How to specify the directory for file-exists/delete-file/byte-compile-file?

Question

I thought it would be great to save a Elisp file (in my init), and it compiles automatically a byte-compile Elisp-file.

So I wrote a function for this.

    (defun remove-elc-and-compile-on-save ()
      "If you're saving an elisp file, likely the .elc is no longer valid. And automatically byte-recompile this file whenever it's saved."
      (interactive)
      (if (file-exists-p (concat buffer-file-name "c"))
          (delete-file (concat buffer-file-name "c"))
        nil)
      (byte-compile-file buffer-file-name)
      )

    (add-hook 'emacs-lisp-mode-hook 
              (lambda () 
                (add-hook 'after-save-hook 'remove-elc-and-compile-on-save nil 'make-it-local)))  

For example, the directory structure where my Elisp files are: C:\foobar\Emacs\setup-foobar.el. (It's a Windows structure).

It works perfectly. However, my Emacs directory with the Elips-files will be spoiled with the compiled .elc-files all over the place. So I thought to move the .elc-files to a specific directory.

For example, the directory structure where my Elisp files are: C:\foobar\Emacs\setup-foobar.el. (It's a Windows structure).

Then I would like to move the .elc files to C:\foobar\Emacs\setup\setup-foobar.el. When I checked the documentation of the functions file-exists-p, delete-file, byte-compile-file, there is no optional parameter available to specify the path where the delete/compilation operations should occur. They're executed in the same directory as the buffer-file-name.

I tried another ways like:

(byte-compile-file (concat "C:/foobar/Emacs/setup/" buffer-file-name))

But it didn't worked out, and it's not applicable for the file-exists-p and delete-file functions.

So I'm wondering in which way I could specify the path where the operations should be executed, instead in the same directory as the buffer?

Answer 1

1. I agree with @wvxvw's comment: You don't need to move the *.elc files; it is enough to not look at them. ;-) You can hide them from a Dired listing, for example.

2. But if you really want to have byte-compiling automatically put the *.elc result in a different directory then you can set variable byte-compile-dest-file-function to a function that is similar to byte-compile-dest-file but which uses a different directory. Something like this:

(setq byte-compile-dest-file-function #'my-byte-compile-dest-file)

(defvar my-bytecomp-dir "/PATH/TO/YOUR/ELC/DIRECTORY/")

(defun my-byte-compile-dest-file (filename)
  "Like `byte-compile-dest-file', but put `*.elc' in directory `my-bytecomp-dir'."
  (setq filename  (file-name-sans-versions  (byte-compiler-base-file-name filename)))
  (expand-file-name
   (file-name-nondirectory
    (cond ((string-match emacs-lisp-file-regexp filename)
           (concat (substring filename 0 (match-beginning 0)) ".elc"))
          (t (concat filename ".elc"))))
   my-bytecomp-dir))