Issue 3540. Better error message for string concatenation

compiler/java/com/google/dart/compiler/ast/DartBinaryExpression.java

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file

[Brian Wilkerson, 2012/06/14 15:20:52]

nit: copyright year

 // 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.
 
 package com.google.dart.compiler.ast;
 
 import com.google.dart.compiler.parser.Token;
 import com.google.dart.compiler.resolver.Element;
 import com.google.dart.compiler.resolver.MethodNodeElement;
 
 /**
  * Represents a Dart binary expression.
  */
 public class DartBinaryExpression extends DartExpression {
 
   private final Token op;
+  private final int opOffset;
   private DartExpression arg1;
   private DartExpression arg2;
   private MethodNodeElement element;
 
-  public DartBinaryExpression(Token op, DartExpression arg1, DartExpression arg2) {
+  public DartBinaryExpression(Token op, int opOffset, DartExpression arg1, DartExpression arg2) {
+    this.opOffset = opOffset;
     assert op.isBinaryOperator() : op;
 
     this.op = op;
     this.arg1 = becomeParentOf(arg1 != null ? arg1 : new DartSyntheticErrorExpression());
     this.arg2 = becomeParentOf(arg2 != null ? arg2 : new DartSyntheticErrorExpression());
   }
 
   public DartExpression getArg1() {
     return arg1;
   }
 
   public DartExpression getArg2() {
     return arg2;
   }
 
   public Token getOperator() {
     return op;
   }
+  
+  /**
+   * @return the character offset of the {@link #getOperator()} token.
+   */
+  public int getOperatorOffset() {
+    return opOffset;
+  }
 
   @Override
   public void visitChildren(ASTVisitor<?> visitor) {
     arg1.accept(visitor);
     arg2.accept(visitor);
   }
 
   @Override
   public <R> R accept(ASTVisitor<R> visitor) {
     return visitor.visitBinaryExpression(this);
   }
 
   @Override
   public MethodNodeElement getElement() {
     return element;
   }
 
   @Override
   public void setElement(Element element) {
     this.element = (MethodNodeElement) element;
   }
 }