Re-fill compilation-mode buffer from shell script

I have a similar script, and I just run it directly from M-x compile. In my case, the script runs continuously once started and triggers a recompilation on file change. Sounds like that should work for you? You'd run utman make debug unit test from compile, don't invoke emacsclient or anything.

Then, to get next-error working correctly on recompile, I do this.

1. Add a function to compilation-filter-hook to watch the script output for a special string the script emits on recompilation (for example purposes let's say that string is "Change detected, recompiling ...")
2. Call compilation-forget-errors when the string is found. (Note that the manual doesn't advertise this function, I found it by hunting around in the compile.el source code.)
3. Not technically necessary, but for quality of life I after-advise compilation-forget-errors to reset the mode-line counts of errors / warnings / info lines. For some reason it doesn't do that by default (in Emacs 27.1)

All in, my code snippet looks like this:

;;; this runs with the *compilation* buffer current.  see the documentation
;;; for `compilation-filter-hook'
(defun my/forget-compilation-errors ()
  (let ((inserted-string (buffer-substring-no-properties
                          compilation-filter-start (point))))
    (when (string-match-p "Change detected, recompiling" inserted-string)
      (compilation-forget-errors))))

(add-hook 'compilation-filter-hook #'my/forget-compilation-errors)

(defadvice compilation-forget-errors (after reset-num-errors-found activate)
  (progn
    (setq-local compilation-num-errors-found 0)
    (setq-local compilation-num-warnings-found 0)
    (setq-local compilation-num-infos-found 0)))

Actually that snippet up there is a bit of a lie. It's what I had at first. These days I actually always give a prefix argument to compile so that I get comint-mode + compilation-shell-minor-mode. That way I can interact with my script if it prompts for input, which it does sometimes, and I can cleanly shut it down with C-c C-c. The same principles apply, it's just I have to use a different hook. So my actual code snippet now looks like:

(defun my/forget-compilation-errors (inserted-string)
  (prog1 inserted-string
    (when (string-match-p "Change detected, recompiling" inserted-string)
      (compilation-forget-errors))))

(add-hook 'comint-preoutput-filter-functions #'my/forget-compilation-errors)

(defadvice compilation-forget-errors (after reset-num-errors-found activate)
  (progn
    (setq-local compilation-num-errors-found 0)
    (setq-local compilation-num-warnings-found 0)
    (setq-local compilation-num-infos-found 0)))