desugarAssignment_(lvalue, rvalue) {
    let tempId = createIdentifierExpression(this.addTempVar());
    let desugaring = new AssignmentExpressionDesugaring(tempId);
    this.desugarPattern_(desugaring, lvalue);
    return desugaring.createAssignmentExpression(tempId, rvalue);
  }
@param {ParseTree} lvalue
@param {ParseTree} rvalue
@return {ParseTree}