byte compile file-local variables

Question

Is it possible to access a user-defined file-local variable during byte-compilation?

As an example, I am trying to get this code to work:

--- testfilelocals.el ---
;; -*- my-file-local: "foo" -*-

(defun testfilelocals ()
  (eval-when-compile 
    my-file-local))

which fails with a compiler error

testfilelocals.el:5:5:Error: Symbol's value as variable is void: my-file-local

Answer 1

Looking at the source code in bytecomp.el, one can see that only safe file-local variables are read (see the relevant part of the file below).

This means that if you declare your variable as safe for file-local use, it should be read when you compile your file. You can for example evaluate the following piece of code before you byte-compile the file:

(put 'my-file-local 'safe-local-variable 'stringp)

---

For reference, here is the relevant part of bytecomp.el:

(let ((buffer-file-name filename)
      (dmm (default-value 'major-mode))
      ;; Ignore unsafe local variables.
      ;; We only care about a few of them for our purposes.
      (enable-local-variables :safe)
      (enable-local-eval nil))

Answer 2

Maybe because you did not specify major mode where the variables are used:

;; -*- mode: Lisp; my-file-local: "foo" -*-

Most major modes reset all variables upon initialization.