bug#33992: 27.0.50; xref-find-definitions wastes too much space

[Juri Linkov]

>> The problem with xref-find-definitions is its unexpected outcome:
>> sometimes it pops up a window, sometimes doesn't.
>
> Imagine the process of code completion.
>
> Sometimes you press TAB (or C-M-i) and it completes to the symbol you
> wanted. Sometimes it pops up a window with all matching
> completions instead.
>
> Does it feel the same way to you?

The difference is that completions pop up in a small unobtrusive window.
But this should be easy to do in xref now too.

Thanks to João, we now have configurable window management in xref,
so I tried different customizations, and one of the most appealing
is this:

  (defun display-buffer-condition-xref (buffer-name _action)
    (and (string-match-p "\\`\\*\\(xref\\)\\*\\(\\|<[0-9]+>\\)\\'"
                         buffer-name)
         (memq this-command '(xref-find-definitions))))

  (defun display-buffer-condition-from-xref (_buffer-name _action)
    (string-match-p "\\`\\*\\(xref\\)\\*\\(\\|<[0-9]+>\\)\\'"
                    (buffer-name (current-buffer))))

  (setq display-buffer-alist
     '((display-buffer-condition-xref
        display-buffer-in-direction
       (direction . below) (window-height . fit-window-to-buffer))))

  (with-eval-after-load 'xref
    (define-key xref--button-map [(control ?m)] #'xref-quit-and-goto-xref))

How do you like that?