Add processor to show parents in hierarchical facets

I tested the patch on Facets 3.0, and it worked, but I had to make some changes. I had to implement the supportsFacet() method to work properly with facets_exposed_filters.
I’ll create a fork soon.

I assumed this new processor should only work with taxonomy terms, so I added the same check used in TermWeightWidgetOrderProcessor. To avoid duplicating code, I encapsulated the logic into a trait and updated that class to use it as well.

This is how it is rendered in filter settings.

IMHO this is a bug report, and when enabled is the expected behavior.

I've been pulling my hair out over this, trying to work out why the term hierarchy is not shown, only for it to be a problem with the module.

Thank you for this fix!

This works great, once you set the processors to the correct order, e.g.:
* Show parents
* URL handler
* Transform entity ID to label
* Build hierarchy tree

Marking RTBC to get the maintainer to take a look.

On a local barebones 11.1.x install with the latest Facets 3.0.x I could not reproduce the problem that this resolves.

We might need to dig into it a little more and add test coverage to confirm exactly what behavior we're after, because I wonder how much of it is a data problem?

On a website I'm using this with I'm seeing some unexpected behavior where terms are being placed under incorrect parent items. For example, I have one term which does not have a parent in the database, but it is placed under a term which isn't even in the vocabulary that the first term comes from.

I set up a new sandbox and was able to identify what was missing in the original one.
It turns out the Index hierarchy processor wasn’t enabled on the site where I encountered the issue.

I'm not sure if the ShowParents processor is still needed.