Prevent panic when cloning empty git repository

This covers the edge case in which a user creates a GitRepository CR
referencing an empty Git repository. Currently, the controller will panic
in this situation since the returned commit pointer is nil.

Signed-off-by: Aurel Canciu <aurelcanciu@gmail.com>

controllers/gitrepository_controller.go

@@ -61,6 +61,10 @@ import (
 	"github.com/fluxcd/source-controller/internal/util"
 )
 
+// EmptyGitRepositoryReason signals that a referenced Git repository is empty
+// (only has an initial branch without any commits).
+const EmptyGitRepositoryReason string = "EmptyGitRepository"
+
 // gitRepositoryReadyCondition contains the information required to summarize a
 // v1beta2.GitRepository Ready Condition.
 var gitRepositoryReadyCondition = summarize.Conditions{
@@ -537,6 +541,14 @@ func (r *GitRepositoryReconciler) reconcileSource(ctx context.Context, sp *patch
 	if err != nil {
 		return sreconcile.ResultEmpty, err
 	}
+	if c == nil {
+		e := serror.NewGeneric(
+			fmt.Errorf("git repository is empty"),
+			EmptyGitRepositoryReason,
+		)
+		conditions.MarkTrue(obj, sourcev1.FetchFailedCondition, e.Reason, e.Err.Error())
+		return sreconcile.ResultEmpty, e
+	}
 	// Assign the commit to the shared commit reference.
 	*commit = *c
 

controllers/gitrepository_controller_test.go

@@ -220,6 +220,65 @@ func TestGitRepositoryReconciler_Reconcile(t *testing.T) {
 	testSuspendedObjectDeleteWithArtifact(ctx, g, obj)
 }
 
+func TestGitRepositoryReconciler_reconcileSource_emptyRepository(t *testing.T) {
+	g := NewWithT(t)
+
+	server, err := gittestserver.NewTempGitServer()
+	g.Expect(err).NotTo(HaveOccurred())
+	defer os.RemoveAll(server.Root())
+	server.AutoCreate()
+	g.Expect(server.StartHTTP()).To(Succeed())
+	defer server.StopHTTP()
+
+	obj := &sourcev1.GitRepository{
+		ObjectMeta: metav1.ObjectMeta{
+			GenerateName: "empty-",
+			Generation:   1,
+		},
+		Spec: sourcev1.GitRepositorySpec{
+			Interval: metav1.Duration{Duration: interval},
+			Timeout:  &metav1.Duration{Duration: timeout},
+			URL:      server.HTTPAddress() + "/test.git",
+		},
+	}
+
+	fs := memfs.New()
+	localRepo, err := gogit.Init(memory.NewStorage(), fs)
+	g.Expect(err).NotTo(HaveOccurred())
+
+	builder := fakeclient.NewClientBuilder().WithScheme(testEnv.GetScheme())
+
+	r := &GitRepositoryReconciler{
+		Client:        builder.Build(),
+		EventRecorder: record.NewFakeRecorder(32),
+		Storage:       testStorage,
+		patchOptions:  getPatchOptions(gitRepositoryReadyCondition.Owned, "sc"),
+	}
+
+	tmpDir := t.TempDir()
+
+	head, _ := localRepo.Head()
+	g.Expect(head).To(BeNil())
+
+	g.Expect(r.Client.Create(context.TODO(), obj)).ToNot(HaveOccurred())
+	defer func() {
+		g.Expect(r.Client.Delete(context.TODO(), obj)).ToNot(HaveOccurred())
+	}()
+
+	var commit git.Commit
+	var includes artifactSet
+	sp := patch.NewSerialPatcher(obj, r.Client)
+
+	got, err := r.reconcileSource(context.TODO(), sp, obj, &commit, &includes, tmpDir)
+	assertConditions := []metav1.Condition{
+		*conditions.TrueCondition(sourcev1.FetchFailedCondition, EmptyGitRepositoryReason, "git repository is empty"),
+	}
+	g.Expect(obj.Status.Conditions).To(conditions.MatchConditions(assertConditions))
+	g.Expect(err).To(HaveOccurred())
+	g.Expect(got).To(Equal(sreconcile.ResultEmpty))
+	g.Expect(commit).ToNot(BeNil())
+}
+
 func TestGitRepositoryReconciler_reconcileSource_authStrategy(t *testing.T) {
 	type options struct {
 		username   string