improve debugging

[progfolio]

Alternatively, we could add some kind of "bug report" command, but that's a later problem.

Originally posted by @Stebalien in https://github.com/emacs-exwm/exwm/issues/43#issuecomment-2138355135

[progfolio]

From a quick glance it seems like many of the calls to exwm--log are inserted as the first form in a function and do not make use of any arguments. We could replace these calls by introducing a global-minor-mode, e.g. exwm-debug-mode, which adds before advice to exwm's functions and calls exwm--log.

That should take care of 107 of the 254 instances of exwm--log in the code base.

One alteration this approach would require is modifying xcb-debug:compile-time-function-name, since the forms would no longer be present at compile time. We should be able to get the same information at run time. I've done something similar in Elpaca:

(defun elpaca--caller-name (n &rest skip)
  "Return Nth calling function's name, skipping symbols in SKIP."
  (cl-loop with current = (backtrace-frame (1+ n)) ;; Skip this function call.
           with previous = nil
           while (and (or (not (eq (car current) t))
                          (memq (cadr current) skip))
                      (setq previous current current (backtrace-frame (cl-incf n))))
           finally return (cadr (or current previous))))

Which produces the Continued by: lines in Elpaca's logs:

log:
  [2024-05-30 08:12:16] Package queued
  [2024-05-30 08:12:16] Continued by: elpaca--process
  [2024-05-30 08:12:16] Queueing Dependencies
  [2024-05-30 08:12:16] Continued by: elpaca--check-status
  [2024-05-30 08:12:16] Unblocked by: xelb
  [2024-05-30 08:12:16] No Info dir file found
  [2024-05-30 08:12:16] Continued by: elpaca--add-info-path
  [2024-05-30 08:12:16] Activating package
  [2024-05-30 08:12:16] Package build dir added to load-path
  [2024-05-30 08:12:16] Caching autoloads
  [2024-05-30 08:12:16] Autoloads cached
  [2024-05-30 08:12:16] Continued by: elpaca--activate-package
  [2024-05-30 08:12:16] ✓ 0.001 secs

EDIT: I see now we already have an exwm-debug global minor mode. It's just a matter of altering it to use the advice approach.

[medranocalvo]

Improvements to debugging are very welcome. In my experience, some functions are invoked so often that tracing them leads to noise in the log. Many functions include the empty (exwm--log) call after a conditional for this reason. Maybe there is a way to disable some of them?

Another consideration is that we already have the exwm-debug minor mode. I wonder whether it would make sense to add this feature to it.