Views RSS view mode settings are completely broken

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This blocks 📌 Add validation constraints to all system.* simple config (except system.rss) Needs work and 🌱 [meta] Add constraints to all simple configuration Active .

Pushed to a MR with some small changes.

Upgrade path is tested afaik, so removing that tag. Has tests it seems, so removing that tag also. Did small update to IS, but don't see how we can make this more clear.

This will need a CR though. Dont think we need to deprecate anything really, since this is pretty much broken functionality you cant rely on.

Added a change record.

All tests are green. Which is great.

Not sure about the upgrade path. I'll ask around

Any existing views that have default as the RSS view mode need to be updated so they store whatever the default value actually was, before we delete that value from config.

Little more context; https://drupal.slack.com/archives/C079NQPQUEN/p1744791038514039

Well, seems i have a working test. While going through the motions i did find a one more view that use default still.

views.view.taxonomy_term.yml

      row:
        type: node_rss
        options:
          relationship: none
          view_mode: default

Also a little confused. If i look at system.rss.yml the default should be rss i think, since that was in the config. But when running the update test it gets set to title, i really don't understand how that is possible. What am i missing there?

fixed tests, so setting to NR

Left a couple of (reasonably horrible) questions on the MR.

Responded to @catch's review, NW for these changes.

I've got some questions about your approach, there might be more gotcha's (and possibly a bug :P)

Still need to handle 2 things:

1. When default is the viewmode, and we have no config this will keep updateing to the first key. Oops.
2. Run this noSave

Now running on onSave in the updateAll method.

Also added an extra check for when we have no reference from system.rss and there is an available view_mode called default.