Proposed patch: ignore show-paren-mode fails in comments

[Oleh Krehel <ohwoeowho@gmail.com>]

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Hi all,

I like to have `show-paren-mode' in my Lisp buffers. However, it will
fail to match the parens in commented multi-line expressions like this
one:

;; =>
;; (0
;;  (1
;;   (2
;;    (3 (4 (5 (6 (7 (8 (9 ()))))))))))

I attach a patch to ignore these failures.


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From 91ba1c3dee055ac4617445b944f28af63408f90c Mon Sep 17 00:00:00 2001
From: Oleh Krehel <ohwoeowho@gmail.com>
Date: Tue, 8 Sep 2015 16:04:06 +0200
Subject: [PATCH] lisp/paren.el (show-paren--default): Ignore fails in comments

---
 lisp/paren.el | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/lisp/paren.el b/lisp/paren.el
index 30314c2..adf2849 100644
--- a/lisp/paren.el
+++ b/lisp/paren.el
@@ -210,7 +210,9 @@ Where HERE-BEG..HERE-END is expected to be near point.")
 	;; If found a "matching" paren, see if it is the right
 	;; kind of paren to match the one we started at.
 	(if (not (integerp pos))
-	    (if mismatch (list here-beg here-end nil nil t))
+	    (if mismatch
+                (unless (nth 4 (syntax-ppss))
+                  (list here-beg here-end nil nil t)))
 	  (let ((beg (min pos outside)) (end (max pos outside)))
 	    (unless (eq (syntax-class (syntax-after beg)) 8)
 	      (setq mismatch
-- 
2.5.1


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Interestingly, as I pasted the code into this `message-mode' buffer,
`show-paren-mode' doesn't fail any more, since ";;" don't register as
comments any more. Maybe `scan-sexps' could be modified to scan
differently (i.e. ignoring comments) if the starting position is in a
comment. This would be preferable to just ignoring the scan errors like
the attached patch does.

What do you think?

    Oleh