Generate the proper error when a constant refers to itself.

pkg/analyzer/lib/src/generated/constant.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.
 
 // This code was auto-generated, is not intended to be edited, and is subject to
 // significant change. Please see the README file for more information.
 
 library engine.constant;
 
 import 'dart:collection';
@@ skipping 1255 matching lines @@
       referenceGraph.addNode(constant);
       evaluationEngine.computeDependencies(constant,
           (ConstantEvaluationTarget dependency) {
         referenceGraph.addEdge(constant, dependency);
       });
     }
     List<List<ConstantEvaluationTarget>> topologicalSort =
         referenceGraph.computeTopologicalSort();
     for (List<ConstantEvaluationTarget> constantsInCycle in topologicalSort) {
       if (constantsInCycle.length == 1) {
-        _computeValueFor(constantsInCycle[0]);
-      } else {
-        for (ConstantEvaluationTarget constant in constantsInCycle) {
-          evaluationEngine.generateCycleError(constantsInCycle, constant);
+        ConstantEvaluationTarget constant = constantsInCycle[0];
+        if (!referenceGraph.getTails(constant).contains(constant)) {
+          _computeValueFor(constant);
+          continue;
         }
       }
+      for (ConstantEvaluationTarget constant in constantsInCycle) {
+        evaluationEngine.generateCycleError(constantsInCycle, constant);
+      }
     }
   }
 
   /**
    * Compute a value for the given [constant].
    */
   void _computeValueFor(ConstantEvaluationTarget constant) {
     if (!_constantsToCompute.contains(constant)) {
       // Element is in the dependency graph but should have been computed by
       // a previous stage of analysis.
@@ skipping 3923 matching lines @@
       return BoolState.from(_element == rightElement);
     } else if (rightOperand is DynamicState) {
       return BoolState.UNKNOWN_VALUE;
     }
     return BoolState.FALSE_STATE;
   }
 
   @override
   String toString() => _element == null ? "-unknown-" : _element.name;
 }