kustomize: Restore empty dir build

Signed-off-by: Stefan Prodan <stefan.prodan@gmail.com>

kustomize/kustomize_generator.go

@@ -26,7 +26,7 @@ import (
 	"strings"
 	"sync"
 
-	securefs "github.com/fluxcd/pkg/kustomize/filesys"
+	"github.com/hashicorp/go-multierror"
 	apiextensionsv1 "k8s.io/apiextensions-apiserver/pkg/apis/apiextensions/v1"
 	"k8s.io/apimachinery/pkg/apis/meta/v1/unstructured"
 	"k8s.io/apimachinery/pkg/runtime"
@@ -39,7 +39,7 @@ import (
 	"sigs.k8s.io/yaml"
 
 	"github.com/fluxcd/pkg/apis/kustomize"
-	"github.com/hashicorp/go-multierror"
+	securefs "github.com/fluxcd/pkg/kustomize/filesys"
 )
 
 const (
@@ -467,7 +467,14 @@ func (g *Generator) generateKustomization(dirPath string) (Action, string, error
 		resources = append(resources, strings.Replace(file, abs, ".", 1))
 	}
 
-	kus.Resources = resources
+	if len(resources) == 0 {
+		// if there are no resources, set a placeholder namespace
+		// to avoid "kustomization.yaml is empty" build error
+		kus.Namespace = "_placeholder"
+	} else {
+		kus.Resources = resources
+	}
+
 	kd, err := yaml.Marshal(kus)
 	if err != nil {
 		// delete the kustomization file

kustomize/kustomize_generator_test.go

@@ -23,18 +23,42 @@ import (
 	"strings"
 	"testing"
 
-	"github.com/fluxcd/pkg/kustomize"
 	. "github.com/onsi/gomega"
 	"github.com/otiai10/copy"
 	"k8s.io/apimachinery/pkg/apis/meta/v1/unstructured"
 	"sigs.k8s.io/kustomize/api/resmap"
 	kustypes "sigs.k8s.io/kustomize/api/types"
 	"sigs.k8s.io/kustomize/kyaml/filesys"
 	"sigs.k8s.io/yaml"
+
+	"github.com/fluxcd/pkg/kustomize"
 )
 
 const resourcePath = "./testdata/resources/"
 
+func TestGenerator_EmptyDir(t *testing.T) {
+	g := NewWithT(t)
+	dataKS, err := os.ReadFile("./testdata/empty/ks.yaml")
+	g.Expect(err).NotTo(HaveOccurred())
+
+	ks, err := readYamlObjects(strings.NewReader(string(dataKS)))
+	g.Expect(err).NotTo(HaveOccurred())
+
+	emptyDir, err := testTempDir(t)
+	g.Expect(err).NotTo(HaveOccurred())
+
+	_, err = kustomize.NewGenerator("", ks[0]).WriteFile(emptyDir)
+	g.Expect(err).NotTo(HaveOccurred())
+
+	data, err := os.ReadFile(filepath.Join(emptyDir, "kustomization.yaml"))
+	g.Expect(err).NotTo(HaveOccurred())
+	g.Expect(string(data)).To(ContainSubstring("_placeholder"))
+
+	resMap, err := kustomize.SecureBuild(emptyDir, emptyDir, false)
+	g.Expect(err).NotTo(HaveOccurred())
+	g.Expect(resMap.Resources()).To(HaveLen(0))
+}
+
 func TestKustomizationGenerator(t *testing.T) {
 	tests := []struct {
 		name    string

kustomize/testdata/empty/ks.yaml

@@ -0,0 +1,13 @@
+---
+apiVersion: kustomize.toolkit.fluxcd.io/v1
+kind: Kustomization
+metadata:
+  name: app
+  namespace: apps
+spec:
+  interval: 4m0s
+  path: ./empty
+  prune: true
+  sourceRef:
+    kind: GitRepository
+    name: app