emacs-lisp-mode-hook: Enable xref-etags-mode inside Git repos

This makes it easier to jump to definitions in the repository rather
than definitions for symbols defined in the current Emacs session.
Aside from needing to generate a TAGS file, the tradeoff is that I
have to use describe-variable or {find,describe}-function for symbols
outside of repo.

1 files changed, 10 insertions, 0 deletions

diff --git a/init.el b/init.el
index 26a0b2b..da48d8a 100644
--- a/init.el
+++ b/init.el
@@ -1875,6 +1875,16 @@
     (setq outline-level #'km/elisp-outline-level))
   (add-hook 'emacs-lisp-mode-hook #'km/elisp-set-outline-vars)
 
+  (defun km/elisp-use-xref-etags-inside-git ()
+    (when (and (executable-find "git")
+               (equal (with-temp-buffer
+                        (call-process "git" nil t nil
+                                      "rev-parse" "--is-inside-work-tree")
+                        (buffer-string))
+                      "true\n"))
+      (xref-etags-mode 1)))
+  (add-hook 'emacs-lisp-mode-hook #'km/elisp-use-xref-etags-inside-git)
+
   ;; Modified from usepackage's issue #80.
   (defun km/imenu-add-use-package ()
     (when (string= (buffer-file-name (buffer-base-buffer))