Should covariance be added to Builder::with?

[vixducis]

In commit 2f83567, more advanced types were added to Builder::with. More specifically:

/**
 * Set the relationships that should be eager loaded.
 *
 * @param  array<array-key, array|(\Closure(\Illuminate\Database\Eloquent\Relations\Relation<*,*,*>): mixed)|string>|string  $relations
 * @param  (\Closure(\Illuminate\Database\Eloquent\Relations\Relation<*,*,*>): mixed)|string|null  $callback
 * @return $this
 */
public function with($relations, $callback = null) {}

These new types pose an issue for my existing codebase, with larastan on high levels. An example:

Module::query()->with(['preferences' => fn (HasMany $q) => $q->whereBelongsTo($user)]);

Currently, this is incompatible with Builder::with, because the function definition is invariant. Changing HasMany to Relation also breaks, because whereBelongsTo is not available on Relation. While I agree this is technically correct, laravel also tightly couples the relation name and it's type. If I follow the current types I would have to check the type of relation each time:

Module::query()->with(['preferences' => function(Relation $qry) {
    if (false === $qry instance HasMany) {
        throw new Exception('Invalid relation type');
    }
    $q->whereBelongsTo($user);
});

This not only is very tedious, but laravel will already throw if I supply the wrong relation type. The situation could also be easily solved by making the Relation type covariant:

/**
 * Set the relationships that should be eager loaded.
 *
 * @param  array<array-key, array|(\Closure(\Illuminate\Database\Eloquent\Relations\Relation<*,*,*>): mixed)|string>|string  $relations
 * @param  (\Closure(\Illuminate\Database\Eloquent\Relations\Relation<*,*,*>): mixed)|string|null  $callback
 * @return $this
 */

Thoughts?

[vixducis]

This apparently isn't possible yet: phpstan/phpstan#11707.
Closing this is that might solve the issue there.