bug#65896: 30.0.50; folding text with text properties prevents background from extending past the newline

[StrawberryTea]

Sure. Basically, I want :extend to apply to a line with a folded region even
though the newline at the end itself does not have the :extend property. So I
want the extend property to somehow propagate across a line to the newline at
the end, even if it does not have the :extend property. This would allow for
:extend to work as expected when we have a a folded region that extends across
multiple lines but the end of the folded region does not have the :extend
property.

I don’t think this would cause unexpected behavior since :extend on non-newline
characters is currently a no-op.

Eli Zaretskii <eliz@gnu.org> writes:

>> From: StrawberryTea <look@strawberrytea.xyz>
>> Cc: juri@linkov.net, kevin.legouguec@gmail.com, 65896@debbugs.gnu.org,
>>  yantar92@posteo.net
>> Date: Sat, 30 Sep 2023 17:55:27 -0500
>>
>> Basically, when the text is folded, it uses the face of the first visible
>> newline after the fold to determine the background.
>>
>> The elisp approach is to maintain overlays at the end of each folded region 
>> and
>> it becomes complicated with nested headings. I was thinking that instead, we
>> could have the extend property (or an extra option on :extend) be used within
>> the line to colorize the background of the newline at the end.
>
> Sorry, I still don’t understand what you mean by the last sentence.
> (All the rest is understood, but it describes the current situation,
> which I understand well enough to not need any explanations.)