go-git is a highly extensible git implementation library written in pure
Go.  It can be used to manipulate git repositories at low level
(plumbing) or high level (porcelain), through an idiomatic Go API. It
also supports several types of storage, such as in-memory filesystems,
or custom implementations, thanks to the Storer interface.

It's being actively developed since 2015 and is being used extensively
by Keybase, Gitea or Pulumi, and by many other libraries and tools.