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]

On 2015-06-22, at 12:28, Marcin Borkowski <mbork@mbork.pl> wrote:

> On 2015-06-22, at 12:19, Marcin Borkowski <mbork@mbork.pl> wrote:
>
>> Hello,
>>
>> today I found that fill-single-char-nobreak-p is just a bit too
>> simplistic.  When point is after e.g. the string " (a", it returns nil
>> instead of t.  I am not sure which characters should be added to the
>> regex, but at least the opening paren (and maybe bracket) should be
>> there, so I'd change the regex into [[:space:]][[(]*[[:alpha:]].  (Two
>> or more opening parens/brackets are unlikely, but when in doubt, I guess
>> it's better to return t than nil than the other way round.)
>>
>> Best regards,
>
> Just noticed that there is a hardcoded (backward-char 2), so it
> seems that adding a few characters to the regex is not enough.  Maybe
> looking-back is the way to go (though it might slow filling down)?
> I don't know.

Hi there,

so here's a patch for the bug I reported some time ago.  Please review
both the patch and the commit message (I'm still learning to write
them...).

Best,

-- 
Marcin

>From de6c196235ef8abfff52c9cfc3d97a6350e8a5a7 Mon Sep 17 00:00:00 2001
From: Marcin Borkowski <mbork@mbork.pl>
Date: Sun, 17 Apr 2016 08:30:49 +0200
Subject: [PATCH] Fix `fill-single-char-nobreak-p'

* lisp/textmodes/fill.el (fill-single-char-nobreak-p): make space after
        opening paren and a single-letter word unbreakable (Bug#20871)
---
 lisp/textmodes/fill.el | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/lisp/textmodes/fill.el b/lisp/textmodes/fill.el
index 173d1c9..bade8fa 100644
--- a/lisp/textmodes/fill.el
+++ b/lisp/textmodes/fill.el
@@ -337,7 +337,10 @@ fill-single-char-nobreak-p
   (save-excursion
     (skip-chars-backward " \t")
     (backward-char 2)
-    (looking-at "[[:space:]][[:alpha:]]")))
+    (or (looking-at "[[:space:]][[:alpha:]]")
+        (progn
+          (backward-char 1)
+          (looking-at "[[:space:]]([[:alpha:]]")))))
 
 (defcustom fill-nobreak-predicate nil
   "List of predicates for recognizing places not to break a line.
-- 
2.4.3