scribble/llncs fails to download llncs.cls

[fare]

The Springer ftp server doesn't exist anymore.
llncs is now at 2.23 not 2.20 anymore.

The page https://www.springer.com/gp/computer-science/lncs/conference-proceedings-guidelines has a link "LaTeX2e Proceedings Templates download " which points to https://resource-cms.springernature.com/springer-cms/rest/v1/content/19238648/data/v7 which resolves to a zip file that contains llncs 2.23.

There's also a copy on CTAN https://ctan.org/pkg/llncs that mentions a CC BY 4.0 license, and that might (or not) provide more stable URLs to download present and older versions from.

[fare]

Also, it is probably poor form to store an unversioned copy of the file in ~/.racket/llncs.cls — what if a version incompatibility were introduced at some point? scribble/llncs probably needs to ascertain that it's using a compatible version.

[samth]

The relevant CTAN link seems to be http://mirrors.ctan.org/macros/latex/contrib/llncs/llncs.cls

[fare]

If the license is compatible, I'd suggest including the cls file in the racket/scribble git repository, or a separate repository (if needed for license reasons) that can used as a submodule or stable place to download from.

[fare]

xref: https://racket.discourse.group/t/llncs-out-of-date/2558 (pointed me to here as the right place to report a bug).

[racket-discourse-github-bot]

This issue has been mentioned on Racket Discourse. There might be relevant details there:

https://racket.discourse.group/t/llncs-out-of-date/2558/4

[LiberalArtist]

It looks like the LaTeX class was originally released under a non-free license, but at some point (after 2013, but at least by 2022) was re-licensed by Springer to CC-BY-4.0. Racket can definitely distribute CC-BY-4.0 code, and using the CC-BY-4.0 will avoid a potential issue for downstream packagers with especially zealous license policies, too.

It seems like it could be reasonable to either:

1. Expect users to install llncs via their (2022 or later) TeX distribution; or
2. Distribute it with the scribble-lib package, as is already done for sigplanconf.cls and acmart.cls.

If adding llncs.cls, be sure to also add its license here!

scribble/scribble-lib/info.rkt

Lines 28 to 35 in f7f51eb

	(define license
	'((Apache-2.0 OR MIT)
	AND
	(CC-BY-3.0 ;; sigplanconf.cls
	AND
	(LPPL-1.3c+ ;; acmart.cls
	AND
	LPPL-1.0+)))) ;; pltstabular