Specialize message for parts as entry point

pkg/compiler/lib/src/library_loader.dart

 // 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.
 
 library dart2js.library_loader;
 
 import 'dart:async';
 
 import 'common.dart';
 import 'common/names.dart' show
@@ skipping 631 matching lines @@
         LibraryElement element =
             createLibrarySync(handler, script, resolvedUri);
         CompilationUnitElementX compilationUnit = element.entryCompilationUnit;
         if (compilationUnit.partTag != null) {
           if (skipFileWithPartOfTag) {
             // TODO(johnniwinther): Avoid calling [Compiler.onLibraryCreated]
             // for this library.
             libraryCanonicalUriMap.remove(resolvedUri);
             return null;
           }
-          DiagnosticMessage error = reporter.withCurrentElement(
-              compilationUnit,
-              () => reporter.createMessage(
-                  compilationUnit.partTag, MessageKind.IMPORT_PART_OF));
-          DiagnosticMessage info = reporter.withCurrentElement(
-              importingLibrary,
-              () => reporter.createMessage(
-                  node,
-                  MessageKind.IMPORT_PART_OF_HERE));
-          reporter.reportError(error, <DiagnosticMessage>[info]);
+          if (importingLibrary == null) {
+            DiagnosticMessage error = reporter.withCurrentElement(
+                compilationUnit,
+                () => reporter.createMessage(
+                    compilationUnit.partTag, MessageKind.MAIN_HAS_PART_OF));
+            reporter.reportError(error);
+          } else {
+            DiagnosticMessage error = reporter.withCurrentElement(
+                compilationUnit,
+                () => reporter.createMessage(
+                    compilationUnit.partTag, MessageKind.IMPORT_PART_OF));
+            DiagnosticMessage info = reporter.withCurrentElement(
+                importingLibrary,
+                () => reporter.createMessage(
+                    node,
+                    MessageKind.IMPORT_PART_OF_HERE));
+            reporter.reportError(error, [info]);
+          }
         }
         return processLibraryTags(handler, element).then((_) {
           reporter.withCurrentElement(element, () {
             handler.registerLibraryExports(element);
           });
           return element;
         });
       });
     });
   }
@@ skipping 720 matching lines @@
         }
         suffixes.add(const Link<Uri>().prepend(canonicalUri));
       }
       suffixChainMap[library] = suffixes;
       return;
     }
 
     computeSuffixes(rootLibrary, const Link<Uri>());
   }
 }