A hack which finds the index of the current calling script.

script_current.gml

/// @desc Returns the id of the current script.
/// @author Kat @katsaii
var callstack = debug_get_callstack();
var header = "gml_Script_";
var delimiter = ":";
for (var i = 1; i < array_length_1d(callstack); i++) {
    var currentTrace = callstack[i];
    if (string_pos(header, currentTrace) == 1) {
        var name = string_replace(currentTrace, header, "");
        var length = string_pos(delimiter, name);
        if (length > 0) then name = string_copy(name, 1, length - 1);
        if (asset_get_type(name) == asset_script) then
                return asset_get_index(name);
    }
}
return -1;