bug#66431: [PATCH] Fix reset treesit--explorer-last-node when explorer buffer was killed

[Yuan Fu <casouri@gmail.com>]

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> On Oct 14, 2023, at 9:20 PM, nvp <noah.v.peart@gmail.com> wrote:
> 
> Hi,
> The patch is supposed to reset `treesit--explorer-last-node` in the source buffer, just before the `(with-current-buffer treesit--explorer-buffer ...)`.
> Upon trying to reproduce it now, I realized it's harder to reproduce than I had thought -- sorry about that.  
> I noticed the bug (if it is a bug) initially when I was adding a function to jump b/w source and explorer buffers, like the following:
> 
> (defun my-treesit-explorer-jump ()
>   "Pop b/w source and explorer buffers."
>   (interactive)
>   (let ((buf
>          (cond
>           ((eq major-mode 'treesit--explorer-tree-mode)
>            (when (buffer-live-p treesit--explorer-source-buffer)
>              treesit--explorer-source-buffer))
>           (t
>            (unless (and treesit-explore-mode
>                         (buffer-live-p treesit--explorer-buffer))
>              ;; *** Without the reset here, the explorer buffer doesn't
>              ;; get redrawn the first time, when treesit--explorer-last-node
>              ;; is non-nil in the source buffer ***
>              ;; (setq-local treesit--explorer-last-node nil)
>              (cl-letf (((symbol-function (function completing-read))
>                         (lambda (&rest _) (symbol-name (treesit-language-at (point))))))
>                (treesit-explore-mode 1)))
>            treesit--explorer-buffer))))
>     (pop-to-buffer buf)))
> 
> Let me give a more precise recipe to reproduce:
> 1. From a c++-ts-mode buffer, call `treesit-explorer-mode`, select `cpp`.  Now there should be an explorer buffer.
> 2. Kill the associated explorer buffer.
> 3. Now, back in the c++-ts-mode buffer, `treesit--explorer-last-node` should still have a value.
> 4. From that c++-ts-mode buffer, call `my-treesit-explorer-jump`, and the explorer buffer should be empty, until
> switching back to the source buffer.
> 
> This seems to me to be caused by `treesit--explorer-post-command` not running until the source 
> buffer is active again.

Thank you, I think I see the problem now. Could you try the below patch and see it fixes your problem? Also, sorry for the late reply, I meant to reply sooner but couldn’t find the time to figure out what exact was the cause :-) I was initially a bit confused since we already do set last-node to nil.

Yuan


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diff --git a/lisp/treesit.el b/lisp/treesit.el
index c73ac9912d6..9f7e8bacd35 100644
--- a/lisp/treesit.el
+++ b/lisp/treesit.el
@@ -3198,13 +3198,13 @@ treesit-explore-mode
               (treesit--explorer-tree-mode)))
           (display-buffer treesit--explorer-buffer
                           (cons nil '((inhibit-same-window . t))))
+          (setq-local treesit--explorer-last-node nil)
           (treesit--explorer-refresh)
           ;; Set up variables and hooks.
           (add-hook 'post-command-hook
                     #'treesit--explorer-post-command 0 t)
           (add-hook 'kill-buffer-hook
                     #'treesit--explorer-kill-explorer-buffer 0 t)
-          (setq-local treesit--explorer-last-node nil)
           ;; Tell `desktop-save' to not save explorer buffers.
           (when (boundp 'desktop-modes-not-to-save)
             (unless (memq 'treesit--explorer-tree-mode

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