bug#32651: flyspell marks doublons when not the same case

[Reuben Thomas <rrt@sc3d.org>]

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On 7 September 2018 at 10:49, Reuben Thomas <rrt@sc3d.org> wrote:

> On 7 September 2018 at 06:59, Eli Zaretskii <eliz@gnu.org> wrote:
>
>>
>> I'm not claiming the current behavior is a good default, I'm saying it
>> is there for a long time, and thus takes precedence, because we cannot
>> possibly poll all those users who see that behavior every day and none
>> of them complained.
>>
>> This is why I suggested a new customizable option: that way, you and
>> anyone else who wants Flyspell to behave differently can have that,
>> and if we learn this is the preferred behavior (by getting requests to
>> set that as default), we can make it the default at some future point.
>> IOW, what I suggested is a path towards potentially changing the
>> default, but gradually and without backward incompatibilities.  OK?
>>
>
> OK!
>
Attached, a patch. If the code's OK, I can write a NEWS entry (anything
else?).

-- 
https://rrt.sc3d.org

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diff --git a/lisp/textmodes/flyspell.el b/lisp/textmodes/flyspell.el
index 4d7a18969e..cf209abf6a 100644
--- a/lisp/textmodes/flyspell.el
+++ b/lisp/textmodes/flyspell.el
@@ -68,6 +68,11 @@ flyspell-mark-duplications-flag
   :group 'flyspell
   :type 'boolean)
 
+(defcustom flyspell-case-fold-duplications t
+  "Non-nil means Flyspell matches duplicate words case-insensitively."
+  :group 'flyspell
+  :type 'boolean)
+
 (defcustom flyspell-mark-duplications-exceptions
   '((nil . ("that" "had")) ; Common defaults for English.
     ("\\`francais" . ("nous" "vous")))
@@ -1150,7 +1155,8 @@ flyspell-word
 			      (- (save-excursion
                                    (skip-chars-backward " \t\n\f")))))
 			  (p (when (>= bound (point-min))
-			       (flyspell-word-search-backward word bound t))))
+			       (flyspell-word-search-backward
+                                word bound flyspell-case-fold-duplications))))
 		     (and p (/= p start)))))
 	    ;; yes, this is a doublon
 	    (flyspell-highlight-incorrect-region start end 'doublon)