Ask HN: Best way to quantify developer productivity for upwards reporting

I realize the the ask is a bit ambiguous, and even a bit controversial. Just to get this out of the way: I do agree that there is no perfect method of quantifying a developer's contributions, but I also believe that something useful can come out of such metrics. They absolutely should be only one of many vectors when determining a developer's effectiveness and value.

That said, I've used GitPrime previously (I think they were purchased w/ a recent name change). Was never a big fan of GitPrime, and was concerned with some of the hand-wavy answers I received when attempting to surface how specific metrics were calculated. In fact, some of the metrics were quite misleading, and the method in which some of these were calculated was not easily adjustable to fit the team's workflow, or so I was told.

So, if GitPrime isn't appropriate, what tool is? Or is there such a tool? How do you quantify a developer's performance & value based on available data (such as git activity, etc). Or is this just a fool's errand and the best course is to be a good manager who stays on top of the daily work your team is involved in? If so - how do you summarize your findings such that they have meaning across multiple teams?