If the project is using `git` and tags each release, it is really easy to ask `git` which tag is the first to contain a given commit.

For instance, take 58a46bf on Sunspot which added the `Sunspot.optimize` method:

$ cd /path/to/sunspot
$ git describe --contains 58a46bf
v1.2.0~22

In this case, `v1.2.0` was the first tag to contain the commit in its tree, and it was `22` commits away.

To use `Sunspot.optimize`, you’d need at least Sunspot v1.2.0.