dart2js: complain about missing part-of tags.

dart/sdk/lib/_internal/compiler/implementation/compiler.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.
 
 part of dart2js;
 
 /**
  * If true, print a warning for each method that was resolved, but not
  * compiled.
  */
@@ skipping 748 matching lines @@
     reportDiagnostic(span, 'Error: $message', api.Diagnostic.ERROR);
     throw new CompilerCancelledException(message.toString());
   }
 
   void reportMessage(SourceSpan span, Diagnostic message, api.Diagnostic kind) {
     // TODO(ahe): The names Diagnostic and api.Diagnostic are in
     // conflict. Fix it.
     reportDiagnostic(span, "$message", kind);
   }
 
-  void onDeprecatedFeature(Spannable span, String feature) {
+  /// Returns true if a diagnostic was emitted.
+  bool onDeprecatedFeature(Spannable span, String feature) {
     if (currentElement == null)
       throw new SpannableAssertionFailure(span, feature);
     if (!checkDeprecationInSdk &&
         currentElement.getLibrary().isPlatformLibrary) {
-      return;
+      return false;
     }
     var kind = rejectDeprecatedFeatures
         ? api.Diagnostic.ERROR : api.Diagnostic.WARNING;
     var message = rejectDeprecatedFeatures
         ? MessageKind.DEPRECATED_FEATURE_ERROR.error([feature])
         : MessageKind.DEPRECATED_FEATURE_WARNING.error([feature]);
     reportMessage(spanFromSpannable(span), message, kind);
+    return true;
   }
 
   void reportDiagnostic(SourceSpan span, String message, api.Diagnostic kind);
 
   SourceSpan spanFromTokens(Token begin, Token end, [Uri uri]) {
     if (begin == null || end == null) {
       // TODO(ahe): We can almost always do better. Often it is only
       // end that is null. Otherwise, we probably know the current
       // URI.
       throw 'Cannot find tokens to produce error message.';
     }
     if (uri == null && currentElement != null) {
       uri = currentElement.getCompilationUnit().script.uri;
     }
     return SourceSpan.withCharacterOffsets(begin, end,
       (beginOffset, endOffset) => new SourceSpan(uri, beginOffset, endOffset));
   }
 
   SourceSpan spanFromNode(Node node, [Uri uri]) {
     return spanFromTokens(node.getBeginToken(), node.getEndToken(), uri);
   }
 
   SourceSpan spanFromElement(Element element) {
     if (Elements.isErroneousElement(element)) {
       element = element.enclosingElement;
     }
-    if (element.position() == null) {
+    if (element.position() == null && !element.isCompilationUnit()) {
       // Sometimes, the backend fakes up elements that have no
       // position. So we use the enclosing element instead. It is
       // not a good error location, but cancel really is "internal
       // error" or "not implemented yet", so the vicinity is good
       // enough for now.
       element = element.enclosingElement;
       // TODO(ahe): I plan to overhaul this infrastructure anyways.
     }
     if (element == null) {
       element = currentElement;
@@ skipping 121 matching lines @@
   // TODO(johnniwinther): Use [spannable] and [message] to provide better
   // information on assertion errors.
   if (condition is Function){
     condition = condition();
   }
   if (spannable == null || !condition) {
     throw new SpannableAssertionFailure(spannable, message);
   }
   return true;
 }