Shadow's --data-template option copies a template directory to the data directory before running an experiment. By default, this is set to shadow.data.template. If someone's not familiar with this feature of Shadow, this default behaviour might not be very intuitive. Instead we should not set a default data template directory so that the user must set it explicitly.

For backwards-compatibility reasons, if the --data-template option was not set but a shadow.data.template directory exists, we should log a warning to let the user know that this default behaviour changed.

We discussed removing this option entirely and requiring the user to copy the template directory manually before running the experiment, and also to not automatically delete the shadow.data directory before running the experiment, since this could be considered outside of Shadow's responsibility. But there are some other problems to consider. For example, someone could run an experiment, and then immediately run it again, but since the files from the previous experiment would still exist, the results from the second experiment might be different which could be confusing to the user. It's not immediately obvious which approach is best.