Re: jar files won't open in emacs 27.1 on debian 11.6 "bullseye"

[Steinar Bang]

>>>>> Eli Zaretskii <eliz@gnu.org>:

> I cannot reproduce this with a random .jar file I have here and with
> Emacs 27.1.  So I guess this is something specific to that particular
> jar file.

Indeed. I walked down into ~/.m2/repository/ and tried the first jar
there, which happened to be antlr-2.7.7.jar and that opened fine.

I've been doing this with jar files for years (decades, even,
maybe...?), on multiple platforms (various GNU/linux distros and
versions, mac OSX, various windows versions) and over many emacs
versions.

And I've never seen this behaviour before.

Hm... seems to be a problem on everything I've build myself...?
At least: everything I've recently built myself on this computer.

FWIW I'm using java11 and maven-jar-plugin 3.2.0 (if that rings a bell
for someone out there somewhere...?)

>> Any idea of how to debug this?

> Step with Edebug through arc-mode.el and see why it signals the error?
> It is possible that the jar file you tried uses some extensions of the
> ZIP format which were not yet supported in Emacs 27, so perhaps try
> with a later version of Emacs.

no luck with edebug so far.

I first did (setq debug-on-error t) in a fresh emacs and got the
following stack trace from attempting to open the javadoc file:
 https://gist.github.com/steinarb/234cf172c214b26b33ee92a4e5b5afd1
and found archive-zip-summarize which looks promising (and is in
arc-mode.el) 

Then I opened a new fresh emacs and openet 
/usr/share/emacs/27.1/lisp/arc-mode.el.gz
and but the cursor over archive-zip-summarize and did 'C-u C-M-x'

Then I tried opening the javadoc.jar but, unfortunately it didn't stop
in archive-zip-summarize

Not sure what more to do to make the code stop in the debugger (I have
skimmed the edebug docs to get this far).

>> Does the zip support of emacs 27.1 come in the form of running unzip in
>> a sub-process? Or does it use a linked in library? (libbz2...?)

> Neither.  Just visiting a zip file doesn't require any of that, at
> least not by default (I have no idea whether Ubuntu made any changes
> in the upstream sources or in site-wide customizations).

Thanks for the info.

FWIW From what you describe above, I doubt there are any modifications
in ubuntu/debian on the lines I was asking about (but I haven't actually
checked).

Thanks!


- Steinar