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

[Eli Zaretskii <eliz@gnu.org>]

> Cc: juri linkov <juri@linkov.net>
> Date: Fri, 15 Nov 2024 00:29:14 +0200
> From: Dmitry Gutov <dmitry@gutov.dev>
> 
> This adds a capability to customize the destination window selection 
> logic for navigation (xref-find-definitions, xref-go-back, 
> xref-go-forward) by allowing a user-supplied display window function.
> 
> Inspired by the Merlin package and its user option 
> merlin-locate-in-new-window 
> (https://github.com/ocaml/merlin/blob/a36f42a5b181d0c9cc84174e8eb241b11eeabc0f/emacs/merlin.el#L177C12-L177C39) 
> - where the value 'diff' uses a different window if the destination is 
> in an file different from the current one.
> 
> With the attached patch the customization looks a bit noisier though:
> 
>    (setq xref-navigation-display-window-action
>          '(display-buffer-reuse-window))
> 
> ^ This makes it try to reuse an existing window and fall back to 
> pop-to-window, but the effect is similar to what's described above.
> 
> Comments welcome.

I added Martin to the discussion, and have a few minor comments below.

> diff --git a/lisp/progmodes/xref.el b/lisp/progmodes/xref.el
> index cc06e06ef78..670e80ea40b 100644
> --- a/lisp/progmodes/xref.el
> +++ b/lisp/progmodes/xref.el
> @@ -431,6 +431,21 @@ xref-auto-jump-to-first-xref
>    :version "28.1"
>    :package-version '(xref . "1.2.0"))
>  
> +(defcustom xref-navigation-display-window-action nil
> +  "When non-nil, the display action to use for navigation commands.

This is too general, when taken alone (as in the apropos commands).  I
suggest something like

  If non-nil, the `display-buffer' action for showing results of Xref commands.

(The "navigation" part seems misleading, since xref-find-definitions
is not a navigation command.)

> +This does not affect commands that specify the action explicitly,

I guess "...that specify the window to use explicitly" is more
accurate?

> +such as `xref-find-definitions-other-window'."
> +  :type '(choice (const :tag "Use selected window" nil)
> +                 (const :tag "Reuse window showing destination or use another"

I think "If possible, reuse window already showing destination" is
better?

> +(defun xref--switch-to-buffer (buf)
> +  (if xref-navigation-display-window-action
> +      (pop-to-buffer buf xref-navigation-display-window-action)

Should we have some sanity checks for the value of
xref-navigation-display-window-action?  It's a user option, so
theoretically the user could use setq to set it to any value.