anchor.diff:          voidContext));
     }
   
  +  /// Returns an [Expression] representing a pre-increment or pre-decrement
  +  /// of the accessor.
     Expression buildPrefixIncrement(Name binaryOperator,
         {bool voidContext: false, Procedure interfaceTarget}) {
       return buildCompoundAssignment(binaryOperator, new IntLiteral(1),
           voidContext: voidContext, interfaceTarget: interfaceTarget);
     }
   
  +  /// Returns an [Expression] representing a post-increment or post-decrement
  +  /// of the accessor.
     Expression buildPostfixIncrement(Name binaryOperator,
         {bool voidContext: false, Procedure interfaceTarget}) {
       if (voidContext) {
  
positive.code:     return _finish(_makeSimpleWrite(value, voidContext));
    }
  
    Expression buildNullAwareAssignment(Expression value, DartType type,
        {bool voidContext: false}) {
      if (voidContext) {
  
negative.code: 
  import 'package:kernel/ast.dart';
  
  /// An [Accessor] represents a subexpression for which we can't yet build a
  /// kernel [Expression] because we don't yet know the context in which it is
  /// used.
  ///
  /// Once the context is known, an [Accessor] can be converted into an
  /// [Expression] by calling a "build" method.
  ///
  /// For example, when building a kernel representation for `a[x] = b`, after
  /// parsing `a[x]` but before parsing `= b`, we don't yet know whether to
  /// generate an invocation of `operator[]` or `operator[]=`, so we generate an
  /// [Accessor] object.  Later, after `= b` is parsed, [buildAssignment] will be
  /// called.
  abstract class Accessor {
    /// Builds an [Expression] representing a read from the accessor.
    Expression buildSimpleRead() {
      return _finish(_makeSimpleRead());
    }
  
    /// Builds an [Expression] representing an assignment with the accessor on
    /// the LHS and [value] on the RHS.
    ///
    /// The returned expression evaluates to the assigned value, unless
    /// [voidContext] is true, in which case it may evaluate to anything.
  