bug#71605: 30.0.50; [PATCH] Support variable-width text in 'visual-wrap-prefix-mode'

[Jim Porter <jporterbugs@gmail.com>]

On 6/17/2024 12:55 PM, Eli Zaretskii wrote:
>> Cc: 71605@debbugs.gnu.org
>> Date: Mon, 17 Jun 2024 11:17:45 -0700
>> From: Jim Porter <jporterbugs@gmail.com>
>>
>> Replacing :align-to with :width works just fine though. It's entirely
>> possible I'm just doing something wrong, but maybe this is a bug?
> 
> It's a bug in Emacs 29 and Emacs 30.  It works in Emacs 27.

Ah, that explains it.

>> (Now what would be great is if :align-to supported a *string* value that
>> meant "use the pixel-width of this string".
> 
> It's already possible: just have a variable that holds the width, and
> use it in the :align-to expression.

That would make the code simpler, but I'd still need to figure out when 
to reevaluate the variable to update things.

>> Which actually gives me an
>> idea... what if the wrap-prefix is just the original text like "* " and
>> we fontify it to be invisible? It's not part of the buffer and you can't
>> select it anyway, so it doesn't really matter what the text is so long
>> as it's not visible.)
> 
> I don't think I follow: how is this relevant to the issue at hand?

I was thinking you could wrap "* this is some text" like so:

   * this is
   * some text

The second "* " would come from the wrap-prefix, but we'd make the 
foreground transparent (or the same color as the background) so it 
wouldn't be visible. Then it would always take up the same width as the 
first "* " because it's the same string with the same font and everything.