bug#17758: 24.3; The line isn't wrapped during printing if it contains non ascii chars

[Eli Zaretskii <eliz@gnu.org>]

> From: Lars Ingebrigtsen <larsi@gnus.org>
> Date: Sat, 29 May 2021 07:38:15 +0200
> Cc: 17758@debbugs.gnu.org
> 
> (defun ps-mule-plot-string (from to &optional _bg-color)
> [...]
> 	 (ascii-or-latin-1 "[\000-\377]+")
> [...]
> 	    ((looking-at ascii-or-latin-1)
> 	     (let ((nchars (- (min (match-end 0) stop) (point))))
> 	       (setq width (* average-width nchars))
> 	       (if (< ps-width-remaining (+ run-width width))
> 		   (setq nchars (truncate (- ps-width-remaining run-width)
> 					  average-width)
> 			 run-width (+ run-width (* nchars average-width))
> 			 endpos (+ (point) nchars))
> 		 (setq run-width (+ run-width width))
> 		 (forward-char nchars))))
> 
> 	    (t
> 	     (while (and (< (point) stop) (not endpos))
> 	       (setq width (char-width (following-char)))
> 	       (if (< ps-width-remaining (+ run-width width))
> 		   (setq endpos (point))
> 		 (setq run-width (+ run-width width))
> 		 (forward-char 1))))))
> 
> This is trying to do word line wrapping if we're looking at ASCII or
> Latin-1 text.  (I'm not sure I understand the reasoning behind that, but
> perhaps it's because we don't want to wrap (say) Chinese text?  But...
> what's so special about Latin-1?  Why not fold Cyrillic?)
> 
> Anyway, the regexp is buggy, why is why this doesn't work.  I've now
> fixed this in Emacs 28.

I'm not sure I understand the fix, can you explain it?

Regarding the reason for limiting ourselves to Latin-1: AFAIR, ps-mule
doesn't support non-ASCII characters outside Latin-1 and CJK character
sets.  Perhaps this is the reason for this code?  But the only expert
on this is Handa-san (CC'ed): perhaps he could help us understand what
the code is doing?