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

> 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))))

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

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))))

3. To disable the effect of selecting the window
with the vc-dir buffer by 'pop-to-buffer', it's possible
to use 'post-command-select-window':

    (setq display-buffer-alist
          '(("\\`\\*vc-dir\\*\\'"
             (display-buffer-below-selected)
             (post-command-select-window . nil))))