Improve compile-time error handling.

pkg/front_end/lib/src/fasta/source/source_library_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.source_library_builder;
 
 import 'package:kernel/ast.dart' show
     AsyncMarker,
     ProcedureKind;
 
 import '../combinator.dart' show
     Combinator;
 
 import '../errors.dart' show
-    inputError,
     internalError;
 
 import '../import.dart' show
     Import;
 
 import 'source_loader.dart' show
     SourceLoader;
 
 import '../builder/scope.dart' show
     Scope;
@@ skipping 168 matching lines @@
       ConstructorReferenceBuilder name, List<FormalParameterBuilder> formals,
       AsyncMarker asyncModifier, ConstructorReferenceBuilder redirectionTarget,
       int charOffset);
 
   FormalParameterBuilder addFormalParameter(
       List<MetadataBuilder> metadata, int modifiers,
       T type, String name, bool hasThis, int charOffset);
 
   TypeVariableBuilder addTypeVariable(String name, T bound, int charOffset);
 
-  Builder addBuilder(String name, Builder builder) {
+  Builder addBuilder(String name, Builder builder, int charOffset) {
     // TODO(ahe): Set the parent correctly here. Could then change the
     // implementation of MemberBuilder.isTopLevel to test explicitly for a
     // LibraryBuilder.
     if (currentDeclaration == libraryDeclaration) {
       if (builder is MemberBuilder) {
         builder.parent = this;
       } else if (builder is TypeDeclarationBuilder) {
         builder.parent = this;
       } else if (builder is PrefixBuilder) {
         assert(builder.parent == this);
@@ skipping 12 matching lines @@
         Builder other = existing.exports.putIfAbsent(name, () => builder);
         if (other != builder) {
           existing.exports[name] =
               other.combineAmbiguousImport(name, builder, this);
         }
       });
       return existing;
     } else if (existing != null && (existing.next != null ||
             ((!existing.isGetter || !builder.isSetter) &&
                 (!existing.isSetter || !builder.isGetter)))) {
-      return inputError(uri, -1, "Duplicated definition of $name");
+      addCompileTimeError(charOffset, "Duplicated definition of '$name'.");
     }
     return members[name] = builder;
   }
 
   void buildBuilder(Builder builder);
 
   R build() {
     members.forEach((String name, Builder builder) {
       do {
         buildBuilder(builder);
@@ skipping 27 matching lines @@
         parts.remove(part);
         return;
       }
       if (part.partOf != name) {
         print("${part.uri} is part of '${part.partOf}' but is used as a part "
             "by '${name}' ($uri)");
         parts.remove(part);
         return;
       }
     }
-    part.members.forEach(addBuilder);
+    part.members.forEach((String name, Builder builder) {
+      addBuilder(name, builder, -1);
+    });
     types.addAll(part.types);
     constructorReferences.addAll(part.constructorReferences);
     part.partOfLibrary = this;
     // TODO(ahe): Include metadata from part?
   }
 
   void buildInitialScopes() {
     members.forEach(addToExportScope);
     members.forEach(addToScope);
   }
@@ skipping 116 matching lines @@
           // parent declaration.
           parent.addType(type);
         } else {
           type.bind(builder);
         }
       }
     }
     types.clear();
   }
 }