fix: only treat a missing branch as a new branch on clone (0.9)

internal/clients/git/git.go

@@ -42,6 +42,7 @@ var (
 	ErrEmptyRemoteRepository  = errors.New("remote repository is empty")
 	ErrAuthenticationRequired = errors.New("authentication required")
 	ErrAuthorizationFailed    = errors.New("authorization failed")
+	ErrBranchNotFound         = errors.New("branch not found")
 	NoErrAlreadyUpToDate      = git.NoErrAlreadyUpToDate
 )
 
@@ -191,7 +192,7 @@ func GetLatestCommitRemote(opts ListOptions) (*string, error) {
 		}
 	}
 
-	return nil, fmt.Errorf("Branch %s reference %s not found on remote %s", opts.Branch, repoRef, opts.URL)
+	return nil, fmt.Errorf("%w: branch %s reference %s not found on remote %s", ErrBranchNotFound, opts.Branch, repoRef, opts.URL)
 }
 
 func restoreUnsupportedCapabilities(oldUnsupportedCaps []capability.Capability) {
@@ -390,6 +391,9 @@ func Clone(opts CloneOptions) (*Repo, error) {
 		GitCookies: opts.GitCookies,
 	})
 	if err != nil {
+		if !errors.Is(err, ErrBranchNotFound) {
+			return nil, fmt.Errorf("failed to inspect remote branch: %w", err)
+		}
 		cloneOpts = git.CloneOptions{
 			RemoteName:      "origin",
 			URL:             opts.URL,

internal/clients/git/git_test.go

@@ -1,8 +1,16 @@
 package git
 
 import (
+	"errors"
+	"net/http"
+	"net/http/cgi"
+	"net/http/httptest"
 	"os"
+	"os/exec"
 	"path"
+	"path/filepath"
+	"strings"
+	"sync/atomic"
 	"testing"
 
 	"github.com/go-git/go-git/v5"
@@ -361,3 +369,55 @@ func TestCommitPreservesFileMode(t *testing.T) {
 		assert.Equal(t, filemode.Executable, entry.Mode, name)
 	}
 }
+
+func TestGetLatestCommitRemoteBranchNotFound(t *testing.T) {
+	baseRepo := BaseSuite{}
+	baseRepo.BuildBasicRepository()
+
+	_, err := GetLatestCommitRemote(ListOptions{
+		URL:    baseRepo.GetBasicLocalRepositoryURL(),
+		Branch: "missing-branch",
+	})
+	require.Error(t, err)
+	assert.True(t, errors.Is(err, ErrBranchNotFound))
+}
+
+// A failed branch lookup that is not "branch not found" must not be treated as a new branch:
+// that path empties the worktree, so the next commit would delete every existing file.
+func TestCloneFailsOnTransientBranchLookupError(t *testing.T) {
+	gitExecPath, err := exec.Command("git", "--exec-path").Output()
+	if err != nil {
+		t.Skip("git not available")
+	}
+
+	baseRepo := BaseSuite{}
+	baseRepo.BuildBasicRepository()
+	dotGit := baseRepo.GetBasicLocalRepositoryURL()
+
+	backend := &cgi.Handler{
+		Path: filepath.Join(strings.TrimSpace(string(gitExecPath)), "git-http-backend"),
+		Env: []string{
+			"GIT_PROJECT_ROOT=" + filepath.Dir(dotGit),
+			"GIT_HTTP_EXPORT_ALL=1",
+		},
+	}
+	var calls atomic.Int32
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if calls.Add(1) == 1 {
+			http.Error(w, "unavailable", http.StatusServiceUnavailable)
+			return
+		}
+		backend.ServeHTTP(w, r)
+	}))
+	defer srv.Close()
+
+	repo, err := Clone(CloneOptions{
+		URL:    srv.URL + "/" + filepath.Base(dotGit),
+		Branch: "master",
+	})
+	if repo != nil {
+		defer repo.Cleanup()
+	}
+	require.Error(t, err)
+	assert.False(t, errors.Is(err, ErrBranchNotFound))
+}