Report an error when a part-of refers to an unnamed library.

pkg/analyzer/lib/src/dart/analysis/library_analyzer.dart

 // Copyright (c) 2017, 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.
 
 import 'package:analyzer/context/declared_variables.dart';
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/visitor.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/error/error.dart';
 import 'package:analyzer/error/listener.dart';
@@ skipping 466 matching lines @@
                 partUri,
                 [partUri.toSource()]);
           } else {
             String name = nameOrSource.name;
             if (name != null) {
               if (libraryNameNode != null && libraryNameNode.name != name) {
                 libraryErrorReporter.reportErrorForNode(
                     StaticWarningCode.PART_OF_DIFFERENT_LIBRARY,
                     partUri,
                     [libraryNameNode.name, name]);
+              } else if (libraryNameNode == null) {
+                libraryErrorReporter.reportErrorForNode(
+                    StaticWarningCode.PART_OF_UNNAMED_LIBRARY, partUri, [name]);

[Lasse Reichstein Nielsen, 2017/06/08 19:31:19]

Logic seems backwards.
Put the second branch first:
  if (libraryNameNode == null) { 
    ...
  } else if (libraryNameNode.name != name) {
    ...
  }

[floitsch, 2017/06/08 19:47:33]

Done.

               }
             } else {
               Source source = nameOrSource.source;
               if (source != _library.source) {
                 libraryErrorReporter.reportErrorForNode(
                     StaticWarningCode.PART_OF_DIFFERENT_LIBRARY,
                     partUri,
                     [_library.uriStr, source.uri]);
               }
             }
@@ skipping 299 matching lines @@
 }
 
 /**
  * Either the name or the source associated with a part-of directive.
  */
 class _NameOrSource {
   final String name;
   final Source source;
   _NameOrSource(this.name, this.source);
 }