Do not apply optimizations based on an element if that element cannot be resolved.

sdk/lib/_internal/compiler/implementation/elements/elements.dart

 // Copyright (c) 2012, 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.
 
 library elements;
 
 import 'dart:uri';
 
 // TODO(ahe): Rename prefix to 'api' when VM bug is fixed.
 import '../../compiler.dart' as api_e;
@@ skipping 102 matching lines @@
   static const ElementKind LABEL =
     const ElementKind('label', ElementCategory.NONE);
   static const ElementKind VOID =
     const ElementKind('void', ElementCategory.NONE);
 
   static const ElementKind AMBIGUOUS =
       const ElementKind('ambiguous', ElementCategory.NONE);
   static const ElementKind ERROR =
       const ElementKind('error', ElementCategory.NONE);
   static const ElementKind MALFORMED_TYPE =
     const ElementKind('malformed', ElementCategory.NONE);

[Johnni Winther, 2013/01/10 07:09:55]

I don't think this kind is used anymore.

[ngeoffray, 2013/01/10 09:41:48]

As discussed, I'll leave it to you or another CL.

+  static const ElementKind UNRESOLVED =

[ahe, 2013/01/09 15:46:27]

Could you use ErroneousElement instead?

[Johnni Winther, 2013/01/10 07:09:55]

ErroneousElement has a different semantics in the backend, namely that a runtime
error should be produced for it. Therefore we need something else.

[ahe, 2013/01/10 07:32:07]

I don't see why. The element is only used by the mock compiler to compare for
identity. We should not add new classes and categories that aren't actually used
in production code.

[Johnni Winther, 2013/01/10 08:19:47]

You are right. I thought it was used by production code.

[ngeoffray, 2013/01/10 09:41:48]

Yes, Done.

+    const ElementKind('unresolved', ElementCategory.NONE);
 
   toString() => id;
 }
 
 class Element implements Spannable {
   static int elementHashCode = 0;
 
   final SourceString name;
   final ElementKind kind;
   final Element enclosingElement;
@@ skipping 288 matching lines @@
 
   getLibrary() => enclosingElement.getLibrary();
 
   String toString() {
     String n = name.slowToString();
     return '<$n: ${messageKind.message(messageArguments)}>';
   }
 }
 
 /**
- * An ambiguous element represent multiple elements accessible by the same name.
+ * An unresolved element represents a selector we did not try to
+ * resolve.
+ */
+class UnresolvedElement extends Element {
+  UnresolvedElement(SourceString name, Element enclosing)
+      : super(name, ElementKind.UNRESOLVED, enclosing);
+}
+
+/**
+ * An ambiguous element represents multiple elements accessible by the same name.

[Johnni Winther, 2013/01/10 07:09:55]

Long line.

[ngeoffray, 2013/01/10 09:41:48]

Done.

  *
  * Ambiguous elements are created during handling of import/export scopes. If an
  * ambiguous element is encountered during resolution a warning/error should be
  * reported.
  */
 class AmbiguousElement extends Element {
   /**
    * The message to report on resolving this element.
    */
   final MessageKind messageKind;
@@ skipping 1712 matching lines @@
 
   MetadataAnnotation ensureResolved(Compiler compiler) {
     if (resolutionState == STATE_NOT_STARTED) {
       compiler.resolver.resolveMetadataAnnotation(this);
     }
     return this;
   }
 
   String toString() => 'MetadataAnnotation($value, $resolutionState)';
 }