pkg/vcs: support fetches by a short git hash

The approach we used works perfectly for all commits, but they must be
referenced by the full 40 character hash. In almost all cases, users
would prefer to use the shorter one.

If the commit hash is not 40 characters long, fetch the whole git tree.

The only unsupported scenario is fetching a commit that is referenced by
custom refs/* by its short hash. It's unlikely there's anything we can
do here.

1 files changed, 19 insertions, 0 deletions

diff --git a/pkg/vcs/git_test.go b/pkg/vcs/git_test.go
index 5e9d30fa7..73670dd4a 100644
--- a/pkg/vcs/git_test.go
+++ b/pkg/vcs/git_test.go
@@ -426,3 +426,22 @@ func TestGitRemoteTags(t *testing.T) {
 	sort.Strings(tags)
 	assert.Equal(t, []string{"v1.0", "v2.0"}, tags)
 }
+
+func TestGitFetchShortHash(t *testing.T) {
+	remoteRepoDir := t.TempDir()
+	remote := MakeTestRepo(t, remoteRepoDir)
+	remote.Git("commit", "--no-edit", "--allow-empty", "-m", "base commit")
+	remote.Git("checkout", "-b", "base_branch")
+	remote.Git("tag", "base_tag")
+	remote.Git("checkout", "-b", "temp_branch")
+	remote.Git("commit", "--no-edit", "--allow-empty", "-m", "detached commit")
+	refCommit, _ := remote.repo.HeadCommit()
+
+	// Create a local repo.
+	localRepoDir := t.TempDir()
+	local := newGit(localRepoDir, nil, nil)
+
+	// Fetch the commit from the custom ref.
+	_, err := local.CheckoutCommit(remoteRepoDir, refCommit.Hash[:12])
+	assert.NoError(t, err)
+}