Thanks for looking at it @tobiasdiez ...
unfortunately the jpackage tar returns a 404, it's no longer available on the oracle webpage!!
The rest of your fixes are great! I'm still learning how github actions work...

Yep, they updated to a later build and thus the paths changed. I tried to fix it with #5380 but that does not work at the moment. We have to wait a bit until some breaking changes to the jpackage interface are propagated trough the tool chain.

So the build is fixed upstream. Could you please rebase/merge the latest changes. Thanks

I had to merge because there were too many changes for a proper rebase, and it was not working properly..
At the end, if the snap build process works we can merge as a single commit to keep the git log a bit cleaner, now let's see it if works!

There are some problems with the snap build. Moreover, I was wondering if it is really necessary to wrap everything in the docker. apt get install snap raft (maybe after add-apt-repository ppa:snappy-dev/tools) is not possible?

Unfortunately it's not possible, being a core18 snap it needs to be built in a vm (multipass or lxc), and those do not work atm in a github actions vm.
One thing I can do is build a docker bionic image and use that. That should solve the issue

There are open issues related to having official support for either an official docker image or support directly in the github CI:
https://bugs.launchpad.net/snapcraft/+bug/1846195
canonical/multipass#1075

@tobiasdiez The snap build works now, so it can be uploaded to the jabref repo.
The next thing (that I obviously cannot do) is add the snapcraft secret file as described here: https://forum.snapcraft.io/t/building-and-pushing-snap-packages-from-gitlab/9537
The tldr is:
snapcraft login
snapcraft export-login snapcraft.login
base64 snapcraft.login | xsel --clipboard

paste to the SNAPCRAFT_LOGIN_FILE in secrets

Perfect! Thanks for your work.

@koppor @Siedlerchr can you please have a look at the upload stuff (and maybe add the login data to the admin repo?). Thanks

If you want we could first uncomment the upload to builds.jabred we could test the built snap from there before pushing to the snap store

It's not possible right now to use secrets in pull requests from forked repositories (https://github.community/t5/GitHub-Actions/Make-secrets-available-to-builds-of-forks/m-p/30678#M508). Thus, we cannot upload something to builds.jabref.org from a forked PR. Thus, I'll merge this now and hope everything runs.

Joining the party late. The snapcraft step is protected by a guard checking for the branch. This is an indicator that a separate "publish-on-snapcraft" workflow should be created. Running on ubuntu-latest and master branch only. Maybe just executing the single step is enough (after checkout).

@tobiasdiez Let's see if it works, then it can be moved out in a separate part, to expedite the upload of the other builds

It builds and uploads!
I can't download it to test it, but it looks like a good start ;)

Build was succesful! Congrats! @LyzardKing
Just a few things in the build log:

So the only missing part is the upload to the snapcraft?

The 'gnome-extension' part is missing libraries that are not included in the snap or base. They can be satisfied by adding the following entry for this part
stage-packages:
- libc6
Priming jabref 
The 'jabref' part is missing libraries that are not included in the snap or base. They can be satisfied by adding the following entries to the existing stage-packages for this part:
- libc6
- libgcc1
- libstdc++6
- libtinfo5
- libuuid1
- zlib1g
DEPRECATED: The 'version-script' keyword has been deprecated in favour of the 'snapcraftctl set-version' part scriptlet.

I agree it would be cleaner to extract the snap action to a separate workflow. However, it seems running workflows sequentially is not yet supported: https://github.community/t5/GitHub-Actions/Github-Actions-trigger-workflow-on-Succes-Failure-of-other/td-p/17944

@Siedlerchr The missing libraries error should actually be ignored because they are all in the gnome-extention snap.
The version-script can be fixed when the version is set in the jpackage tarball (I believe)

@LyzardKing Thanks for the update. Btw, I added you as collaborator, so you can directly create a new branch at the JabRef repo and can test it without needing to specify any secrets in your fork

Thanks!!
I'll create a branch when there's a new update to fix the snap then!
The one thing that needs work now is the snap store integration (the commented line under the snapcraft command in the github actions script)

@koppor The snap build reuses the jpackage build

Follow up discussions regarding the build at #5417.