a) you should not be the owner (to avoid pet projects that are not actually useful) of the project or at least not the sole owner
b) ideally it should be some high impact projects that have little to no corpo sponsors as opposed to something like React
c) if your contribution is not merged in, it should not count as "work done"
I think it would be difficult to come up with a good metric. For example, it should not be based on some easily faked number governed by a foreign company.