[Webkit-unassigned] [Bug 247481] white-space: break-spaces seems to collapse or hang spaces after element boundaries

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=247481

--- Comment #1 from zalan <zalan at apple.com> ---
(In reply to Andreu Botella from comment #0)
> Created attachment 463398 [details]
> Test case for this bug
> 
> The `white-space: break-spaces` CSS property should not hang or collapse
> spaces, and should only allow breaking after spaces rather than before them.
> But it seems like in Webkit, in some cases an element boundary before a
> space can collapse or hang the space, even when that element does not change
> the `white-space` property with respect to its parent.
> 
> In the attachment test, notice that there is no space at the start of the
> second line before "BB", which means either the space after "AAAA"
> overflowed, or it collapsed or hanged. However, "C " is allowed to overflow
> and doesn't here, so the space does not seem to be considered for
> line-breaking purposes, when it should.
> 
> This is an issue considered for the "web compat" part of Interop 2023
> (https://github.com/web-platform-tests/interop/issues/187), which was
> initially reported as a bug in Chromium before I noticed Webkit also has a
> related bug.
Thanks for filing this issue. I looked at the compat bug (https://codepen.io/kizu/pen/mdMEOvw) and it renders fine on trunk WebKit (see attached screenshot). The attached test case renders the same in all browsers (see attached screenshot) so I am a bit puzzled of what the compat issue here is.
first line: "AAAA "
second line: "BB "
third line: "C D" 
(in both cases)

first line: we break _at_ the first soft wrap opportunity which is _after_ the preserved white space and yes, it overflows the block container's content box.
second line: we see "BB C" fit the line and proceed to the next "character" and find the white space.
Now since there's no soft wrap opportunity between "C" and " ", we either 
1. proceed further and include the trailing white space and produce a line of "BB C " or 
2. revert to the last wrap opportunity (_after_ the first white space) and produce a line of "BB ".
We choose the latter and break _after_ the preserved white space (no overflow here).
third line: fits as is.

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