, true);
+      if (builder.next != null) {
+        return lookupAmbiguous(name, builder, true, charOffset, fileUri);
+      }
       if (builder.isField) {
         if (builder.isFinal) {
-          return new AccessErrorBuilder(builder);
+          return new AccessErrorBuilder(builder, charOffset, fileUri);
         } else {
           return builder;
         }
       } else if (builder.isSetter) {
         return builder;
       } else {
-        return new AccessErrorBuilder(builder);
+        return new AccessErrorBuilder(builder, charOffset, fileUri);
       }
     } else {
-      return parent?.lookupSetter(name);
+      return parent?.lookupSetter(name, charOffset, fileUri);
     }
   }
 
-  Builder lookupAmbiguous(String name, Builder builder, bool setter) {
+  Builder lookupAmbiguous(String name, Builder builder, bool setter,
+      int charOffset, Uri fileUri) {
     assert(builder.next != null);
     if (builder is MixedAccessor) {
       return setter ? builder.setter : builder.getter;
     }
     Builder setterBuilder;
     Builder getterBuilder;
     Builder current = builder;
     while (current != null) {
       if (current.isGetter && getterBuilder == null) {
         getterBuilder = current;
       } else if (current.isSetter && setterBuilder == null) {
         setterBuilder = current;
       } else {
-        return new AmbiguousBuilder(builder);
+        return new AmbiguousBuilder(builder, charOffset, fileUri);
       }
       current = current.next;
     }
     assert(getterBuilder != null);
     assert(setterBuilder != null);
     return setter ? setterBuilder : getterBuilder;
   }
 
   // TODO(ahe): Rename to extend or something.
   void operator[]= (String name, Builder member) {
     if (isModifiable) {
       local[name] = member;
     } else {
       internalError("Can't extend an unmodifiable scope.");
     }
   }
 }
 
 class AccessErrorBuilder extends Builder {
   final Builder builder;
 
-  AccessErrorBuilder(this.builder);
+  AccessErrorBuilder(this.builder, int charOffset, Uri fileUri)
+      : super(null, charOffset, fileUri);
 
   Builder get parent => builder;
 
   get target => null;
 
   bool get isFinal => builder.isFinal;
 
   bool get isField => builder.isField;
 
   bool get isRegularMethod => builder.isRegularMethod;
@@ skipping 11 matching lines @@
   bool get isTypeDeclaration => builder.isTypeDeclaration;
 
   bool get isLocal => builder.isLocal;
 
   bool get hasProblem => true;
 }
 
 class AmbiguousBuilder extends Builder {
   final Builder builder;
 
-  AmbiguousBuilder(this.builder);
+  AmbiguousBuilder(this.builder, int charOffset, Uri fileUri)
+      : super(null, charOffset, fileUri);
 
   get target => null;
 
   bool get hasProblem => true;
 }