bug#81613: [PATCH] Make vc-dir use display-buffer instead of pop-to-buffer

Hello Juri,

> Date: Thu, 13 Aug 2026 20:57:38 +0300
> 
>> I cannot make it work.
> 
> Actually, there are 3 separate problems here.
> 
> 1. A paren with extra nested level was missing:
> 
>     (setq display-buffer-alist
>           '(((derived-mode . vc-dir-mode)
>              (display-buffer-reuse-mode-window
>               display-buffer-in-tab)
>              (mode . vc-dir-mode))))

Sorry for the mistake! In the original code I was using, the syntax was
correct and after my patch I got it to display in another tab, which is
what I actually want.

>    Maybe we need to create a syntax checker for 'display-buffer-alist'?

If there is that, I am happy to test it and report any bugs.

> 2. But still you can't always match mode in 'display-buffer-alist',
>    because 'vc-dir' enables 'vc-dir-mode' after displaying the buffer
>    for the newly created *vc-dir* buffer.
> 
>    So until 'vc-dir' will be changed to enable
>    'vc-dir-mode' before displaying the buffer,
>    'display-buffer-alist' can reliably match only
>    the buffer name (until a category is added
>    to its 'pop-to-buffer' call):
> 
>     (setq display-buffer-alist
>           '(("\\`\\*vc-dir\\*\\'"
>              (display-buffer-in-tab))))

Oh, I see now why pop-to-buffer is covered by display-buffer-alist. I
was wrong then in thinking that it was not supported.

In the patch I sent, the 'display-buffer' happens after the mode is set.
I assume that is enough for 'display-buffer-alist' to match the buffer
correctly.

So if we want to match 'derived-mode' then my patch should be updated to
use 'pop-to-buffer' instead of 'display-buffer', or is there something 
else?