Confused about `phpstan-working-dir`

[MarkRedeman]

Hi, thanks for this great package!

I'm a bit confused about the usage of the phpstan-working-dir variable.

I'm trying to setup phpstan.el so that I don't have to have a phpstan.neon file in a project.
I got this working by setting (setq phpstan-working-dir ".") so that the enabled check passes, however this seems very hacky.

Could you explain to me the use of phpstan-working-dir? The documentation mentions it should be different than the project root but doesn't give an explicit example.

---

In addition, I think I've found a bug while trying to figure out the use case of phpstan-working-dir. I tried the same "hack" (not having a phpstan.neon file and setting (setq phpstan-working-dir ".")) when using Docker.
In this case phpstan-get-config-file returns NIL which is passed to phpstan-normalize-path however since prefix is set to /app the function throws an error

Debugger entered--Lisp error: (wrong-type-argument arrayp nil)
  replace-regexp-in-string("\\`/home/mark/Projects/testing-phpstan/" "" nil t t)

This is easily fixed by changing the function:

(defun phpstan-normalize-path (source-original &optional source)
  "Return normalized source file path to pass by `SOURCE-ORIGINAL' OR `SOURCE'.

If neither `phpstan-replace-path-prefix' nor executable docker is set,
it returns the value of `SOURCE' as it is."
  (let ((root-directory (expand-file-name (php-project-get-root-dir)))
        (prefix
         (or phpstan-replace-path-prefix
             (cond
              ((eq 'docker phpstan-executable) "/app")
              ((and (consp phpstan-executable)
                    (string= "docker" (car phpstan-executable))) "/app")))))
-    (if prefix
+    (if (and prefix source-original)
        (expand-file-name
         (replace-regexp-in-string (concat "\\`" (regexp-quote root-directory))
                                   ""
                                   source-original t t)
         prefix)
      (or source source-original))))

I'm happy to send a PR to fix the above issue however, it seems quite hacky.