libgit2 - 查找指向提交的标签的最快方法是什么？

Question

使用 libgit2sharp 我想执行以下操作:

foreach( Commit commit in repo.Commits )
{
    // How to implement assignedTags?
    foreach( Tag tag in commit.assignedTags ) {}
}

我想获取分配给当前提交的所有标签。最好的方法是什么？遍历所有标签并查看是否 tag.Target.Sha == commit.Sha？那不是很高效。还有别的办法吗？

Answer 1

So I want to get all tags assigned to the current commit. Whats the best way to do that? Iterate through all Tags and see if tag.Target.Sha == commit.Sha? Thats not very performant. Is there another way?

涉及标签时需要考虑两件事。

• 标签可以指向提交以外的其他内容(例如，树或 Blob)
• 一个标签可以指向另一个标签(链式注释标签)

考虑到上述几点，下面的代码应该可以满足您的需求。

注意: repo.Commits 只会枚举可从当前分支 (HEAD) 访问的提交。下面的代码扩展它可以轻松浏览所有可到达的提交。

...

using (var repo = new Repository("Path/to/your/repo"))
{
    // Build up a cached dictionary of all the tags that point to a commit
    var dic = TagsPerPeeledCommitId(repo);

    // Let's enumerate all the reachable commits (similarly to `git log --all`)
    foreach (Commit commit in repo.Commits.QueryBy(new CommitFilter {Since = repo.Refs}))
    {
        foreach (var tags in AssignedTags(commit, dic))
        {
            Console.WriteLine("Tag {0} points at {1}", tags.Name, commit.Id);
        }
    }
}

....

private static IEnumerable<Tag> AssignedTags(Commit commit, Dictionary<ObjectId, List<Tag>> tags)
{
    if (!tags.ContainsKey(commit.Id))
    {
        return Enumerable.Empty<Tag>();
    }

    return tags[commit.Id];
}

private static Dictionary<ObjectId, List<Tag>> TagsPerPeeledCommitId(Repository repo)
{
    var tagsPerPeeledCommitId = new Dictionary<ObjectId, List<Tag>>();

    foreach (Tag tag in repo.Tags)
    {
        GitObject peeledTarget = tag.PeeledTarget;

        if (!(peeledTarget is Commit))
        {
            // We're not interested by Tags pointing at Blobs or Trees
            continue;
        }

        ObjectId commitId = peeledTarget.Id;

        if (!tagsPerPeeledCommitId.ContainsKey(commitId))
        {
            // A Commit may be pointed at by more than one Tag
            tagsPerPeeledCommitId.Add(commitId, new List<Tag>());
        }

        tagsPerPeeledCommitId[commitId].Add(tag);
    }

    return tagsPerPeeledCommitId;
}