pkg/vcs: make git fetch calls more specific

This should make syzkaller only fetch the commits relevant for further
processing. Also, specifying the exact commit/branch name to fetch
allows us to access commits from custom refs.

Test the new behaviour and double-check that remote tags fetch was not
broken.

1 files changed, 7 insertions, 3 deletions

diff --git a/pkg/vcs/git.go b/pkg/vcs/git.go
index 71fcac97a..0bd72d9a6 100644
--- a/pkg/vcs/git.go
+++ b/pkg/vcs/git.go
@@ -134,17 +134,21 @@ func (git *git) CheckoutCommit(repo, commit string) (*Commit, error) {
 	if err := git.repair(); err != nil {
 		return nil, err
 	}
-	if err := git.fetchRemote(repo); err != nil {
+	if err := git.fetchRemote(repo, commit); err != nil {
 		return nil, err
 	}
 	return git.SwitchCommit(commit)
 }
 
-func (git *git) fetchRemote(repo string) error {
+func (git *git) fetchRemote(repo, commit string) error {
 	repoHash := hash.String([]byte(repo))
 	// Ignore error as we can double add the same remote and that will fail.
 	git.git("remote", "add", repoHash, repo)
-	_, err := git.git("fetch", "--force", "--tags", repoHash)
+	fetchArgs := []string{"fetch", "--force", "--tags", repoHash}
+	if commit != "" {
+		fetchArgs = append(fetchArgs, commit)
+	}
+	_, err := git.git(fetchArgs...)
 	if err != nil {
 		var verbose *osutil.VerboseError
 		if errors.As(err, &verbose) &&