bug#9286: fill-paragraph destroys URLs

[Chong Yidong <cyd@stupidchicken.com>]

If I am decoding the jidanni-speak correctly, his complaint is doing M-q
on a buffer containing

asdf
國

turns the text into

asdf國

instead of what he wants:

asdf 國


This is because line joining does not include a space if *either*
character on each side of the newline has the ?| (line-breakable)
category and an entry in fill-nospace-between-words-table.  To get the
behavior jidanni wants, we could change it so that *both* the characters
must have this property; see attached patch.

But I am not sure this is TRT in general.  Handa-san, could you weigh in
with an opinion?  Adding a space seems more or less correct to me, but I
am no expert.


*** lisp/textmodes/fill.el	2011-07-16 20:05:54 +0000
--- lisp/textmodes/fill.el	2011-08-20 19:52:41 +0000
***************
*** 482,491 ****
  	    (replace-match (get-text-property (match-beginning 0) 'fill-space))
  	  (let ((prev (char-before (match-beginning 0)))
  		(next (following-char)))
! 	    (if (and (or (aref (char-category-set next) ?|)
! 			 (aref (char-category-set prev) ?|))
! 		     (or (aref fill-nospace-between-words-table next)
! 			 (aref fill-nospace-between-words-table prev)))
  		(delete-char -1))))))
  
    (goto-char from)
--- 482,491 ----
  	    (replace-match (get-text-property (match-beginning 0) 'fill-space))
  	  (let ((prev (char-before (match-beginning 0)))
  		(next (following-char)))
! 	    (if (and (aref (char-category-set next) ?|)
! 		     (aref (char-category-set prev) ?|)
! 		     (aref fill-nospace-between-words-table next)
! 		     (aref fill-nospace-between-words-table prev))
  		(delete-char -1))))))
  
    (goto-char from)