Move the bc layer for views UI CSS classes from views to stable9

As predicted, this got lost along the way :) Tagging for D9 readiness

"D9 readiness" isn't an "official" tag. Since this is marked for 9.1, I'm not sure a tag is needed. If it is, it should be "Drupal 9 readiness". Leaving off the tag for now.

This still being in, is now leading to people opening bugs #3391465: Views CSS class is changed when underscores and dashes are mixed, lets see if we can get rid of this

So this just removes the BC layer. I don't see any way to detect that people are using these classes, all we can detect is if we are suppling them with BC classes, so raising a deprecation notice feel weird since it might not be relevant at all.

Would it maybe be sufficient to add a CR with a code snippet that could recreate the BC classes if somebody still needs them?

Something like this seems to do the trick:

function mytheme_preprocess_views_view(&$variables) {
  if (!empty($variables['attributes']['class'])) {
    $bc_classes = preg_replace('/[^a-zA-Z0-9- ]/', '-', $variables['attributes']['class']);
    $variables['attributes']['class'] = array_merge($variables['attributes']['class'], $bc_classes);
  }
  if (!empty($variables['css_class'])) {
    $existing_classes = explode(' ', $variables['css_class']);
    $bc_classes = preg_replace('/[^a-zA-Z0-9- ]/', '-', $existing_classes);
    $variables['css_class'] = implode(' ', array_merge($existing_classes, $bc_classes));
  }
}

Could the issue summary be updated with the proposed solution, "Leave two classes as is." doesn't seem correct anymore.

And you're right not sure how to BC a class removal, and not the first ticket I've seen around this. A CR may be the best thing but even then I imagine if someone is using those removed classes they'll notice when something breaks before the CR.

Updated the IS with the new proposal on how to address this.

I'll ping somebody to see if we can get some more opinions on how to deal with HTML class removal.

Whatever is decided should post here too #2413847: Remove usages of .js class from core

Can we move the BC class to Stable 9? That's the standard approach and allows us to get rid of it once we replace Stable 9.

This may be a dumb question but since the classes are dynamic how do you add those to just stable?

Couldn't we just move the logic from template_preprocess_views_view to stable9_preprocess_views_view?

Yeah that should work, just add that snippet in #17 to stable9

Did what @lauriii suggested. The other case in stable9.theme that seems to have done this didn't get test coverage as far as I can tell, so no test coverage for that for now

Change looks good.

So if this the path forward for any other class removals?

This looks good but we need a change record.

Something like 'Views used to duplicate custom classes like my__class added in the views UI into an additional my--classas a backwards compatibility layer. This backwards compatibility layer has now been moved to the Stable9 theme. If you were relying on these classes, you should either update your CSS to target the correct class, or add Stable9 as a dependency of your theme'

Created a CR from #27.

Made the recommendation to target the correct CSS classes. Do we know how long stable9 will be around? If that should be added to the CR.

I'm triaging RTBC issues. I read the IS and the comments. I didn't find any unanswered questions or other work to do. Although, the proposed resolution is a bit out of date.

Leaving at RTBC.

Committed 3923a9f and pushed to 11.x. Thanks!

Not backporting, so that it'll only be released with D11.