Subject: bug#48917: 28.0.50; allow user to choose what function is used when windmove create a window

From: pillule <[email-masked]>
Date: Tue, 08 Jun 2021 16:12:56 +0200

Eli Zaretskii <[email-masked]> writes:

>> From: pillule <[email-masked]>
>> Date: Tue, 08 Jun 2021 12:31:58 +0200
>>
>>  (defcustom windmove-create-window nil
>> -  "Whether movement off the edge of the frame creates a new 
>> window.
>> +  "Whether movement off the edge of the frame creates a new 
>> window or
>> +trigger a custom function.
>
> The first line of a doc string should be a single complete 
> sentence.
> (The reason for this is that some Emacs commands, like "M-x 
> apropos",
> show only the first line of the doc string.)
>
>>  If this variable is set to t, moving left from the leftmost 
>>  window in
>>  a frame will create a new window on the left, and similarly 
>>  for the other
>>  directions."
>> -  :type 'boolean
>> +  :type '(choice (const :tag "Don't create new windows" nil)
>> +          (const :tag "Create new windows" t)
>> +          (function :tag "Provide a function"))
>>    :group 'windmove
>>    :version "27.1")
>
> The :version tag should be updated, because the defcustom was 
> changed.

>From 6438107565875ff69f533c244a9601192218e7c9 Mon Sep 17 00:00:00 2001
From: Trust me I am a doctor <[email-masked]>
Date: Tue, 8 Jun 2021 11:44:54 +0200
Subject: [PATCH] User option to choose a function triggered by windmove-create

* lisp/windmove.el (windmove-create-window): Add a defcustom choice.
(windmove-do-window-select): Trigger custom functions.
---
 lisp/windmove.el | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/lisp/windmove.el b/lisp/windmove.el
index f558903681..d410e387d4 100644
--- a/lisp/windmove.el
+++ b/lisp/windmove.el
@@ -142,13 +142,16 @@ windmove-wrap-around
   :group 'windmove)
 
 (defcustom windmove-create-window nil
-  "Whether movement off the edge of the frame creates a new window.
+  "Whether movement off the edge of the frame create a window.
 If this variable is set to t, moving left from the leftmost window in
 a frame will create a new window on the left, and similarly for the other
-directions."
-  :type 'boolean
-  :group 'windmove
-  :version "27.1")
+directions.
+The variable may also be a function to be called in this circumstance,
+the function should accept as agument a DIRECTION, and the selected WINDOW."
+  :type '(choice (const :tag "Don't create new windows" nil)
+          (const :tag "Create new windows" t)
+          (function :tag "Provide a function"))
+  :version "28.0.50")
 
 ;; If your Emacs sometimes places an empty column between two adjacent
 ;; windows, you may wish to set this delta to 2.
@@ -357,7 +360,9 @@ windmove-do-window-select
                (or (null other-window)
                    (and (window-minibuffer-p other-window)
                         (not (minibuffer-window-active-p other-window)))))
-      (setq other-window (split-window window nil dir)))
+      (setq other-window (if (functionp windmove-create-window)
+                             (funcall windmove-create-window dir window)
+                           (split-window window nil dir))))
     (cond ((null other-window)
            (user-error "No window %s from selected window" dir))
           ((and (window-minibuffer-p other-window)
-- 
2.20.1

--