Fix for adding new elements into library cycles.

pkg/analyzer/test/src/context/context_test.dart

 // Copyright (c) 2014, 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 analyzer.test.src.context.context_test;
 
 import 'dart:async';
 import 'dart:collection';
 
 import 'package:analyzer/dart/ast/ast.dart';
@@ skipping 469 matching lines @@
     // The reason is that a.dart adds dependencies on (not existing) b.dart
     // results in cache.
     // Now a.dart does not have errors.
     addSource('/b.dart', codeB);
     expect(getErrorsState(a), CacheState.INVALID);
     _performPendingAnalysisTasks();
     expect(getErrorsState(a), CacheState.VALID);
     expect(context.getErrors(a).errors, hasLength(0));
   }
 
+  void test_applyChanges_addNewImport_invalidateLibraryCycle() {
+    context.analysisOptions =
+        new AnalysisOptionsImpl.from(context.analysisOptions)
+          ..strongMode = true;
+    Source embedder = addSource(
+        '/a.dart',
+        r'''
+library a;
+import 'b.dart';
+//import 'c.dart';
+''');
+    addSource(
+        '/b.dart',
+        r'''
+library b;
+import 'a.dart';
+''');
+    addSource(
+        '/c.dart',
+        r'''
+library c;
+import 'b.dart';
+''');
+    _performPendingAnalysisTasks();
+    // Add a new import into a.dart, this should invalidate its library cycle.
+    // If it doesn't, we will get a task cycle exception.
+    context.setContents(
+        embedder,
+        r'''
+library a;
+import 'b.dart';
+import 'c.dart';
+''');
+    _performPendingAnalysisTasks();
+    expect(context.getCacheEntry(embedder).exception, isNull);
+  }
+
   void test_cacheConsistencyValidator_computed_deleted() {
     CacheConsistencyValidator validator = context.cacheConsistencyValidator;
     var stat = PerformanceStatistics.cacheConsistencyValidationStatistics;
     stat.reset();
     // Add sources.
     MemoryResourceProvider resourceProvider = new MemoryResourceProvider();
     String path1 = '/test1.dart';
     String path2 = '/test2.dart';
     Source source1 = resourceProvider.newFile(path1, '// 1-1').createSource();
     Source source2 = resourceProvider.newFile(path2, '// 2-1').createSource();
@@ skipping 4644 matching lines @@
    * Initialize the visitor.
    */
   _ElementGatherer();
 
   @override
   void visitElement(Element element) {
     elements[element] = element;
     super.visitElement(element);
   }
 }