[11.x] Remove the CKEditor 4 upgrade path

#3194084: Support functionality equivalent to ckeditor_stylesheets added an additional thing to be deleted in Drupal 11.

@xjm You've rescoped this issue to be for Drupal 10, even though it was originally for Drupal 11. Even in the roadmap (#3238333: Roadmap to CKEditor 5 stable in Drupal 9), it says: Obsoleteness of upgrade path in Drupal 11.

Rescoping. The code shouldn't be deleted; it should be simply moved to the CKEditor 4 module, which in turn gets moved to contrib.

That does not make sense: the CKEditor 4 module cannot provide an upgrade path for CKEditor 5 because:

• SmartDefaultSettings is also used to compute smart default settings for text formats using either no text editor or a text editor other than CKE4 — as described in #3226673: API addition: \Drupal\editor\Plugin\EditorPluginInterface::getDefaultSettings() should accept old Editor + Format to generate smart defaults, that's always a valuable capability to have, and is sorely missing for CKEditor 4 today.
• and therefore we'd need to have the CKEditor 5 module provide some sort of pluggable API to allow parts of SmartDefaultSettings (the CKEditor 4-specific bits, see previous point: not everything in that class is related to CKEditor 4!) to live in a separate module

So, created #3270831: Make the CKEditor 4 → 5 upgrade path work even when the CKEditor 4 module is removed for this new scope.

👍

Meanwhile, #3270831: Make the CKEditor 4 → 5 upgrade path work even when the CKEditor 4 module is removed is now ready for review — good news: managed to make it work with net less code than before 🤓🥳

This sort of ties into #3304736: Provide a good UX to ensure the CKEditor 4 to 5 update is always done before upgrading to Drupal 10 unless the contrib module is installed — if the upgrade to Drupal 10 and CKEditor 5 is required to do before the update to Drupal 10, we can actually just remove the upgrade path in Drupal 10.

Except … that https://www.drupal.org/project/ckeditor is around, which allows CKEditor 4 to exist on Drupal 10. So I think that means the original outline (removing this in late 2023/early 2024) is still accurate.

Moving to 10.1.x. I'd move it to a further release if I could 🤓

>14 months have passed since #11: it's now late 2023, tomorrow is December 1!

https://www.drupal.org/project/ckeditor will be unsupported soon.

Time to start exploring our options.

Very interesting, I sort of expected this to not happen 😅 Then again, sites can't go from Drupal 9 to 11 directly (i.e. no bypassing start Drupal 10), so … it makes sense to do this.

It triggers … Feels 😅 to be removing this — I spent a lot of time building this. And I built it for clean ejection when it was no longer needed, which is NOW, so it does feel kinda satisfying (cathartic?) to see how nicely this is removing ~1250 LoC (and more soon) 🤩

MR reviewed — I explained which other test cases (which you already alluded to, @quietone!) that are safe to remove can be identified 😊

Failing on PHPStan:

  139    Parameter $stylesheets_message of method                             
         Drupal\ckeditor5\Plugin\Editor\CKEditor5::__construct() has invalid  
         type Drupal\ckeditor5\CKEditor5StylesheetsMessage.                   

Simple fix fortunately: that is just no longer necessary :)

10.3 has been branched. Does that mean this can land now? It's unlikely the affected will change in 10.3 too, so it's also unlikely that this'll make MRs more difficult to land?

Merged in upstream changes. Then finished what @quietone started: removed all traces of CKEditor5StylesheetsMessage.

The test cases in SmartDefaultSettingsTest are now almost all stale/irrelevant: they're specifically testing an update from CKEditor 4, and that's no longer necessary.

Because going forward, SmartDefaultSettings can and will only look at the HTML restrictions of the text format. Will tackle that next.

https://git.drupalcode.org/project/drupal/-/merge_requests/6329/diffs?co... got us down to 2 failing tests: SmartDefaultSettingsTest as predicted in #27, plus \Drupal\Tests\ckeditor5\FunctionalJavascript\CKEditor5AllowedTagsTest::testSwitchToVersion5().

I just pushed a commit that should make the latter pass, the commit message explains how/why.

I recommend reviewing the test coverage changes using

Only two <code>@todo

s are left. This is 98% ready.

And now it will be green! 😄 Whew, this was quite a lot of work: to keep the good parts of SmartDefaultSettings that are still relevant now that CKEditor 4 is gone.

Bumping to Major given the diffstat of +367, −1731.

Shoot!

Merged in latest 11.x.

The failure is reproducible locally:

TypeError: Cannot read properties of null (reading 'length')
    at Object._parseSetting (http://localhost/subdirectory/core/modules/filter/filter.filter_html.admin.js?v=11.0-dev:310:39)
    at http://localhost/subdirectory/core/modules/filter/filter.filter_html.admin.js?v=11.0-dev:95:30
    at Array.forEach (<anonymous>)
    at Object.attach (http://localhost/subdirectory/core/modules/filter/filter.filter_html.admin.js?v=11.0-dev:90:9)
    at http://localhost/subdirectory/core/misc/drupal.js?v=11.0-dev:166:24
    at Array.forEach (<anonymous>)
    at Drupal.attachBehaviors (http://localhost/subdirectory/core/misc/drupal.js?v=11.0-dev:162:34)
    at http://localhost/subdirectory/core/misc/drupal.init.js?v=11.0-dev:32:12
    at HTMLDocument.listener 

… but it'd be solved automatically by #2567801: Deprecate core/modules/editor/js/editor.admin.js JS APIs in Drupal 10, for removal in Drupal 11.

#2567801: Deprecate core/modules/editor/js/editor.admin.js JS APIs in Drupal 10, for removal in Drupal 11 landed!

All green! 😄 🥳

90% of this MR is trivial.

The 10% that is non-trivial is in SmartDefaultSettings. For it to continue to work (to provide default settings based on HTML restrictions of a text format, which 99% of the time means based on filter_html configuration), a few additions were necessary.

You might question the need for that. Why:

1. It makes it easy for existing text formats to adopt CKEditor 5
2. It minimizes the changes to SmartDefaultSettingsTest