Re: End of file while generating loaddefs.el

[Eli Zaretskii <eliz@gnu.org>]

> Date: Sat, 21 Nov 2015 12:23:52 +0100
> From: martin rudalics <rudalics@gmx.at>
> CC: emacs-devel@gnu.org
> 
> Do you still have the snippet that caused problems in your case?

Yes, I do.

> How could null bytes possibly get into that file

I don't know.  Some bug, obviously, but that's all I can say.  I also
know it happened 7 days ago, because that's the time stamp of the
file.

> and why did they cause an end of file exception during parsing?

That's easy.  This is the guts of autoload-read-section-header:

      (while (looking-at generate-autoload-section-continuation)
	(forward-line 1))
      (setq string (buffer-substring beginning (point)))
      (with-current-buffer (get-buffer-create " *autoload*")
	(erase-buffer)
	(insert string)
	(goto-char (point-min))
	(while (search-forward generate-autoload-section-continuation nil t)
	  (replace-match " "))
	(goto-char (point-min))
	(read (current-buffer))))))

The null bytes cause the first while loop to stop prematurely, and
then buffer-substring copies only part of a sexp into a temporary
buffer.  We then try to read an incomplete sexp from that buffer and
hit the end of the buffer before the sexp ends.

> And why does no one else have such problems?

I don't know, because I don't know what bug caused those null bytes to
appear in the first place.