I managed to get this working by following the referenced discussion. To save other people time, here's the code I ended up using.

const git = require('nodegit')

;(async () => {
  const repo = await git.Repository.open('.')
  const refs = await repo.getReferences(git.Reference.TYPE.OID)
  const tagRefs = refs.filter((ref) => ref.isTag())
  const tagRef = tagRefs[0]
  const targetRef = await tagRef.peel(git.Object.TYPE.COMMIT)
  const commit = await repo.getCommit(targetRef)
})()

The important line is this one:

const targetRef = await tagRef.peel(git.Object.TYPE.COMMIT)

Unlike with a branch reference, you have to peel a tag reference back to the commit to which it points.

I found this is necessary regardless of whether the tag is annotated or lightweight.

This really feels like a dirty part of the API. Can we agree on an API that allows a program to navigate from a tag to a commit in a more elegant way?

@mojavelinux The following code should work.

const repository = await git.Repository.open('.')
const reference = await repository.getReference("refs/tags/tagName");
const commit = await reference.peel(NodeGit.Object.TYPE.COMMIT):

It's not completely clear to me what you are looking for though. You want a way to go from the name of a tag to its commit or from an actual Tag object to its commit?

@rcjsuen That's precisely what the code I showed is doing. We're just getting the references a different way. (My code is discovering the references since I don't know the names up front).

It's not completely clear to me what you are looking for though.

My use case is simple. I want to read the files in a tag by walking the tree. For that, I need to resolve the tree. The tree is accessible from a commit. So the first thing I need to do is find the commit.

I'm using this in a content system that reads files from the branches and/or tags of a bare git repository.

@mojavelinux Never mind, I think I misunderstood what you originally were trying to say. Sorry about that.

There is a related discussion about these APIs at #403.

Thanks for the pointer!