Fix an issue when both export-dir and tarball-dir is set

[mochrul]

When the export-dir is set, the git tree is archived and then re-extracted
into the new place. Unfortunately, different directory is in use to create
the archive (output_dir) and then to extract it (tarball_dir, controlled by
the tarball-dir option). This means that if no orig.tar.gz is provided in
the tarball_dir directory, the extraction will fail.

[agx]

can you demonstrate this with a testcase tests/component/deb that fails initially and works after your fix?

[mochrul]

WIP

[agx]

I'm a bit puzzled since if you use overlay then isn't the whole point that we're not generating an archive but use tarball-dir?

[mochrul]

Yes, you are completely right. To be honest, I inherited/stole the gbp configuration, and as it worked correctly for years, I haven't checked the actual meaning of the options. (It worked because the first step was to download the new upstream version and that step did generate the orig.tar.gz, so the issue is not triggered. This was the first time I started to work on the project in a different computer where I downloaded the upstream version).

To be honest, I tried to create the test case and reproduce the issue for a very long time before I realized that the overlay option also has its role in the game. And thinking the more about it the less I'm confident about the solution. But I'm still confident that this should be handled somehow, maybe with a correct error message.