@layus, thanks for your PR! By analyzing the history of the files in this pull request, we identified @elitak, @Baughn and @mpscholten to be potential reviewers.

For me, the demo tarball downloaded is gzip compressed, so renaming it to .xz causes the unpack phase to fail. You'll need to provide a modified name attr to the fetch instead of inheriting the common one.

Also maybe fix the inconsistent spacing around the fetchurl/authenticatedFetch/abort (right-justify the verbs) and maybe rename versions to releases.

@elitak How can it fail for you and not for me ? This is scarier than the issue itself.

@layus Run file /nix/store/*factorio-demo*tar.[gx]z and see if the contents match the extensions. I can't really offer an explanation for this behavior on the master branch unless you rebased from an older one, since I think the tar xaf behavior in stdenv changed to xz -d | tar x at some point in recent history. Regardless, the extensions should match the contents of any files written to the store, especially when used as src attributes.

@elitak It wan indeed the rebase. Factorio uses xz for 0.15.x apparently, and the demo is still stuck at 0.14.x. Also fixed the other nitpicks.