Diagnose illegal lvalues better.

dart/sdk/lib/_internal/compiler/implementation/scanner/listener.dart

Index: dart/sdk/lib/_internal/compiler/implementation/scanner/listener.dart
diff --git a/dart/sdk/lib/_internal/compiler/implementation/scanner/listener.dart b/dart/sdk/lib/_internal/compiler/implementation/scanner/listener.dart
index 687cec8ea120da5f7377f3b3130f692ef6d4fa79..ac001450cf8bae784a51407d94472efe0b883965 100644
--- a/dart/sdk/lib/_internal/compiler/implementation/scanner/listener.dart
+++ b/dart/sdk/lib/_internal/compiler/implementation/scanner/listener.dart
@@ -1369,8 +1369,11 @@ class NodeListener extends ElementListener {
     Node arg = popNode();
     Node node = popNode();
     Send send = node.asSend();
-    if (send == null) internalError(node: node);
-    if (!(send.isPropertyAccess || send.isIndex)) internalError(node: send);
+    if (send == null || !(send.isPropertyAccess || send.isIndex)) {
+      // TODO(ahe): The parser should diagnose this problem, not this
+      // listener.
+      listener.cancel('Syntax error: Not assignable.', node: node);
+    }
     if (send.asSendSet() != null) internalError(node: send);
     NodeList arguments;
     if (send.isIndex) {
@@ -1817,8 +1820,8 @@ class NodeListener extends ElementListener {
 
   void internalError({Token token, Node node}) {
     // TODO(ahe): This should call listener.internalError.
-    listener.cancel('internal error', token: token, node: node);
-    throw 'internal error';
+    Spannable spannable = (token == null) ? node : token;
+    throw new SpannableAssertionFailure(spannable, 'internal error in parser');
   }
 }