bug#20871: 25.0.50; fill-single-char-nobreak-p does not recognize a single-letter word when it is preceded by an open paren

[Marcin Borkowski <mbork@mbork.pl>]

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On 2016-04-17, at 16:49, Eli Zaretskii <eliz@gnu.org> wrote:

>> From: Marcin Borkowski <mbork@mbork.pl>
>> Cc: 20871@debbugs.gnu.org
>> Date: Sun, 17 Apr 2016 17:34:04 +0200
>> 
>> In Polish typography, it is customary to foribid line breaks after
>> one-letter words (and we have quite a few of them: a, i, o, w, z - they
>> are conjunctions or prepositions).  And it is not uncommon to have
>> a combination of them with a parenthesized remark or something like
>> that.  That's why allowing a linebreak after, say "(a" when writing
>> something in Polish (like an email, for instance) is a bug IMO.
>> 
>> > See, the function in question, fill-single-char-nobreak-p, is
>> > documented as a possible value to use in the fill hook, for a very
>> > specific purpose.  If you are saying that it doesn't fulfill that
>> > purpose well enough, please show a use case where it fails to do that.
>> > At least the situation you described, with " (a", doesn't seem to fit
>> > the use cases which this function is supposed to cover, since the
>> > parenthesis makes a 2-character sequence, whereas
>> > fill-single-char-nobreak-p aims to support isolated one-character
>> > words.
>> 
>> I see.  So you suggest that instead of patching
>> `fill-single-char-nobreak-p' I should have provided another function,
>> customized for Polish?
>
> Yes, I think so.  There's already fill-french-nobreak-p, why shouldn't
> there be a Polish predicate?

I attach a new patch. Is it better now?

Best,

-- 
Marcin Borkowski
http://octd.wmi.amu.edu.pl/en/Marcin_Borkowski
Faculty of Mathematics and Computer Science
Adam Mickiewicz University

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From 6356c46bf6d5c90057b1a756f05c69791c9ff3db Mon Sep 17 00:00:00 2001
From: Marcin Borkowski <mbork@mbork.pl>
Date: Wed, 27 Apr 2016 08:59:15 +0200
Subject: [PATCH] Add the function `fill-polish-nobreak-p'

* lisp/textmodes/fill.el (fill-polish-nobreak-p): Prevent line-breaking
after a single-letter word even if this word is not preceded by
a space.  (Bug #20871)
---
 lisp/textmodes/fill.el | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/lisp/textmodes/fill.el b/lisp/textmodes/fill.el
index 173d1c9..0a95290 100644
--- a/lisp/textmodes/fill.el
+++ b/lisp/textmodes/fill.el
@@ -329,6 +329,18 @@ fill-french-nobreak-p
 	      (and (memq (preceding-char) '(?\t ?\s))
 		   (eq (char-syntax (following-char)) ?w)))))))
 
+(defun fill-polish-nobreak-p ()
+  "Return nil if Polish style allows breaking the line at point.
+This function may be used in the `fill-nobreak-predicate' hook.
+It is almost the same as `fill-single-char-nobreak-p', with the
+exception that it does not require the one-letter word to be
+preceded by a space.  This blocks line-breaking in cases like
+\"(a jednak)\"."
+  (save-excursion
+    (skip-chars-backward " \t")
+    (backward-char 2)
+    (looking-at "[^[:alpha:]][[:alpha:]]")))
+
 (defun fill-single-char-nobreak-p ()
   "Return non-nil if a one-letter word is before point.
 This function is suitable for adding to the hook `fill-nobreak-predicate',
-- 
2.4.3