Fix NPE when computing dependencies of enum constants

pkg/analyzer/test/src/task/dart_test.dart

 // Copyright (c) 2015, 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 test.src.task.dart_test;
 
 import 'package:analyzer/src/context/cache.dart';
 import 'package:analyzer/src/generated/ast.dart';
 import 'package:analyzer/src/generated/constant.dart';
 import 'package:analyzer/src/generated/element.dart';
@@ skipping 1271 matching lines @@
     Element x = accessors.firstWhere((PropertyAccessorElement accessor) =>
         accessor.isGetter && accessor.name == 'x').variable;
     Annotation annotation = findClassAnnotation(unit, 'C');
     // Now compute the dependencies for the annotation, and check that it is
     // the list [x].
     _computeResult(new ConstantEvaluationTarget_Annotation(
         context, source, source, annotation), CONSTANT_DEPENDENCIES);
     expect(outputs[CONSTANT_DEPENDENCIES], [x]);
   }
 
+  test_enumConstant() {
+    Source source = newSource('/test.dart', '''
+enum E {A, B, C}
+''');
+    // First compute the resolved unit for the source.
+    LibrarySpecificUnit librarySpecificUnit =
+        new LibrarySpecificUnit(source, source);
+    _computeResult(librarySpecificUnit, RESOLVED_UNIT2);
+    CompilationUnit unit = outputs[RESOLVED_UNIT2];
+    // Find the element for 'A'
+    EnumDeclaration enumDeclaration = unit.declarations[0];
+    EnumConstantDeclaration constantDeclaration = enumDeclaration.constants[0];
+    FieldElement constantElement = constantDeclaration.element;
+    // Now compute the dependencies for the constant and check that there are
+    // none.
+    _computeResult(constantElement, CONSTANT_DEPENDENCIES);
+    expect(outputs[CONSTANT_DEPENDENCIES], isEmpty);
+  }
+
   test_perform() {
     Source source = newSource('/test.dart', '''
 const x = y;
 const y = 1;
 ''');
     // First compute the resolved unit for the source.
     LibrarySpecificUnit librarySpecificUnit =
         new LibrarySpecificUnit(source, source);
     _computeResult(librarySpecificUnit, RESOLVED_UNIT1);
     CompilationUnit unit = outputs[RESOLVED_UNIT1];
@@ skipping 1193 matching lines @@
   /**
    * Fill [errorListener] with [result] errors in the current [task].
    */
   void _fillErrorListener(ResultDescriptor<List<AnalysisError>> result) {
     List<AnalysisError> errors = task.outputs[result];
     expect(errors, isNotNull, reason: result.name);
     errorListener = new GatheringErrorListener();
     errorListener.addAll(errors);
   }
 }