Use required keys of mappings instead of special casing

Attached is patch for making it work.
The tests also need to be updated to make the config validation happy.

This looks nice & simple! :D

Do you intend to adopt Mapping::getConditionallyValidKeys() in another issue? Or is that planned for this issue?

The annotation of the method I want to use is: Gets all required keys in this mapping. That is exactly what I want.

I don't care which keys are maybe required in a Mapping if it had other data. All I care is the current Mapping with the current data has some required keys and I can use those.

Maybe I should add a test for the case when a key is required in some cases. But the API of getConditionallyValidKeys doesn't seem very useful in this case. I understand it is very useful in error messages.

You're right that the thing that truly matters to Config Split, is only the required keys. 👍

But … that doesn't mean that some config does not have some invalid keys when merging? IOW: I think that #2 is 99% of the value/work, but I do think that the remaining 1% is also important: validating that the result of merging contains only valid keys.

So I was wrong in #3: you indeed do not need to adopt Mapping::getConditionallyValidKeys(). But AFAICT you do need/want Mapping::getValidKeys(). Although perhaps there is something about the way that Config Split is used that you'd need to do some extremely impractical splitting before you could hit that edge case?

Yes you are right of course! getValidKeys would be useful here. But you are also right that this is quite an edge case for config split.

So I prefer not to do anything about the invalid keys now, let core complain about it and the user opening an issue with steps to reproduce it. Then we can investigate why that could happen.

👍

I am postponing this for the core issue to be committed.

📌 Introduce Mapping::getValidKeys(), ::getRequiredKeys() etc. Active has been committed and will ship in 11.3 🚀