Make it easier to supply custom archive to `packit srpm`

I see. Makes sense. But it would be good to have a little bit more easier / straightforward way how to prepare the upstream archive. For fmf I had to add three Makefile targets plus this:

   current_version_command: ["make", "packit-version"]

   actions:
       create-archive:
       - make packit-tarball
       - make packit-path

I believe it should be much simpler/shorter/obvious.

_Originally posted by @psss in https://github.com/packit-service/packit-service/issues/103#issuecomment-541553803_

[psss]

Nice, thanks! Trying with https://github.com/psss/tmt/pull/249. Does not work…

[lachmanfrantisek]

@psss Your example looks good to me.

Or is it possible now to have only a single create-archive command?

Yes, if it contains archive-name in the output.

If there are more steps, then one of them has to return the archive name.

We run the commands one-by-one and then go through the output in reverse order and for each line of the output (also in the reverse order), we check if it is an existing file. If yes, we accept that as a newly created archive. I know, it’s a bit complicated but should work for most situations.