I think there is no support in moodle repository window for making combo box in repository window. Under repository folder file name call javascript.php line 452 in version 1.65 code below is written for making text type input box in repository window box.
}else if(data[k].type=='textarea') {
str += '<p><textarea id="'+data[k].id+'" name="'+data[k].name+'"></textarea></p>';
}
But if I need combo box support I mean selecting type in repository window box; there is no code for it. So I suggest below code need to will apply in javascript.php file for developer to give him ability to make comb box type selecting. Following line should be added after above line code
else if(data[k].type=='select') {
str += '<p><label>'+data[k].labelname+':</label><select id="'+data[k].id+'" name="'+data[k].name+'">'+data[k].option+'</select></p>';
}
//Zahid