How to debug error in process sentinel?

Question

I've recently switched to doom emacs, and for the most part it's working great.

However, when I'm looking at a folder in dired-mode, if I copy a file using C the file is copied but *Messages* contains the following:

error in process sentinel: vc-exec-after: Unexpected process state
error in process sentinel: Unexpected process state No library
simple.el in search path

More significant is that it leaves a .git/index.lock which I need to manually delete.

I have the following questions:

1. How can this issue be investigated?
2. How can this specific issue be fixed?
3. How can the 'vc' aspect of dired be disabled?

The last point is because I would like to use magit exclusively.

Answer 1

With regard to 1., I'm not sure about Doom Emacs, but on GNU Emacs you could navigate to lisp/vc/vc-dispatcher.el, move pointer to (defun vc-exec-after (code) ... and invoke C-u C-M-x to invoke eval-defun. Move cursor to first line, add a breakpoint edebug-set-breakpoint, and run the code/command again to use Edebug to step through the code.

Also, maybe you can get a hint from invoking toggle-debug-on-error. It should show a minibuffer with error and stack trace when errors occur anywhere in the elisp code paths.

Answer 2

With regard to 3, there is a variable that specifies a list of backends to ignore:

Documentation

VC backends to ignore.

The directories registered to one of these backends won't have status indicators.

Adding the following in .doom.d/config.el adds Git to the list of ignored backends:

(after! dired
  (setq diff-hl-dired-ignored-backends (append
                                        '((Git) (RCS)))))