Allow simpler config for license checks

[luser]

AFAICT currently the licenses check requires explicitly listing out allowed licenses since step 5 states that crates that don't match any other rules are implicitly rejected.

For our usage I would ideally like to be able to specify a list of denied licenses without having to spell out all of the allowed licenses. My initial thought was to simply use something like:

[licenses]
unlicensed = "deny"
copyleft = "deny"

This causes the license check to fail since I don't have an allow list. Perhaps being able to change the default behavior for step 5 would be the simplest fix? Something like:

[licenses]
unlicensed = "deny"
copyleft = "deny"
default = "allow"

If this is not something you'd consider, perhaps a "generate a valid configuration that allows all of the licenses for crates currently in use" command would be helpful.

[Jake-Shadle]

So just to be clear, the allow-osi-fsf-free field doesn't handle your use case? I will add a default field because it is useful to allow changing that default rejection behaviour, but just curious if you have an example of a license that you would still want to allow that doesn't match a license that is in the OSI or FSF categories.

[luser]

That is a good question and I suspect it might but I found that option confusing to think about so I'm not sure!

[Jake-Shadle]

Oh? Do you have any idea on how the option could be simpler and easier to understand?