Implement new constant expressions

editor/tools/plugins/com.google.dart.engine/src/com/google/dart/engine/internal/constant/ConstantVisitor.java

Index: editor/tools/plugins/com.google.dart.engine/src/com/google/dart/engine/internal/constant/ConstantVisitor.java
diff --git a/editor/tools/plugins/com.google.dart.engine/src/com/google/dart/engine/internal/constant/ConstantVisitor.java b/editor/tools/plugins/com.google.dart.engine/src/com/google/dart/engine/internal/constant/ConstantVisitor.java
index 132a7149c39834e5c3bd9c5b471583f9f122298c..34c42b04e1985a6e0d0fdd1f241e881bdd5cf407 100644
--- a/editor/tools/plugins/com.google.dart.engine/src/com/google/dart/engine/internal/constant/ConstantVisitor.java
+++ b/editor/tools/plugins/com.google.dart.engine/src/com/google/dart/engine/internal/constant/ConstantVisitor.java
@@ -394,10 +394,18 @@ public class ConstantVisitor extends UnifyingAstVisitor<EvaluationResultImpl> {
 
   @Override
   public EvaluationResultImpl visitPrefixedIdentifier(PrefixedIdentifier node) {
-    // validate prefix
     SimpleIdentifier prefixNode = node.getPrefix();
     Element prefixElement = prefixNode.getStaticElement();
-    if (!(prefixElement instanceof PrefixElement)) {
+    if (prefixElement instanceof PropertyAccessorElement) {
+      PropertyAccessorElement accessor = (PropertyAccessorElement) prefixElement;
+      if (accessor.getName().equals("length")) {

[Paul Berry, 2014/09/18 00:05:06]

I'm confused.  It seems to me that the case we need to handle is something like
this (where we're evaluating x):

  const String s = "foo";
  const int x = s.length;

In which case, when we get here, prefixNode, prefixElement, and accessor refer
to "s", not "length".  So it seems like the thing we should be comparing to
"length" is node.getIdentifier().

[Brian Wilkerson, 2014/09/18 20:29:26]

No, I was. Reworked.

+        Element parent = accessor.getEnclosingElement();
+        if (parent instanceof ClassElement && ((ClassElement) parent).getName().equals("String")) {

[Paul Berry, 2014/09/18 00:05:06]

It's not sufficient to check whether the class's name is "String", because it
could be a class String declared elsewhere.

E.g. this is legal (albeit contrived) dart code:

  import 'dart:core' as core;
  class String {
    ...
  }

We need to check whether parent is the "String" class from dart:core.

[Brian Wilkerson, 2014/09/18 20:29:26]

Thanks! I forgot to come back to this.

+          EvaluationResultImpl target = node.getPrefix().accept(this);
+          return target.stringLength(typeProvider, node);
+        }
+      }
+    } else if (!(prefixElement instanceof PrefixElement)) {

[Paul Berry, 2014/09/18 00:05:06]

I'm not convinced that "else" is correct here.  It seems like we need a brand
new "if" statement, so that if the above code fails to return for any reason,
we'll still do this "if" test.

[Brian Wilkerson, 2014/09/18 20:29:26]

I agree. Done.

       EvaluationResultImpl prefixResult = prefixNode.accept(this);
       if (!(prefixResult instanceof ValidResult)) {
         return error(node, null);
@@ -428,7 +436,18 @@ public class ConstantVisitor extends UnifyingAstVisitor<EvaluationResultImpl> {
 
   @Override
   public EvaluationResultImpl visitPropertyAccess(PropertyAccess node) {
-    return getConstantValue(node, node.getPropertyName().getStaticElement());
+    Element element = node.getPropertyName().getStaticElement();
+    if (element instanceof PropertyAccessorElement) {
+      PropertyAccessorElement accessor = (PropertyAccessorElement) element;
+      if (accessor.getName().equals("length")) {
+        Element parent = accessor.getEnclosingElement();
+        if (parent instanceof ClassElement && ((ClassElement) parent).getName().equals("String")) {

[Paul Berry, 2014/09/18 00:05:07]

As above, it's not sufficient to check whether the class's name is "String".

[Brian Wilkerson, 2014/09/18 20:29:26]

Done.

+          EvaluationResultImpl target = node.getRealTarget().accept(this);
+          return target.stringLength(typeProvider, node);
+        }
+      }
+    }
+    return getConstantValue(node, element);
   }
 
   @Override