[ruuda]

If the upstream project does not want to merge your fix, but it's an obvious improvement and a non-controversial patch, then one option is to have packagers carry the patch instead. For example in Nixpkgs, it is quite easy to patch an upstream project. If you then want to step in and keep the patch rebased, that's great. If you throw it over the fence and later the patch starts to conflict, then the packagers would likely remove it. It shouldn't be the first thing you try, but it can be a valid alternative with unworkable upstreams.

[orangepurple]

You don't need a fancy Nixpkgs setup. GNU Patch works just fine and its 37 years old.

[ruuda]

It works fine for applying the patch, but then you have to manually follow all of the build steps, turn it into a distribution package, etc. With Nix it is easy to edit an upstream package that already knows how to build the software, to include the patch.

[orangepurple]

I have been doing this with the Arch Linux AUR for many years and it works well too