CKE5 and contrib: better "next action" description on upgrade path messages

After deeper analyze of the subject, I noticed they are various types of messages that can be generated during the process. Therefore I had to take an opiniated decision on how to handle them as status, warning or error. The decision here is taken as follow:

• success for messages when Drupal took an action that results in fixing the functionality or migrate it properly to CKE5.
• warning for messages when Drupal took a decision resulting in a functionality drop that can be fixed by direct manual action (no module update, or other) and / or that might work anyway, for instance a button removed that might actually have an inlined equivalent within CKE5.
• error for messages when we know Drupal action resulted in a loss of functionality.

Here is an exhaustive list of the message types and how I considered them.

Status messages :

• The following plugins were enabled to support tags that are allowed by this text format: %enabling_message_content.
• The following tags were permitted by this format's filter configuration, but no plugin was available that supports them. To ensure the tags remain supported by this text format, the following were added to the Source Editing plugin's Manually editable HTML tags: @unsupported_string.
• The following plugins were enabled to support specific attributes that are allowed by this text format: %enabled_for_attributes_message_content.
• This format's HTML filters includes plugins that support the following tags, but not some of their attributes. To ensure these attributes remain supported by this text format, the following were added to the Source Editing plugin's Manually editable HTML tags: @missing_attributes.

Warning messages :

• The CKEditor 4 button %button does not have a known upgrade path. If it allowed editing markup, then you can do so now through the Source Editing functionality.

Error messages :

• The %cke4_plugin_id plugin settings do not have a known upgrade path.

This would be an expected result following this rule :

Before example :

After example :

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As of the subject of a message pointing to a listing documentation by @ifrik at #4, I personally like it in the theory, however I can't figure out a practical way to list all those module and to maintain this list up-to-date as of who would have such a responsibility ?

Added a commit to do what's explained in #8 and see.
Tests are left untouched and therefore expected to fail at this point.

Tests changed to reflect the message structure change and verify the desired message types.

Now passes the tests and PHPCS

Sure, I forgot about that part, let's cross with @wim-leers or @laurii about this.

@ifrik I should provide a patch for the other branches I suppose indeed.

Meanwhile pushing in the PR an additionnal message as suggested at #14 with a wording provided by @ifrik:

Check this handbook page for details about compability issues of contrib modules.

Adding patches for your convenience for the 3 branches. It a bit of a pain to maintain them three. Should it be ? Or working on D10 is enough ?

Nice work @andregp ! That lets the last test to pass (at least with the 9.3.x patch, I have to check about what's wrong with that failure on the 10.0.x branch).

If I may though, in term of keeping the tests consistant : you changed the array merge of $basic_html_test_case['expected_messages'] by reimplementing the strings which is different than any other tests in file. They where updated by keeping the merge and making it array_merge_recursive because the new depth of the array. You can see that in action for a reference in other tests by search at the following:
'expected_messages' => array_merge_recursive($basic_html_test_case['expected_messages'], [

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This should stick with the pattern of merging with $basic_html_test_case['expected_messages'] as per others tests consistancy. It alo avoids duplicating strings in case of update in the future.

+++ b/core/modules/ckeditor5/tests/src/Kernel/SmartDefaultSettingsTest.php
@@ -568,10 +581,13 @@ public function provider() {
-        $basic_html_test_case['expected_messages'],
...
+      'expected_messages' => [

Adding image on "after" the patch as described in #8 : let me update that comment become image was lost.

Updated patch at #24 with feedback from #27.

Updated before / after screenshots :

Before:

After:

NOTE1: we can see the various WARNING / ERROR messages types as decided, as well as the link to the handbook warning message.
NOTE2: the messages themselves may be reworked as part of #3245967: Messages upon switching to CKEditor 5 are overwhelming but it is out of scope of the current issue.

I said this in-person at the DDD sprints, but I lost track of it — sorry! 😅

Totally correct. And I also lost it in the way ! I will update the patch when I have time for it (or anyone can do actually :p).

Hopefully I did not introduce any new errors here and every behave as expected.
Here is an updated screenshot of the result :

Damn, I did not pull before the patch indeed ! This issue is trolling us !
Here is the updated 41 patch with tests pass.