RE: curiosity in value of "source-directory" in function "autoload-generated-file" and in the containing file "autoload.el.gz"

[Drew Adams <drew.adams@oracle.com>]

> I find it curious that the file
> "/Applications/Emacs.app/Contents/Resources/lisp/emacs-lisp/autoload.el.gz"
> has the following code:
> 
> (defun autoload-generated-file ()
>   (expand-file-name generated-autoload-file
>                     (if (not (local-variable-p 'generated-autoload-file))
>                         (expand-file-name "lisp" source-directory))))
> 
> and "source-directory" in this code has no other mention in this file,
> except in a comment.

`source-directory' is a predefined global variable.  `C-h v' tells
you this (where ... is filled in):

  source-directory is a variable defined in `C source code'.
  Its value is "..."

  Documentation:
  Directory in which Emacs sources were found when Emacs was built.
  You cannot count on them to still be there!