Checking and fixing broken links on GAP website

[olexandr-konovalov]

This is a snippet of the command to check html links on GAP website with linklint:

linklint -limit 100000 -doc gaphtml -http -host www.gap-system.org -skip /ForumArchive/@ /@

We should run it periodically. In fact, I already have a Jenkins job that does that, but because it reports a number of issues, it is not practical to fail it automatically yet.

[olexandr-konovalov]

We should certainly try to fix them if the solution is in this repository (IIRC last big cleanup of broken links was a while ago), and report to package authors otherwise. One of the common problems in packages is misssing .css and .js files that are produced by GAPDoc but not included in the archive.

[fingolfin]

Perhaps we can setup a travis job to run this link checker?

[fingolfin]

Another interesting link checker: https://github.com/gjtorikian/html-proofer

It also can check external links, but one can also configure it to turn that off. With external link checks, it takes quite some time to run, but no problem for a daily cron job.

I'd love to run these things in Travis, but one thing that makes this problematic is that for example links to package manuals would be broken there. But perhaps we can find a way around that, e.g. by installing the missing manuals in the Travis job?

[fingolfin]

@schnellecom run a link check for the website relaunch in PR #339 and fixed many broken links.

Perhaps we could use a GitHub action like https://github.com/marketplace/actions/check-links-with-linkcheck or https://github.com/marketplace/actions/link-check-action to check for broken links more systematically?