Issue 5722. Better 'missing part of' error message. Quick Fix for it.

compiler/java/com/google/dart/compiler/DartCompilerErrorCode.java

 // Copyright (c) 2012, 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.
 
 package com.google.dart.compiler;
 
 /**
  * Valid error codes for the errors produced by the Dart compiler.
  */
 public enum DartCompilerErrorCode implements ErrorCode {
   CONSOLE_WEB_MIX(ErrorSeverity.INFO,
       "Libraries 'dart:io' (console apps only) and 'dart:html' (web apps only) cannot be used together"),
   ENTRY_POINT_METHOD_CANNOT_HAVE_PARAMETERS(ErrorSeverity.WARNING, 
       "Main entry point method cannot have parameters"),
   ENTRY_POINT_METHOD_MAY_NOT_BE_GETTER(ErrorSeverity.WARNING,
       "Entry point \"%s\" may not be a getter"),
   ENTRY_POINT_METHOD_MAY_NOT_BE_SETTER(ErrorSeverity.WARNING,
       "Entry point \"%s\" may not be a setter"),
   ILLEGAL_DIRECTIVES_IN_SOURCED_UNIT("This part was included by %s via a "
       + "part directive, so cannot itself contain directives other than a 'part of' directive"),
   IO("Input/Output error: %s"),
   MIRRORS_NOT_FULLY_IMPLEMENTED(ErrorSeverity.WARNING, "dart:mirrors is not fully implemented yet"),
   MISSING_LIBRARY_DIRECTIVE("a library which is imported is missing a library directive: %s"),
   MISSING_SOURCE("Cannot find referenced source: %s"),
-  MISSING_PART_OF_DIRECTIVE("Missing 'part of' directive"),
+  MISSING_PART_OF_DIRECTIVE("Unit is part of library '%s', but has no 'part of' directive"),
   UNIT_WAS_ALREADY_INCLUDED("Unit '%s' was already included"),
   WRONG_PART_OF_NAME(
       ErrorSeverity.WARNING,
       "This part was included by '%s' via a 'part' directive, but uses name '%s' in 'part of' directive");
   private final ErrorSeverity severity;
   private final String message;
 
   /**
    * Initialize a newly created error code to have the given message and ERROR severity.
    */
@@ skipping 22 matching lines @@
   @Override
   public SubSystem getSubSystem() {
     return SubSystem.COMPILER;
   }
 
   @Override
   public boolean needsRecompilation() {
     return true;
   }
 }