Get latest commit hash from remote URL

[jakewilliami]

Is it possible to get the latest commit hash from a remote URL with gitoxide? I was thinking of using perhaps gix-traverse or gix-commitgraph, but I can't find any code that allows me to construct the commit graph from a remote URL. I can also see that gix::Repository::head_id might be useful, but I don't know how I call this with a gix::Remote.

For example, here's how this would be done using git2:

let url = format!("https://github.com/{}/{}.git", GITHUB_USER, GITHUB_REPO_NAME);
let mut repo = git2::Remote::create_detached(url).expect("Cannot create remote repo instance");
repo.connect(git2::Direction::Fetch).expect("Cannot connect to remote repo");

let remote_heads = repo.list().expect("Cannot get remote head list from remote repo");
let commit_map: HashMap<String, String> = remote_heads
    .iter()
    .map(|rh| (rh.name().to_string(), rh.oid().to_string()))
    .collect();

repo.disconnect().expect("Cannot disconnect to remote repo");

// get /refs/heads/{branch} or HEAD from commit_map

So this can easily be done using gitoxide's git2 interface, however I'm wondering if there is an easier way to do it?

[Byron]

It is, and what you are looking for seems to be what's implemented in gix remote -n https://github.com/git/git refs. The code can be found here. I hope that helps.

[jakewilliami]

That is somewhat helpful. However, how is the remote repository constructed? It looks like it's just passed as a function parameter.

Also note that I only care about the latest commit, not all of them, in case that changes the compute time.

[Byron]

However, how is the remote repository constructed? It looks like it's just passed as a function parameter.

Repository instances can be opened or discovered.

Also note that I only care about the latest commit, not all of them, in case that changes the compute time.

One can restrict the selection of references to observe the last known state from by controlling a remote's refspecs.

[jakewilliami]

Repository instances can be opened or discovered.

Sorry to be a pain, but I'm still having trouble with this. To be clear, I don't have the repository locally. However, I know the URL. It looks like both open and discover expect a local path to the repository. Is it possible to construct a repository given only its remote URL, such as git2's Remote::create_detached?

[Byron]

The real answer is that even though one can query remote references, one can't do so without a 'real' Repository instance.

---

Thanks so much for pointing this out! Clearly that's a hole in the API as currently there is no way to get a Remote without a Repository, nor is it possible to get an in-memory repository. Right now the only workaround would be to have a physical repo on disk, but that's probably not really a workaround anyway.

It seems that the only reasonable thing to do with a Remote without Repository is to list remote references, and that could be put into its own utility function. After all, gitoxide's plumbing crates are made to operate with only the bare minimum of information that's needed to perform a particular job. There is a lot wrong with having entirely standalone interactions with remotes as surprising amounts of configuration may contribute to successful connections in the first place, but that's certainly to be solved when fleshing out such API. Thinking about it again, it's probably easier to allow opening an 'anonymous' repository that loads all the usual configuration, but has no effective access to any .git repository, so Repository::remote_at(<url>) can be used naturally if some care is taken to specifically support this usecase. Maybe in the end, the API for that would end up being similar to the one in git2 :).

[jakewilliami]

Thanks heaps Sebastian, good to know! Happy to help discover holes in the API, and looking forward to what this might become in the future. Gitoxide is amazing, and I love the ecosystem of minimal crates for specific tasks. Great work, and thanks again :)