Move "null2" getter from ConstantVisitor to TypeProvider.

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 739 matching lines @@
         new HashMap<String, DartObjectImpl>();
     HashMap<String, NamedExpression> namedArgumentNodes =
         new HashMap<String, NamedExpression>();
     for (int i = 0; i < argumentCount; i++) {
       Expression argument = arguments[i];
       if (argument is NamedExpression) {
         String name = argument.name.label.name;
         namedArgumentValues[name] =
             constantVisitor._valueOf(argument.expression);
         namedArgumentNodes[name] = argument;
-        argumentValues[i] = constantVisitor.null2;
+        argumentValues[i] = typeProvider.nullObject;
       } else {
         argumentValues[i] = constantVisitor._valueOf(argument);
         argumentNodes[i] = argument;
       }
     }
     constructor = _followConstantRedirectionChain(constructor);
     InterfaceType definingClass = constructor.returnType as InterfaceType;
     if (constructor.isFactory) {
       // We couldn't find a non-factory constructor.
       // See if it's because we reached an external const factory constructor
@@ skipping 90 matching lines @@
         // direct error messages to the constructor call.
         errorTarget = node;
       }
       if (argumentValue == null && baseParameter is ParameterElementImpl) {
         // The parameter is an optional positional parameter for which no value
         // was provided, so use the default value.
         beforeGetParameterDefault(baseParameter);
         EvaluationResultImpl evaluationResult = baseParameter.evaluationResult;
         if (evaluationResult == null) {
           // No default was provided, so the default value is null.
-          argumentValue = constantVisitor.null2;
+          argumentValue = typeProvider.nullObject;
         } else if (evaluationResult.value != null) {
           argumentValue = evaluationResult.value;
         }
       }
       if (argumentValue != null) {
         if (!_runtimeTypeMatch(argumentValue, parameter.type)) {
           errorReporter.reportErrorForNode(
               CheckedModeCompileTimeErrorCode.CONST_CONSTRUCTOR_PARAM_TYPE_MISMATCH,
               errorTarget, [argumentValue.type, parameter.type]);
         }
@@ skipping 276 matching lines @@
  *   <i>e<sub>3</sub></i> are constant expressions, and <i>e<sub>1</sub></i>
  *   evaluates to a boolean value.
  * </blockquote>
  */
 class ConstantVisitor extends UnifyingAstVisitor<DartObjectImpl> {
   /**
    * The type provider used to access the known types.
    */
   final TypeProvider _typeProvider;
 
-  /**
-   * An shared object representing the value 'null'.
-   */
-  DartObjectImpl _nullObject;
-
   HashMap<String, DartObjectImpl> _lexicalEnvironment;
 
   /**
    * Error reporter that we use to report errors accumulated while computing the
    * constant.
    */
   final ErrorReporter _errorReporter;
 
   /**
    * Helper class used to compute constant values.
@@ skipping 19 matching lines @@
    * found during evaluation.
    */
   ConstantVisitor.con2(this._typeProvider,
       HashMap<String, DartObjectImpl> lexicalEnvironment, this._errorReporter) {
     this._lexicalEnvironment = lexicalEnvironment;
     this._dartObjectComputer =
         new DartObjectComputer(_errorReporter, _typeProvider);
   }
 
   /**
-   * Return an object representing the value 'null'.
-   */
-  DartObjectImpl get null2 {
-    if (_nullObject == null) {
-      _nullObject =
-          new DartObjectImpl(_typeProvider.nullType, NullState.NULL_STATE);
-    }
-    return _nullObject;
-  }
-
-  /**
    * This method is called just before retrieving an evaluation result from an
    * AST node. Unit tests will override it to introduce additional error
    * checking.
    */
   void beforeGetEvaluationResult(AstNode node) {}
 
   /**
    * Return `true` if the given [element] represents the `length` getter in
    * class 'String'.
    */
@@ skipping 264 matching lines @@
       node.expression.accept(this);
 
   @override
   DartObjectImpl visitNode(AstNode node) {
     // TODO(brianwilkerson) Figure out which error to report.
     _error(node, null);
     return null;
   }
 
   @override
-  DartObjectImpl visitNullLiteral(NullLiteral node) => null2;
+  DartObjectImpl visitNullLiteral(NullLiteral node) => _typeProvider.nullObject;
 
   @override
   DartObjectImpl visitParenthesizedExpression(ParenthesizedExpression node) =>
       node.expression.accept(this);
 
   @override
   DartObjectImpl visitPrefixedIdentifier(PrefixedIdentifier node) {
     // String.length
     {
       Element element = node.staticElement;
@@ skipping 152 matching lines @@
 
   /**
    * Return the value of the given [expression], or a representation of 'null'
    * if the expression cannot be evaluated.
    */
   DartObjectImpl _valueOf(Expression expression) {
     DartObjectImpl expressionValue = expression.accept(this);
     if (expressionValue != null) {
       return expressionValue;
     }
-    return null2;
+    return _typeProvider.nullObject;
   }
 }
 
 /**
  * The state of a Dart object.
  */
 abstract class DartObject {
   /**
    * Return the boolean value of this object, or `null` if either the value of
    * this object is not known or this object is not of type 'bool'.
@@ skipping 3382 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;
 }