bug#74361: [PATCH] New option xref-navigation-display-window-action

[Juri Linkov <juri@linkov.net>]

>> This option looks similar to 'display-comint-buffer-action'
>> whose addition was deemed to be a mistake, so we needed to declare it
>> obsolete and replace it with '(category . comint)'.
>> So instead of adding 'xref-navigation-display-window-action',
>> could you just add a category 'xref' to xref display function calls?
>> Then users will be able to customize it with e.g.:
>>    (setq display-buffer-alist '(((category . xref)
>>                                  (display-buffer-reuse-window))))
>> Or maybe I misunderstand other requirements for this feature.
>
> Thanks for the comments. The other priority here (I think) seems to retain
> the current behavior by default:
>
> You can see this decision being made in
>
>   (defun xref--switch-to-buffer (buf)
>     (if xref-navigation-display-window-action
>         (pop-to-buffer buf xref-navigation-display-window-action)
>       (switch-to-buffer buf)))
>
> So... I suppose one way to do that would be to add an option in Xref which
> make it use 'pop-to-buffer' instead of 'switch-to-buffer' (similar to
> 'switch-to-buffer-obey-display-actions'). And then the user would customize
> 'display-buffer-alist' like in your example. Something like:
>
>   (setq xref-navigation-obey-display-actions t
>         display-buffer-alist '(((category . xref)
>                                 (display-buffer-reuse-window))))
>
> Is that not too complex, what do we think?

Instead of a new option and 'switch-to-buffer',
a simpler way would be allow the users just to
customize the category with 'display-buffer-same-window':

  (setq display-buffer-alist '(((category . xref)
                                (display-buffer-same-window))))

It works nicely when (category . xref) is added to the same place
like in your patch in 'xref--show-pos-in-buf':

```
diff --git a/lisp/progmodes/xref.el b/lisp/progmodes/xref.el
index cf061a18ee0..0193c2e35e0 100644
--- a/lisp/progmodes/xref.el
+++ b/lisp/progmodes/xref.el
@@ -689,7 +689,7 @@ xref--show-pos-in-buf
                       (eq (window-buffer xref--original-window) buf)))
                  `((xref--display-buffer-in-window)
                    (window . ,xref--original-window))))))
-    (with-selected-window (display-buffer buf action)
+    (with-selected-window (display-buffer buf (append action '((category . xref))))
       (xref--goto-char pos)
       (run-hooks 'xref-after-jump-hook)
       (selected-window))))
```