Eeeeh it's probably me, because somewhere else:

\PHPStan\dumpType($this->organization->sites()->getQuery()); // 🟩 Illuminate\Database\Eloquent\Builder<App\Models\Site>

It still knows about Site.

Maybe because my SiteCheck is also a generic, and my Organization::site_checks() doesn't specify that (because it doesn't know the specific):

// No @return here
public function site_checks() : Relations\HasManyThrough {
	return $this->hasManyThrough(SiteCheck::class, Site::class, 'organization_id', 'site_id');
}

But if I add a @return with the generic (Checked is still generic, because no idea which type it returns):

/** @return Relations\HasManyThrough<SiteCheck<Checked>> */
public function site_checks() : Relations\HasManyThrough {
	return $this->hasManyThrough(SiteCheck::class, Site::class, 'organization_id', 'site_id');
}

phpstan complains about its return value:

Method Organization::site_checks() should return Relations\HasManyThrough<SiteCheck<Checked>> but returns Relations\HasManyThrough<SiteCheck>.

because yeah kinda, because hasManyThrough() doesn't know about a potential generic. Is that Larastan's fault, because it doesn't take potential generics into account? How do I fix this?

And with that @return the original problem holds: getQuery() loses the generic type SiteCheck.

Wow, generics are a lot of trouble with phpstan level 5+. Suddenly argument.type errors everywhere. Like these:

Parameter #1 $query of static method Watchlist::getChecks() expects Builder<SiteCheck<Checked>>, Builder<SiteCheck> given.

Come ooon! That's good enough!

Use the wildcard if you're not sure / don't care what the inner types will be:

/** @return Relations\HasManyThrough<SiteCheck<*>> */
public function site_checks() : Relations\HasManyThrough {
	return $this->hasManyThrough(SiteCheck::class, Site::class, 'organization_id', 'site_id');
}

That's good to know, but that doesn't solve any part of the problem. getQuery() still returns EloquentBuilder<EloquentModel> instead of EloquentBuilder<SiteCheck> (or even with generic: EloquentBuilder<SiteCheck<*>>). I think Larastan doesn't support generics in relationship return types. That's why sites() works (Site is not a generic), but site_checks() doesn't (SiteCheck is a generic). I think. The @return in

/** @return Relations\HasManyThrough<SiteCheck<*>> */
public function site_checks() : Relations\HasManyThrough {
	return $this->hasManyThrough(SiteCheck::class, Site::class, 'organization_id', 'site_id');
}

doesn't do/change anything. Larastan makes the return type Relations\HasManyThrough<SiteCheck> anyway. And then the generic is lost. And then getQuery() fails its own generic. Or something. I don't know Phpstan well enough.

If I hack Larastan's ModelRelationsDynamicMethodReturnTypeExtension to skip Organization::site_checks() Phpstan will use the @return, and the first dumpType 'works':

Relations\HasManyThrough<SiteCheck<*>>

But that still doesn't fix the getQuery() type:

EloquentBuilder<EloquentModel>

It's still the base Model! Why doesn't it use SiteCheck or SiteCheck<*> ??

I'll take a look. Is that the only relation or does it do that for all relation types?

Omg I'm an idiot. Site also has a relationship to SiteCheck, and it works perfectly there. The problem isn't that SiteCheck is a generic, but the HasManyThrough relationship! Another through-relationship somewhere else has the same problem:

\PHPStan\dumpType($contact->sites()); // 🟩 Relations\HasManyThrough<Site>
\PHPStan\dumpType($contact->sites()->getQuery()); // 🟥 EloquentBuilder<EloquentModel>

Site is not a generic, but sites() is a HasManyThrough. That is the problem. I still don't know why, but that's progress 😆

@rudiedirkx Could you try the latest 2.x branch? It seems to be fixed cause I can't reproduce it.