Error on part of self.

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;
 
@@ skipping 316 matching lines @@
     }
     if (exporters.isNotEmpty) {
       Export export = exporters.first;
       inputError(
           export.fileUri, export.charOffset, "A part can't be exported.");
     }
   }
 
   void includeParts() {
     for (SourceLibraryBuilder<T, R> part in parts.toList()) {
-      includePart(part);
+      if (part == this) {
+        addCompileTimeError(-1, "A file can't be a part of itself.");
+      } else {
+        includePart(part);
+      }
     }
   }
 
   void includePart(SourceLibraryBuilder<T, R> part) {
     if (name != null) {
       if (part.partOf == null) {
         warning(
             part.fileUri,
             -1,
             "Has no 'part of' declaration but is used as "
@@ skipping 166 matching lines @@
   }
 
   /// Called to register [procedure] as a factory whose types are collected in
   /// [factoryDeclaration]. Later, once the class has been built, we can
   /// synthesize type variables on the factory matching the class'.
   void addFactoryDeclaration(
       ProcedureBuilder procedure, DeclarationBuilder<T> factoryDeclaration) {
     factoryDeclarations[procedure] = factoryDeclaration;
   }
 }