bug#69993: Wrap window buffers while cycling

[Juri Linkov]

>>>> So keeping the stable order of window prev/next buffers after C-x b
>>>> with a hook should be implemented in tab-line.el, not in window.el?
>>>
>>> I don't know how you currently handle C-x <left>, C-x b or
>>> 'rename-buffer' or whether a buffer is modified on the tab line so I
>>> can't tell whether you would need a hook for these.  But this issue is
>>> IMHO not connected to whether getting the previous or next buffer should
>>> wrap or be restricted to buffers previously shown in a window.
>>
>> Handling 'C-x b' and 'rename-buffer' is not yet implemented.
>> Probably need to add a new window parameter to keep a list
>> of tab buffers and sync it with window prev/next buffers.
>
> Now handling 'C-x b' is completely implemented here:
>
> +    (set-window-prev-buffers
> ...
> +      (add-hook 'window-buffer-change-functions #'tab-line-buffer-change nil 
> t)

Actually using hooks as well as advices in core packages is not a nice
thing to do.  Neither tab-bar.el nor tab-line.el uses hooks and advices.
Also better not to mess with set-window-prev-buffers.  And this is
perfectly possible with the following small patch that supports
everything: wrapping, C-x <left>, C-x b, 'rename-buffer' with
buffers restricted to those that were displayed in the window
while keeping them in the fixed order:

diff --git a/lisp/tab-line.el b/lisp/tab-line.el
index 54e9ee16243..b2f0cbf13ed 100644
--- a/lisp/tab-line.el
+++ b/lisp/tab-line.el
@@ -345,6 +345,8 @@ tab-line-tabs-function
 grouped by `tab-line-tabs-buffer-group-function'."
   :type '(choice (const :tag "Window buffers"
                         tab-line-tabs-window-buffers)
+                 (const :tag "Window buffers with fixed order"
+                        tab-line-tabs-fixed-window-buffers)
                  (const :tag "Same mode buffers"
                         tab-line-tabs-mode-buffers)
                  (const :tag "Grouped buffers"
@@ -515,6 +524,17 @@ tab-line-tabs-window-buffers
             (list buffer)
             next-buffers)))
 
+(defun tab-line-tabs-fixed-window-buffers ()
+  "Like `tab-line-tabs-window-buffers' but keep stable sorting order."
+  (let ((old-buffers (window-parameter nil 'tab-line-fixed-window-buffers))
+        (new-buffers (tab-line-tabs-window-buffers)))
+    (setq new-buffers (sort new-buffers
+                            (lambda (a b)
+                              (> (length (memq a old-buffers))
+                                 (length (memq b old-buffers))))))
+    (set-window-parameter nil 'tab-line-fixed-window-buffers new-buffers)
+    new-buffers))