[css-text-3] Define break at space to remove a space explicitly

[fantasai]

We currently assume that the rules about trimming white space at the end of a line takes care of disappearing a space at which we break the text.

However, this isn't quite the case when there's bidi, see web-platform-tests/wpt#5461

We should define that for collapsible spaces, if the line-break opportunity taken is provided by that space, it is removed.

This is what makes sense (otherwise you'd end up with double spaces frequently in bidirectional text), and is also what seems to have been implemented.

[kojiishi]

Is it reasonable to do bidi-reordering after phase 2? The behavior would then be defined as desired, correct?

[frivoal]

In effect yes, although only for collapsible spaces. We can't hang non collapsible spaces that have been bidi-reordered to the middle of the line.

All browsers today do collapse/remove collapsible space that would have been at the end of the line prior to bidi reordering (AFAIK Edge&IE used to be different, as discussed in web-platform-tests/wpt#5461), so this change/clarification is safe:
https://jsbin.com/zepovaj/edit?html,css,output

[frivoal]

Actually, a little more testing shows that there's less interop than I thought:
https://jsbin.com/hijucaq/edit?html,css,output

Chrome	Firefox	Safari	Edge 18

I think the behavior of Chrome and Firefox is preferable.

[fantasai]

@frivoal, this issue is only about collapsible spaces. If there's an issue about preserved spaces, can you file a separate issue? Otherwise it becomes too confusing for everyone to discuss.

[frivoal]

Sure, I'll split. I reported this here as it seemed to me that these are related problems, and that neither is clearly defined, and I discovered the inconsistency of pre-wrap while investigating normal, so it made sense to me to discuss them as a set, but keeping issues tightly scoped is useful.

[frivoal]

Edited in place my earlier comment to remove things that were not about collapsible spaces, and moved that content over to #4422

[css-meeting-bot]

The CSS Working Group just discussed Define break at space to remove a space explicitly, and agreed to the following:

• RESOLVED: Space before a line break is removed even if reordered to the middle of line by bidi reordering

The full IRC log of that discussion

<dael> Topic: Define break at space to remove a space explicitly
<dael> github: https://github.com//issues/4308
<dael> florian: Turns out that it isn't exactly defined or interop impl what happens with interaction of dropping collapsible whitespace and bidi. If somethign would have been at the end of bidi moves it do you still drop it? Fuzzily defined. Chrome and FF do one thing, Safari and Edge HTML is different. I think Chrome/FF makes more sense. Screenshots in the issue
<dael> florian: I propose we adopt Chrome/FF behavior and task editors to define it
<dael> myles: Webkit would be willing to change
<dael> Rossen_: Edge HTML this could be considered. It's reasonable behavior
<dael> florian: Prop: Adopt the Chrome/FF behavior and action the editors to spec it
<dael> Rossen_: Can you be more specific?
<dael> fantasai: Spec before a line break is removed even if reorder to middle of line by bidi reordering
<dael> s/spec/space
<dael> RESOLVED: Space before a line break is removed even if reordered to the middle of line by bidi reordering