[META] Support config actions for using in recipes

I have prepared the first MR for recipe integration https://www.drupal.org/project/search_api/issues/3484304 . It exposes only already existing methods as config actions to start this feature rolling.

This is a good and easy first step, I think that one is ok.

• addDatasource, but at the moment the argument is of type Datasource and it can't be used in recipe. Maybe alternatively there could be a method addDatasourceByIdAndConfig that will have datasource id and its config as arguments.
• setTracker has and object as argument so it can't be used as action method, but maybe having a method setTrackerByIdAndConfig with tracker plugin id and config as arguments would make sense
• The same for setServer it makes sense to create setServerById?
• addProcessor has object as argument, but maybe new method addProcessorByIdAndConfig would be ok to add as well
• addField has Field object as argument, but maybe new method addFieldByFieldConfig would be ok to add

For datasource, and server I think adding a new method is a good idea.
Processors and fields are more difficult, because their configuration can be more extensive, but I guess we can go through the same way here as well?

I think tracker is probably not needed, since for 99% the basic tracker is used. So I'm not sure how I feel about creating this new method, however if we already do this same trick for the other 4 I guess it's not too bad?

Great initiative, thanks! I already merged your first MR, just making existing methods available seems like a low-hanging fruit.

My thoughts on the rest of your suggestions:

• setServerById(): I would just call that setServerId() maybe? Would seem like a natural extension from the existing getServerId(). It’s just a bit unfortunate that getServerInstance() and setServer() don’t follow this sensible pattern.
• addDatasourceByIdAndConfig(): We already added a separate config action plugin for that in #3456728: Create a config action to add a data source to an index. However, if we add new methods for the other plugin types, doing it for datasources would also make sense for the sake of consistency – not sure how to handle that, we probably don’t want to offer two config actions for the exact same thing.
• setTrackerByIdAndConfig(), addProcessorByIdAndConfig(), addFieldByFieldConfig: I admit I first balked a bit at thes suggestions, as I dislike such verbose method names and the methods would pretty much duplicate existing ones. I therefore wanted to suggest instead adding dedicated config action plugins to implement this functionaliy, as we already have for datasources (see above).
  However, on the other hand it does seem a bit strange to have something available to site admins but not to developers. Also, I suspect the DX of those new methods would be better anyways than of the existing ones – I would now say we probably went the wrong way there when first writing the D8 version of the module.
  So, I guess I’m now on board with just adding those methods. I can also imagine our own code subsequently drifting towards using those new methods. They certainly seem handier in most situations. (Though the lack of dependency injection for entities continues to be vexing in this regard.)
  As mentioned above, though, we should think about what to do with datasources. We will probably want to add the addDatasourceByIdAndConfig() method in any case, but maybe just not make it available as a config action?
• setBackend(): This would be a major architectural change as a server’s backend plugin is currently immutable. I would therefore need a very good argument why this would be helpful/needed before considering it.
• setReadOnly(): Yes, good idea. No clue why this is currently missing.

Note that these should all also be added to the interface, in my opinion, which means you’ll have to add them to the UnsavedIndexConfiguration class, too. (Just as a tip, as I regularly forget that as well.)

Methods that are not in Index class yet, but might be useful:

• setServer
• setReadOnly

setServer seems like a typo, as that method already exists (and is listed by you a few lines above). Do you know what you meant?

Two additional action suggestions:

• Index items - with optional data source filtering. Also useful when default content import doesn't trigger indexing automatically - haven't checked to root cause but experienced this when I wrote a test for a recipe
• Assign index to search backend - for recipes that bundle indexes without backends. Should filter by server type (e.g., Solr) with fallback option to prevent exception when a match not found.

I agree with the second one; that sounds useful. The first one however (index items) seems like it shouldn't be happening at all?

Well, I guess the answer is "it depends". Whoever uses that action should be awareof consequences. However without that it is complicated to set up an immediately usable demo env with recipes, where waiting for cron to index items may not be an option.

Created ticket for #3565685: Create a config action to add fields to an index

Would also be useful to have actions to manage data source bundle includes/excludes, and add/remove type-specific boosts.

Consider the example where someone wants to deliver their search configuration and content types in separate recipes:

config:
  actions:
    search_api.index.content:
      addIncludedBundle: landing_page
      addBundleBoost:
        bundle: landing_page
        value: 5.0

Plural variants would be a nice bonus!

@clayfreeman:

Would also be useful to have actions to manage data source bundle includes/excludes, and add/remove type-specific boosts.

That seems a bit too specific to add at this point, when it’s not even possible yet to add fields to an index.

Moreover, I’m not sure how this would work on an architectural level, as the bundle includes/excludes are options specific to the datasource plugin. I don’t think we can/should provide an index-level action to modify these. (Same for the bundle boosts, which is a specific processor plugin.)
Not sure, is there a clean way to provide a config action specific to a certain plugin associated with the entity?