Implement part-of directive.

dart/lib/compiler/implementation/scanner/scanner_task.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.
 
 class ScannerTask extends CompilerTask {
   ScannerTask(Compiler compiler) : super(compiler);
   String get name => 'Scanner';
 
+  final Map<String, LibraryElement> libraryNames =
+      new Map<String, LibraryElement>();
+
   void scanLibrary(LibraryElement library) {
     var compilationUnit = library.entryCompilationUnit;
     compiler.log("scanning library ${compilationUnit.script.name}");
     scan(compilationUnit);
     processLibraryTags(library);
   }
 
   void scan(CompilationUnitElement compilationUnit) {
     measure(() {
       scanElements(compilationUnit);
@@ skipping 29 matching lines @@
         // before it fully declares all the members that are sourced
         // in.
         imports.addLast(tag);
       } else if (tag.isLibraryName) {
         tagState = checkTag(TagState.LIBRARY, tag);
         if (library.libraryTag !== null) {
           compiler.cancel("duplicated library declaration", node: tag);
         } else {
           library.libraryTag = tag;
         }
+        checkDuplicatedLibraryName(library);
       } else if (tag.isPart) {
         StringNode uri = tag.uri;
         Uri resolved = base.resolve(uri.dartString.slowToString());
         tagState = checkTag(TagState.SOURCE, tag);
         loadPart(tag, resolved, library);
       } else {
         compiler.internalError("Unhandled library tag.", node: tag);
       }
     }
 
     // Apply patch, if any.
     if (library.uri.scheme == 'dart') {
       compiler.patchDartLibrary(library, library.uri.path);
     }
 
     // Now that we have processed all the source tags, it is safe to
     // start loading other libraries.
 
     if (library.uri.scheme != 'dart' || library.uri.path != 'core') {
       compiler.importCoreLibrary(library);
     }
 
     for (Import tag in imports.toLink()) {
       importLibraryFromTag(tag, library.entryCompilationUnit);
     }
   }
 
+  void checkDuplicatedLibraryName(LibraryElement library) {
+    LibraryTag tag = library.libraryTag;
+    if (tag != null) {
+      String name = library.getLibraryOrScriptName();
+      LibraryElement existing =
+          libraryNames.putIfAbsent(name, () => library);
+      if (existing !== library) {
+        Uri uri = library.entryCompilationUnit.script.uri;
+        compiler.reportMessage(
+            compiler.spanFromNode(tag.name, uri),
+            MessageKind.DUPLICATED_LIBRARY_NAME.error([name]),
+            api_s.Diagnostic.WARNING);
+        Uri existingUri = existing.entryCompilationUnit.script.uri;
+        compiler.reportMessage(
+            compiler.spanFromNode(existing.libraryTag.name, existingUri),
+            MessageKind.DUPLICATED_LIBRARY_NAME.error([name]),
+            api_s.Diagnostic.WARNING);
+      }
+    }
+  }
+
   /**
    * Handle a part tag in the scope of [library]. The [path] given is used as
    * is, any resolution should be done beforehand.
    */
   void loadPart(Part part, Uri path, LibraryElement library) {
     Script sourceScript = compiler.readScript(path, part.uri);
     CompilationUnitElement unit =
         new CompilationUnitElement(sourceScript, library);
     compiler.withCurrentElement(unit, () => compiler.scanner.scan(unit));
   }
@@ skipping 123 matching lines @@
   static const int RESOURCE = 4;
 
   /** Next state. */
   static const List<int> NEXT =
       const <int>[NO_TAG_SEEN,
                   IMPORT, // Only one library tag is allowed.
                   IMPORT,
                   SOURCE,
                   RESOURCE];
 }