git is licensed GPL-2.0-only; this library is MIT (see LICENSE). It is written from git's observable behaviour, never from its code:

• Never read git's source: its C files and headers, scripts, test suite (t/), patches, diffs or blame, wherever they are (GitHub, kernel.org, mailing lists, a local checkout, a search engine snippet). The same goes for any GPL-licensed implementation, libgit2 included.
• Allowed: running the git binary, which is the oracle; git's user documentation (man pages, git-scm.com), its release notes, and its commit messages (not their diffs), to establish whether a behaviour is a bug. Learn from them; do not copy their text.
• Behaviour is established by experiment and recorded as test vectors in GIT-BEHAVIOUR.md, with the git version used.
• Code, comments, documentation and commit messages never name git's internal functions, variables or source files.
• If a task seems to need git's source, stop and ask.