Fix constant evaluation logic for String.length.

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 1296 matching lines @@
         new DartObjectComputer(_errorReporter, _typeProvider);
   }
 
   /**
    * 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'.
-   */
-  bool isStringLength(Element element) {
-    if (element is PropertyAccessorElement) {
-      if (element.isGetter && element.name == 'length') {
-        return element.enclosingElement == _typeProvider.stringType.element;
-      }
-    }
-    return false;
-  }
-
   @override
   DartObjectImpl visitAdjacentStrings(AdjacentStrings node) {
     DartObjectImpl result = null;
     for (StringLiteral string in node.strings) {
       if (result == null) {
         result = string.accept(this);
       } else {
         result =
             _dartObjectComputer.concatenate(node, result, string.accept(this));
       }
@@ skipping 253 matching lines @@
 
   @override
   DartObjectImpl visitNullLiteral(NullLiteral node) => _typeProvider.nullObject;
 
   @override
   DartObjectImpl visitParenthesizedExpression(ParenthesizedExpression node) =>
       node.expression.accept(this);
 
   @override
   DartObjectImpl visitPrefixedIdentifier(PrefixedIdentifier node) {
+    SimpleIdentifier prefixNode = node.prefix;
+    Element prefixElement = prefixNode.staticElement;
     // String.length
-    {
-      Element element = node.staticElement;
-      if (isStringLength(element)) {
-        DartObjectImpl prefixResult = node.prefix.accept(this);
+    if (prefixElement is! PrefixElement && prefixElement is! ClassElement) {
+      DartObjectImpl prefixResult = node.prefix.accept(this);
+      if (_isStringLength(prefixResult, node.identifier)) {
         return prefixResult.stringLength(_typeProvider);
       }
     }
     // importPrefix.CONST
-    SimpleIdentifier prefixNode = node.prefix;
-    Element prefixElement = prefixNode.staticElement;
     if (prefixElement is! PrefixElement) {
       DartObjectImpl prefixResult = prefixNode.accept(this);
       if (prefixResult == null) {
         // The error has already been reported.
         return null;
       }
     }
     // validate prefixed identifier
     return _getConstantValue(node, node.staticElement);
   }
@@ skipping 16 matching lines @@
         // TODO(brianwilkerson) Figure out which error to report.
         _error(node, null);
         return null;
       }
       break;
     }
   }
 
   @override
   DartObjectImpl visitPropertyAccess(PropertyAccess node) {
-    Element element = node.propertyName.staticElement;
-    if (isStringLength(element)) {
-      DartObjectImpl prefixResult = node.realTarget.accept(this);
-      return prefixResult.stringLength(_typeProvider);
+    if (node.target != null) {
+      DartObjectImpl prefixResult = node.target.accept(this);
+      if (_isStringLength(prefixResult, node.propertyName)) {
+        return prefixResult.stringLength(_typeProvider);
+      }
     }
-    return _getConstantValue(node, element);
+    return _getConstantValue(node, node.propertyName.staticElement);
   }
 
   @override
   DartObjectImpl visitSimpleIdentifier(SimpleIdentifier node) {
     if (_lexicalEnvironment != null &&
         _lexicalEnvironment.containsKey(node.name)) {
       return _lexicalEnvironment[node.name];
     }
     return _getConstantValue(node, node.staticElement);
   }
@@ skipping 70 matching lines @@
         element is FunctionTypeAliasElement ||
         element is DynamicElementImpl) {
       return new DartObjectImpl(_typeProvider.typeType, new TypeState(element));
     }
     // TODO(brianwilkerson) Figure out which error to report.
     _error(node, null);
     return null;
   }
 
   /**
+   * Return `true` if the given [targetResult] represents a string and the
+   * [identifier] is "length".
+   */
+  bool _isStringLength(
+      DartObjectImpl targetResult, SimpleIdentifier identifier) {
+    if (targetResult == null || targetResult.type != _typeProvider.stringType) {
+      return false;
+    }
+    return identifier.name == 'length';
+  }
+
+  /**
    * 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 _typeProvider.nullObject;
   }
@@ skipping 3413 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;
 }