On Sun, Nov 27, 2022 at 9:29 AM Juanma Barranquero <lekktu@gmail.com> wrote:
>
> This works, for example:
>
> (defun xref--add-log-current-defun ()
>   (if-let (item (xref--item-at-point))
>       (xref-file-location-file (xref-match-item-location item))
>     (xref--imenu-extract-index-name)))
>
> (setq-local add-log-current-defun-function #'xref--add-log-current-defun)

In fact, to respect the value of `xref-file-name-display' (which seems a
good idea) a bit more complexity is required:

(defun xref--add-log-current-defun ()
  "Return the string used to group a set of locations.
This function is used as a value for `add-log-current-defun-function'."
  (xref--group-name-for-display
   (if-let (item (xref--item-at-point))
       (xref-location-group (xref-match-item-location item))
     (xref--imenu-extract-index-name))
   (xref--project-root (project-current))))

but that uncovers a different bug in xref--group-name-for-display:

   (cl-ecase xref-file-name-display
     (abs group)
     (nondirectory
      (if (string-match-p "\\`~?/" group)
          (file-name-nondirectory group)
        group))

that is, for the 'nondirectory case it tries to match against ~/filename or
/filename, but (again) ignores absolute Windows paths with a drive letter.

That should be changed to

   (cl-ecase xref-file-name-display
     (abs group)
     (nondirectory
-     (if (string-match-p "\\`~?/" group)
+     (if (string-match-p "\\`\\(~\\|[A-Za-z]:\\)?/" group)
          (file-name-nondirectory group)
        group))
     (project-relative

or something similar.