Fix for Issue 622

frog/gen.dart

 // Copyright (c) 2011, 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.
 
 /**
  * Top level generator object for writing code and keeping track of
  * dependencies.
  *
  * Should have two compilation models, but only one implemented so far.
  *
@@ skipping 1820 matching lines @@
     }
 
     // TODO(jimhug): The usual battle with making assign impl not look ugly.
     if (xn is VarExpression) {
       return _visitVarAssign(kind, xn, yn, position, captureOriginal);
     } else if (xn is IndexExpression) {
       return _visitIndexAssign(kind, xn, yn, position, captureOriginal);
     } else if (xn is DotExpression) {
       return _visitDotAssign(kind, xn, yn, position, captureOriginal);
     } else {
-      world.error('illegal lhs', position.span);
+      world.error('illegal lhs', xn.span);
     }
   }
 
   // TODO(jmesserly): it'd be nice if we didn't have to deal directly with
   // MemberSets here and in visitVarExpression.
   _visitVarAssign(int kind, VarExpression xn, Expression yn, Node position,
       Value captureOriginal(Value right)) {
     final name = xn.name.name;
 
     // First check in block scopes.
@@ skipping 594 matching lines @@
       result.add(new Value(world.varType, '\$$i', null, /*needsTemp:*/false));
     }
     for (int i = bareCount; i < length; i++) {
       var name = getName(i);
       if (name == null) name = '\$$i';
       result.add(new Value(world.varType, name, null, /*needsTemp:*/false));
     }
     return new Arguments(nodes, result);
   }
 }