how to fix this HH FIXME [4410]?

Question

Trying to fix a HH complain... Basically the code is doing something similar to this

Sfirstgroup = idx($largegroup, "first");

$final_thing = null

if(HH\is_any_array(Sfirstgroup) && Sfirstgroup){

   /*HH_FIXME[4110] Error revealed by is_arry refining to varray_or_darray */

   $final_thing = idx(Sfirstgroup[0],"final_thing")

}

I think it must have some thing to with firstgroup[0] doesn't have a collection type. but couldn't figure out how to fix this...

Thanks a lot!

Answer 1

You have two type errors:

1. Indexing with square bracket syntax $firstgroup[0] doesn't work very well with the inferred type from is_any_array, which infers wildcard generics for the key type (i.e. it's a KeyedContainer<_,_>). Either change $a[0] to idx($a, 0) or use is_vec_or_varray if all your keys are int, since it refines to vec<_>.
2. You need to prove $firstgroup[0] is a KeyedContainer to use your second idx call for $final_thing. The refinement checks like is_any_array won't work on an indexed variable (like $firstgroup[0]), so you have to make a temporary variable to refine it.

All in all, here's one possible solution:

$firstgroup = idx($largegroup, "first");

$final_thing = null;

if(HH\is_vec_or_varray($firstgroup)){
    $first_item = $firstgroup[0];
    if(HH\is_any_array($first_item)) {
        $final_thing = idx($first_item,"final_thing");
    }
}