Deprecate $variables['teaser']

Nice idea but tests are failed, so there's usage to clean-up

The deprecation process of theme-template-stuff is not very clear, (at least to me): https://www.drupal.org/about/core/policies/core-change-policies/drupal-d... → .

Looks like the current deprecation message isn't added to the ['node']['variables'] return of node_theme(), but instead is overwriting it, leaving all node-theming logic without the actual node. Hence the gazillion test-failures.

If I look here, we can only deprecate the root level itself and not anything specific below it? https://git.drupalcode.org/project/drupal/-/blob/11.x/core/lib/Drupal/Co...

If I use that option for this issue, we're getting a deprecation warning _every_ time node_theme() is used.
We _could_ ignore that deprecation warning in core/.deprecation-ignore.txt, but maybe this would be the time to introduce deprecation at lower levels of theming functions return arrays?

@Spokje I think deprecating in node_theme() if variables was already in the definition might have been OK, but rather than figure that out, I moved the deprecation to template_preprocess_node() next to where the variable is actually set, which seems like a better place for it anyway.

We have one usage of this in Olivero which I updated in the MR. This shows the limitations of the deprecation because unless we made $variables an ArrayAccess object, we can't trigger anything when it's referenced in preprocess - but this will only be removed in a major update so I think it's OK to do the best we can for now. Maybe a follow-up for $variables as ArrayAccess is worth exploring.

Nice, this even detected the sole usage in Olivero, so I'm more than happy to RTBC this.

I've decided not to create any follow-ups, since this shows we have a working solution for this case and I'm against Death-By-Admin, but if anyone wants to fill out templates and create a new issue, I'm all for it.

Nice, this even detected the sole usage in Olivero

This isn't entirely true. The first version of the MR I removed the setting of $variables['teaser] altogether, which was wrong (it needs to stay in and be deprecated), and that broke Olivero which checks bool instead of empty. If I hadn't made the mistake, the Olivero usage wouldn't have been picked up. However the only way we can do that is to trigger a deprecation error when an array key is accessed and the only way I can think of to do that is $variables as ArrayAccess. Maybe we can do that in a follow-up but it shouldn't block IMO, otherwise we can never deprecate anything in preprocess ever.

Committed b2109b4 and pushed to 11.x. Thanks!

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