Earlier quoted context omitted.
This raises some interesting legal questions. If I start a git repo and only add a license in the Nth commit, does that license apply retroactively to a checkout of the first N-1 commits? What if I start out with one license but I change it in the Nth commit? If someone clones the git repo with the Nth commit in it and then checks out an earlier commit, which license applies? (For simplicity, assume I am the only aut…
You can retroactively make a license more open, but you cannot retroactively make it more closed.
Let's suppose Alice gives Bob a copy of code whose copyright is owned by Charles, and the code was licensed to Alice under and open/free license.
If the license is revocable, Charles should be able to revoke the licenses for existing copies, and offer replacements that are more closed. Those who do not accept that replacement license should, I think, be able to continue using the copies they have but they will not have a license. Their rights will be limited to those rights that copyright law gives to owners of legally made copies. For software, that would mean they could use the code, but could not make and distribute copies or derivative works.
If the license is irrevocable, then Charles should not be able to take away existing licenses, but he may be able to stop issuing new licenses. That brings is to the issue of sub-licensing. If the license is sub-licensable, then when Alice gives Bob a copy, Alice can also give Bob a license via her sub-licensing right.
If the license is not sub-licensable, then Alice cannot give Bob a license. Bob's license has to come from Charles. So what happens if before Alice gives Bob a copy, Charles has decided to stop issuing new licenses?
I think Alice should still be able to distribute to Bob, because she has a license that allows distribution. Without a license from Charles, though, Bob would only be able to use the code for things copyright allows the owner of a particular legal copy to do without a license, which would be use it himself but would not include making and distributing copies and derivative works.
Alice might be able to argue that the terms of her license with Charles require Charles to provide licenses to those whom Alice distributes to, and so perhaps Alice could go to court to force Charles to keep granting licenses.
I don't recall enough from law school about third party beneficiaries to figure out whether Bob could sue Charles based on Alice's license to get a license from Bob for a copy he got from Alice, or whether, if Charles sued Bob for copyright infringement Bob could use Charles' contractual obligation to Alice in his defense.