Error when indexing special fields (search_api_*)

I have an idea why this happens. It comes down to getBackendDefinedFields method in the backend. This is used to expose fixed fields to views, in our case these special fields aren't fixed so they don't have path mapping, and none of them should be available to the view.

I'd personally go with the simplest solution and just return an empty array. Since really these fields can be accessed using other fields. Or we can add fixed fields that map to these. I personally don't see the point in this second solution, but opinions are welcome.

Now we create the fields when calling the getBackendDefiniedFields method. So the error above does not show up and the already existing tests pass. Needs review.

I applied the patch to our site with meilisearch @2.0.0 and the message is gone. No more warnings. Thank you!

I also get "attribute search_api_datasource is not filterable" when I

1. create an index
2. also use "node grants" in the filters (in hope of not indexing e.g. unpublished content)
3. search as an anonymous user

It's hard to tell for me whether this is related? Or shall I raise a separate issue?

Can also confirm that the MR resolves the errors for us, with no obvious side effects.

Merged, thanks.

Automatically closed - issue fixed for 2 weeks with no activity.