bug#69993: Wrap window buffers while cycling

[Juri Linkov]

>>> What is the "fixed order"?  When I use C-x b, that buffer becomes the
>>> one most recently shown in that window.
>>
>> The fixed order is similar to how tabs work in web browsers.
>> It would be unexpected when switching to a tab will always
>> move it to the end of the tab line.  This is why it's unexpected
>> for C-x b to move tabs when tab-line-mode is used.
>
> But the lists of previous and next buffers have to reflect the order in
> which these buffers were shown in a window.  You probably  can't map them
> directly to tabs.

They are already mapped to tabs, and users happily used them for 5 years.
The only remaining problem the users complain about is that switching
buffers messes up the order.  There is no problem in using a fixed order
because buffers will be still ordered by the order they were shown in a window.
Only need a way to switch between buffers already shown in a window.

For users of tab-line-mode there is no difference whether to use
'C-x C-left' or 'C-x b' to switch to the previous buffer.

>>> I think 'switch-to-prev-buffer-wrap' already confuses things.  Wrapping,
>>> for me, means to wrap around like when navigating on a ring of buffers.
>>> Whether this should include buffers never shown in the window before is
>>> a different issue IMO.  And whether C-x b should change the order is yet
>>> another issue.  So maybe we need three options instead of one...
>>
>> I can't imagine why anyone would need wrapping when C-x C-left
>> will visit hundreds of buffers never shown in the window.
>
> Emacs "wrapped" in that case ever since (with at least two buffers).

The case of 'emacs -Q' has no practical significance.

>> So we need only two options: wrapping buffers shown in the window,
>> and to keep the fixed order of C-x b.  So I will create a new request
>> for the fixed order of C-x b.  And here is the final patch for wrapping:
>
> I still don't agree with it.  IMHO we have to cater for two cases:
>
> (1) The classic behavior where switching may show a buffer never shown
>     in the window before.  I suppose you mean that
>     'switch-to-prev-buffer-wrap' does not affect it.  If that's the
>     case, please say so.

Indeed, 'switch-to-prev-buffer-wrap' does not affect it.
Switching to a buffer that was never shown in the window
should still reset the list of next-buffers to nil.

> (2) The new behavior where switching may only show buffers shown in that
>     window before.  For this you want to either wrap or not.  So the
>     option 'switch-to-prev-buffer-wrap' will affect (2) only.  Right?

'switch-to-prev-buffer-wrap' will affect only 'C-x C-left' and 'C-x C-right'
cycling buffers shown in that window before.