Specialize message for parts as entry point

pkg/compiler/lib/src/diagnostics/dart2js_messages.dart

 // Copyright (c) 2015, 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.
 
 // The messages in this file should meet the following guide lines:
 //
 // 1. The message should be a complete sentence starting with an uppercase
 // letter, and ending with a period.
 //
 // 2. Reserved words and embedded identifiers should be in single quotes, so
@@ skipping 1759 matching lines @@
 """
       }
     ],
   },
 
   'IMPORT_PART_OF_HERE': {
     'id': 'TRSZOJ',
     'template': 'The library is imported here.',
   },
 
+  'MAIN_HAS_PART_OF': {
+    'id': 'MFMRRL',
+    'template': "The main application file must not have a 'part-of' "
+                "directive.",
+    'howToFix': "Try removing the 'part-of' directive or starting compilation "
+                "from another file.",
+    'examples': [
+      {
+        'main.dart': """
+part of library;
+
+main() {}
+"""
+      }
+    ],
+  },
+
   'LIBRARY_NAME_MISMATCH': {
     'id': 'AXGYPQ',
     'template': "Expected part of library name '#{libraryName}'.",
     'howToFix': "Try changing the directive to 'part of #{libraryName};'.",
     'examples': [
       {
         'main.dart': """
 library lib.foo;
 
 part 'part.dart';
@@ skipping 1916 matching lines @@
         "more code and prevents the compiler from doing some optimizations.",
     'howToFix': "Consider removing this 'noSuchMethod' implementation."
   },
 
   'UNRECOGNIZED_VERSION_OF_LOOKUP_MAP': {
     'id': 'OVAFEW',
     'template': "Unsupported version of package:lookup_map.",
     'howToFix': DONT_KNOW_HOW_TO_FIX
   },
 };