core.el

;; works, but only for already opened buffers
(defun projectile-cleanup-project-buffers ()
  (interactive)
  (dolist (buffer (projectile-project-buffer-names))
    (condition-case nil
        (with-current-buffer buffer
          (esk-cleanup-buffer))
      (buffer-read-only nil))))

;; doesn't work - intended to get it to run against all 
;; project buffers even ones that aren't opened yet
(defun projectile-cleanup-project-files ()
  (interactive)
  (dolist (filename (projectile-current-project-files))
    (condition-case nil
        (with-current-buffer (find-file filename)
          (esk-cleanup-buffer))
      (buffer-read-only nil))))

find-file does not return a buffer object/name. It opens the file and a buffer and selects it. You can iterate through the files, run esk-cleanup-buffer, save the buffer and kill it. I guess it might be useful if I added to projectile some command that abstracts the iteration, saving and killing away.

@bbatsov yeah I was thinking it'd be nice to have 2 functions:

1. that calls a supplied fn for every buffer in the project
2. that calls a supplied fn for every file in the project

@bbatsov so pumped to have learned enough elisp to have got this to work, thanks to your tip :)

(defun cleanup-file (filename)
  (interactive "sFile: ")
  (find-file filename)
  (let ((name (buffer-name))
        (filename (buffer-file-name)))
    (if (not (and filename (file-exists-p filename)))
        (error "Buffer '%s' is not visiting a file!" name)
      (progn
        (esk-cleanup-buffer)
        (save-buffer)))))

(defun projectile-current-project-file-full-paths ()
  (let ((root (projectile-project-root)))
    (mapcar (lambda (filename)
              (expand-file-name filename root))
            (projectile-current-project-files))))

(defun projectile-cleanup-project-files ()
  (interactive)
  (dolist (filename (projectile-current-project-file-full-paths))
    (cleanup-file filename)))

Yep, I think you're right. Open a ticket about the two functions in Projectile's issue tracker and I'll attend to them at some point.

Glad to hear my previous comments where helpful. Btw, without kill-buffer in cleanup-file you'll end up with a ton of open buffers in any bigger project.