Revert "Revert "fix #26141, add support for type arguments to constants""

pkg/analyzer/lib/src/dart/constant/value.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.
 
 /**
  * The implementation of the class [DartObject].
  */
 library analyzer.src.dart.constant.value;
 
 import 'dart:collection';
@@ skipping 702 matching lines @@
     if (state is SymbolState) {
       return state.value;
     }
     return null;
   }
 
   @override
   DartType toTypeValue() {
     InstanceState state = _state;
     if (state is TypeState) {
-      Element element = state._element;
-      if (element is TypeDefiningElement) {
-        return element.type;
-      }
+      return state._type;
     }
     return null;
   }
 }
 
 /**
  * The state of an object representing a double.
  */
 class DoubleState extends NumState {
   /**
@@ skipping 2027 matching lines @@
   String toString() => value == null ? "-unknown-" : "#$value";
 }
 
 /**
  * The state of an object representing a type.
  */
 class TypeState extends InstanceState {
   /**
    * The element representing the type being modeled.
    */
-  final Element _element;
+  final DartType _type;
 
   /**
    * Initialize a newly created state to represent the given [value].
    */
-  TypeState(this._element);
+  TypeState(this._type);
 
   @override
-  int get hashCode => _element == null ? 0 : _element.hashCode;
+  int get hashCode => _type?.hashCode ?? 0;
 
   @override
   String get typeName => "Type";
 
   @override
   bool operator ==(Object object) =>
-      object is TypeState && (_element == object._element);
+      object is TypeState && (_type == object._type);
 
   @override
   StringState convertToString() {
-    if (_element == null) {
+    if (_type == null) {
       return StringState.UNKNOWN_VALUE;
     }
-    return new StringState(_element.name);
+    return new StringState(_type.displayName);
   }
 
   @override
   BoolState equalEqual(InstanceState rightOperand) {
     assertBoolNumStringOrNull(rightOperand);
     return isIdentical(rightOperand);
   }
 
   @override
   BoolState isIdentical(InstanceState rightOperand) {
-    if (_element == null) {
+    if (_type == null) {
       return BoolState.UNKNOWN_VALUE;
     }
     if (rightOperand is TypeState) {
-      Element rightElement = rightOperand._element;
-      if (rightElement == null) {
+      DartType rightType = rightOperand._type;
+      if (rightType == null) {
         return BoolState.UNKNOWN_VALUE;
       }
-      return BoolState.from(_element == rightElement);
+      return BoolState.from(_type == rightType);
     } else if (rightOperand is DynamicState) {
       return BoolState.UNKNOWN_VALUE;
     }
     return BoolState.FALSE_STATE;
   }
 
   @override
-  String toString() => _element == null ? "-unknown-" : _element.name;
+  String toString() => _type?.toString() ?? "-unknown-";
 }