List plugin will merge lists that are not the same

[mlewand]

📝 Provide detailed reproduction steps (if any)

Currently list plugin's converters (during downcasting) will consider lists the same as long as they have: same tag name and classes.

See:

ckeditor5/packages/ckeditor5-list/src/utils.js

Lines 175 to 183 in caca54b

	if ( !firstList || !secondList || ( firstList.name != 'ul' && firstList.name != 'ol' ) ) {
	return null;
	}
	// Both parameters are list elements, so compare types now.
	if ( firstList.name != secondList.name || firstList.getAttribute( 'class' ) !== secondList.getAttribute( 'class' ) ) {
	return null;
	}

And combine both lists.

Lists could be as well differentiated by different attributes. For instance, per spec, ordered list can contain ol type (values like a, I or 1 denote numbering type, though it can be done by CSS too). With this logic two different lists will be merged.

Also developer might use custom data- attribute to semantically differentiate some lists type.

For instance I saw one CKEditor 5 implementation where there were 3 list types (numbered, bulleted and third). Third type was merged with bulleted as it was downcasted to ol[type] and it was considered to be same as plain ol which caused bug.

📃 Other details

• Browser: Any
• OS: Any
• First affected CKEditor version: 24.0.0 (didin't check earlier but surely it's here for a longer time)

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[mlewand]

I pushed a i/8829 branch where I verified that adding attribute check solves the problem.

However, there are 11 failing unit test in list style so there's probably a need to accommodate for the fix in list style plugin too.

[dunx]

This remains an issue 2 years on from the last update. Is there another issue anybody is aware of?
We have a client that has CKE4 markup with two very different styled lists next to each other and they are arbitrarily being merged by CKE5.

[star-szr]

Is there another issue anybody is aware of?

See #14478, more recently the AdjacentListsSupport plugin has been added that somewhat handles this use case. See #14944 for a known issue with regard to nested lists.

[Witoso]

Yes, thank you @star-szr, let's close it as a duplicate, this is resolved viaAdjacentListsSupport, and we need to fix #14944.