I got to the end of that without really understanding what this is solving, what it does, or how.
How do you handle changing upstream files locally without forking? Do you just, keep changes in a separate configuration format that is applied lazily at built time?
I've never had issues with maintaining a fork anyways.
The main advantage over plain "patch" is that it is more powerful in the face of upstream changes. For example if you rename the upstream file, you have no good way to represent this in .patch, but that project allows is. There also a way to specify patch using function name, which should make it more robust in face of upstream changes.
As for my opinion, this seems like an incremental improvement over existing tools. I'd prefer a simple shell script that does "git checkout ... && mv ... && cp .. && patch ..." over something fancy like this.
How do you handle changing upstream files locally without forking? Do you just, keep changes in a separate configuration format that is applied lazily at built time?
I've never had issues with maintaining a fork anyways.