Git clone shallow depth=1 --branch=TAG: `error: reference not found` for given Tag as branch

[marcellodesales]

The git shallow is something we are looking at to solve clones of a single revision requested by Tag. The way to implement it is to use the shallow clones of a particular revision (branch, tag or SHA). The first test with git shows the single revision, cloned to dir /tmp/protobuf2, gives the expected result, while the one with go-git is failing with error: reference not found...

Regular Git Shallow

• Get a single Tag version
  • Meaning, a depth=1
  • https://stackoverflow.com/questions/14872486/retrieve-specific-commit-from-a-remote-git-repository/30701724#30701724
  • Cloned to a directory called /tmp/protobuf2

$ git clone --depth=1 https://github.com/protocolbuffers/protobuf --branch v3.10.0  /tmp/protobuf2
Cloning into '/tmp/protobuf2'...
remote: Enumerating objects: 2415, done.
remote: Counting objects: 100% (2415/2415), done.
remote: Compressing objects: 100% (1769/1769), done.
remote: Total 2415 (delta 941), reused 1200 (delta 524), pack-reused 0
Receiving objects: 100% (2415/2415), 5.08 MiB | 1.20 MiB/s, done.
Resolving deltas: 100% (941/941), done.
Note: switching to '6d4e7fd7966c989e38024a8ea693db83758944f1'.

You are in 'detached HEAD' state. You can look around, make experimental
changes and commit them, and you can discard any commits you make in this
state without impacting any branches by switching back to a branch.

If you want to create a new branch to retain commits you create, you may
do so (now or later) by using -c with the switch command. Example:

  git switch -c <new-branch-name>

Or undo this operation with:

  git switch -

Turn off this advice by setting config variable advice.detachedHead to false

• Result is a history with the single commit

$ git --no-pager lol
* 6d4e7fd (grafted, HEAD, tag: v3.10.0) Merge pull request #6721 from protocolbuffers/rafi-kamal-patch-1

go-git returns error: reference not found when refs/tag or ref/heads is not provided

• Get single tag version request
  • Modified the version of the clone at https://github.com/src-d/go-git/blob/master/_examples/clone/main.go#L18 *User needs to know the type of the reference a priori
  • without ref/tags/ for Tag or ref/heads for Branch the library fails with error: reference not found

func main() {
        // Clone the given repository to the given directory
    CheckArgs("<url>", "<directory>")
    url := os.Args[1]
    directory := os.Args[2]
    revision := os.Args[3]

    // Clone the given repository to the given directory
    Info("git clone --depth=1 %s --branch %s %s", url, revision, directory)

    r, err := git.PlainClone(directory, false, &git.CloneOptions{
        URL:               url,
        Depth: 1,
        ReferenceName: plumbing.ReferenceName(revision),
    })```

* Execution failed with the following

```console
$ go run go-git-cloner.go https://github.com/protocolbuffers/protobuf $(pwd)/protobuf v3.10.0
git clone --depth=1 https://github.com/protocolbuffers/protobuf --branch v3.10.0 /tmp/protobuf
error: reference not found
exit status 1

How to get ReferenceName for either a Branch, Tag, or SHA?

• Is there a way to fetch the proper referenceName by a given value?
  • Looking at https://github.com/src-d/go-git/blob/master/plumbing/reference.go, can't find anything that fetches before doing a clone, if that's the case...
  • Should clone resolve that with a single instance of Reference?

[marcellodesales]

Could get this for tag or branch, but I found out there are some limitations for SHA...

solution

• I got the solution after looking at the code...

func main() {
    CheckArgs("<url>", "<directory>", "<revision>", "type")
    url := os.Args[1]
    directory := os.Args[2]
    revision := os.Args[3]
    cloneType := os.Args[4]

    var repo *git.Repository
    var err error

    if cloneType == "branch" {
        Info("git clone --depth=1 %s --branch %s %s", url, revision, directory)
        repo, err = git.PlainClone(directory, false, &git.CloneOptions{
            URL:               url,
            Depth: 1,
            // Branch       ReferenceName: plumbing.ReferenceName("refs/heads/" + revision),
            ReferenceName: plumbing.NewBranchReferenceName(revision),
        })

    } else if cloneType == "tag" {
        Info("git clone --depth=1 %s --tag %s %s", url, revision, directory)
        repo, err = git.PlainClone(directory, false, &git.CloneOptions{
            URL:               url,
            Depth: 1,
            // Branch       ReferenceName: plumbing.ReferenceName("refs/heads/" + revision),
            ReferenceName: plumbing.NewTagReferenceName(revision),
        })
    }

    // Verify if any error occurred
    CheckIfError(err)

    // ... retrieving the branch being pointed by HEAD
    ref, err := repo.Head()
    CheckIfError(err)

    // ... retrieving the commit object
    commit, err := repo.CommitObject(ref.Hash())
    CheckIfError(err)

    fmt.Println(commit)
}