bug#71727: Deleting TAGS buffer will cause `etags-regen--update-file` doesn't work

[Dmitry Gutov <dmitry@gutov.dev>]

Hi again!

On 29/06/2024 14:49, Siyuan Chen wrote:
>  > Is there are particular reason you killed the TAGS buffer?
> 
> No. I found this bug is just because I tried to view the TAGS content 
> while editing a .c file and then closed it (I am using tab-line-mode 
> with tab-line-close-tab-function set to kill-buffer). Since then, I have 
> stopped closing the TAGS buffer.

Thanks for the clarification.

> Another option is to temporarily add documentation advising users not to 
> close the TAGS buffer, because closing it accidentally can result in the 
> odd behavior.

I think actually a simpler approach can suffice: using kill-buffer-hook 
in the TAGS buffer. Like this:

diff --git a/lisp/progmodes/etags-regen.el b/lisp/progmodes/etags-regen.el
index dc778b14061..21ea9bfb8b3 100644
--- a/lisp/progmodes/etags-regen.el
+++ b/lisp/progmodes/etags-regen.el
@@ -294,7 +294,9 @@ etags-regen--visit-table
    (add-hook 'before-save-hook #'etags-regen--mark-as-new)
    (setq etags-regen--tags-file tags-file
          etags-regen--tags-root root)
-  (visit-tags-table etags-regen--tags-file))
+  (visit-tags-table etags-regen--tags-file)
+  (with-current-buffer (get-file-buffer tags-file)
+    (add-hook 'kill-buffer-hook #'etags-regen--tags-cleanup nil t)))

  (defun etags-regen--ctags-p ()
    (string-search "Ctags"
@@ -390,7 +392,8 @@ etags-regen--mark-as-new

  (defun etags-regen--tags-cleanup ()
    (when etags-regen--tags-file
-    (let ((buffer (get-file-buffer etags-regen--tags-file)))
+    (let ((buffer (get-file-buffer etags-regen--tags-file))
+          kill-buffer-hook)
        (and buffer
             (kill-buffer buffer)))
      (tags-reset-tags-tables)