pkg_tar can detect when there are file conflicts (code). However, when it detects them, it prints them instead of failing. I see no reason why anyone would want it on print other than for backwards compatibility (which I assume is why it was first added), but if anyone can think of a reason, please tell me.

I'm happy to implement this myself. However, there are a few ways we could do it, and I don't know what the best approach would be to take. I was looking for approval / feedback on the best approach to take.

Option 1: Simple cutoff
Change print to fail, and maybe increment the major version to indicate backwards incompatible changes. Alternatively, we may consider waiting for a major version increase to do this.

Option 2: Feature flag
Create a bool_flag that controls whether it prints or fails. Initially default it to false, and when we release other backwards incompatible changes, we can set it to true.