Report a compile-time error if a const field is multiply initialized.

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 729 matching lines @@
               // We've already checked that the argument can be assigned to the
               // parameter; we also need to check that it can be assigned to
               // the field.
               if (!runtimeTypeMatch(argumentValue, fieldType)) {
                 errorReporter.reportErrorForNode(
                     CheckedModeCompileTimeErrorCode.CONST_CONSTRUCTOR_PARAM_TYPE_MISMATCH,
                     errorTarget, [argumentValue.type, fieldType]);
               }
             }
             String fieldName = field.name;
+            if (fieldMap.containsKey(fieldName)) {
+              errorReporter.reportErrorForNode(
+                  CompileTimeErrorCode.CONST_EVAL_THROWS_EXCEPTION, node);
+            }
             fieldMap[fieldName] = argumentValue;
           }
         } else {
           String name = baseParameter.name;
           parameterMap[name] = argumentValue;
         }
       }
     }
     ConstantVisitor initializerVisitor = new ConstantVisitor(
         this, errorReporter, lexicalEnvironment: parameterMap);
     String superName = null;
     NodeList<Expression> superArguments = null;
     for (ConstructorInitializer initializer in initializers) {
       if (initializer is ConstructorFieldInitializer) {
         ConstructorFieldInitializer constructorFieldInitializer = initializer;
         Expression initializerExpression =
             constructorFieldInitializer.expression;
         DartObjectImpl evaluationResult =
             initializerExpression.accept(initializerVisitor);
         if (evaluationResult != null) {
           String fieldName = constructorFieldInitializer.fieldName.name;
+          if (fieldMap.containsKey(fieldName)) {
+            errorReporter.reportErrorForNode(
+                CompileTimeErrorCode.CONST_EVAL_THROWS_EXCEPTION, node);
+          }
           fieldMap[fieldName] = evaluationResult;
           PropertyAccessorElement getter = definingClass.getGetter(fieldName);
           if (getter != null) {
             PropertyInducingElement field = getter.variable;
             if (!runtimeTypeMatch(evaluationResult, field.type)) {
               errorReporter.reportErrorForNode(
                   CheckedModeCompileTimeErrorCode.CONST_CONSTRUCTOR_FIELD_TYPE_MISMATCH,
                   node, [evaluationResult.type, fieldName, field.type]);
             }
           }
@@ skipping 4461 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;
 }