GNU bug report logs - #39233
.elc file - possibly outdated backward compatibility comments

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From: Stefan Kangas <stefan <at> marxist.se>
To: Lars Ingebrigtsen <larsi <at> gnus.org>
Cc: Eli Zaretskii <eliz <at> gnu.org>, 39233 <at> debbugs.gnu.org, Stefan Monnier <monnier <at> iro.umontreal.ca>
Subject: bug#39233: .elc file - possibly outdated backward compatibility comments
Date: Fri, 24 Jan 2020 17:08:20 +0100

Lars Ingebrigtsen <larsi <at> gnus.org> writes:

> Reading the fix for the compilation problem, it was:
>
> -    (search-forward "\n;;; This file uses")
>
> It's quite possible that I misunderstand the patch, but doesn't this
> mean that (until a couple of days ago), Emacs assumed that that string
> exists in .elc files unconditionally.  And now it does, so if you try to
> use an Emacs from last week to load .elc files from this week, that
> week-old Emacs will break?

That code is only run during byte-compilation, not when loading the
file.  We add the lines, and then use them as an anchor to find the
location to add a version test for Emacs <23 if there are any utf-8
non-ASCII characters.

You could try on Emacs 26.1 `M-x load-file RET cperl-mode.elc RET'
using a file byte-compiled with current master to verify.

Best regards,
Stefan Kangas

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