fix(engine): log debug warning when lookup returns no object

Signed-off-by: texasich <texasich@users.noreply.github.com>

pkg/engine/engine_test.go

@@ -17,8 +17,10 @@ limitations under the License.
 package engine
 
 import (
+	"bytes"
 	"errors"
 	"fmt"
+	"log/slog"
 	"path"
 	"strings"
 	"sync"
@@ -393,6 +395,51 @@ func TestRenderWithClientProvider(t *testing.T) {
 	}
 }
 
+func TestLookupLogsDebugWhenObjectNotFound(t *testing.T) {
+	provider := &testClientProvider{
+		t: t,
+		scheme: map[string]kindProps{
+			"v1/Namespace": {
+				gvr: schema.GroupVersionResource{
+					Version:  "v1",
+					Resource: "namespaces",
+				},
+			},
+		},
+		objects: []runtime.Object{
+			makeUnstructured("v1", "Namespace", "default", ""),
+		},
+	}
+
+	originalLogger := slog.Default()
+	logBuffer := &bytes.Buffer{}
+	slog.SetDefault(slog.New(slog.NewTextHandler(logBuffer, &slog.HandlerOptions{Level: slog.LevelDebug})))
+	t.Cleanup(func() {
+		slog.SetDefault(originalLogger)
+	})
+
+	lookup := newLookupFunction(provider)
+
+	_, err := lookup("v1", "Namespace", "", "absent")
+	if err != nil {
+		t.Fatalf("expected no error when lookup object is missing: %v", err)
+	}
+
+	logOutput := logBuffer.String()
+	if !strings.Contains(logOutput, "lookup returned no object") {
+		t.Fatalf("expected debug log for missing lookup object, got: %q", logOutput)
+	}
+
+	logBuffer.Reset()
+	_, err = lookup("v1", "Namespace", "", "default")
+	if err != nil {
+		t.Fatalf("expected no error when lookup object exists: %v", err)
+	}
+	if strings.Contains(logBuffer.String(), "lookup returned no object") {
+		t.Fatalf("did not expect missing-object debug log for existing lookup object, got: %q", logBuffer.String())
+	}
+}
+
 func TestRenderWithClientProvider_error(t *testing.T) {
 	c := &chart.Chart{
 		Metadata: &chart.Metadata{

pkg/engine/funcs.go

@@ -21,6 +21,7 @@ import (
 	"encoding/json"
 	"errors"
 	"fmt"
+	"log/slog"
 	"maps"
 	"math"
 	"reflect"
@@ -89,7 +90,8 @@ func funcMap() template.FuncMap {
 		"required": func(string, any) (any, error) { return "not implemented", nil },
 		// Provide a placeholder for the "lookup" function, which requires a kubernetes
 		// connection.
-		"lookup": func(string, string, string, string) (map[string]any, error) {
+		"lookup": func(apiVersion, kind, namespace, name string) (map[string]any, error) {
+			slog.Debug("lookup skipped: no Kubernetes client available", "apiVersion", apiVersion, "kind", kind, "namespace", namespace, "name", name)
 			return map[string]any{}, nil
 		},
 	}

pkg/engine/funcs_test.go

@@ -17,6 +17,8 @@ limitations under the License.
 package engine
 
 import (
+	"bytes"
+	"log/slog"
 	"math"
 	"strings"
 	"testing"
@@ -195,6 +197,26 @@ keyInElement1 = "valueInElement1"`,
 	}
 }
 
+func TestLookupPlaceholderLogsDebug(t *testing.T) {
+	originalLogger := slog.Default()
+	logBuffer := &bytes.Buffer{}
+	slog.SetDefault(slog.New(slog.NewTextHandler(logBuffer, &slog.HandlerOptions{Level: slog.LevelDebug})))
+	t.Cleanup(func() {
+		slog.SetDefault(originalLogger)
+	})
+
+	var output strings.Builder
+	err := template.Must(template.New("test").Funcs(funcMap()).Parse(`{{ lookup "v1" "Namespace" "" "missing" }}`)).Execute(&output, nil)
+	require.NoError(t, err)
+	assert.Equal(t, "map[]", output.String())
+
+	logOutput := logBuffer.String()
+	assert.Contains(t, logOutput, "lookup skipped: no Kubernetes client available")
+	assert.Contains(t, logOutput, "apiVersion=v1")
+	assert.Contains(t, logOutput, "kind=Namespace")
+	assert.Contains(t, logOutput, "name=missing")
+}
+
 func TestDurationHelpers(t *testing.T) {
 	tests := []struct {
 		name   string

pkg/engine/lookup_func.go

@@ -73,6 +73,7 @@ func newLookupFunction(clientProvider ClientProvider) lookupFunc {
 				if apierrors.IsNotFound(err) {
 					// Just return an empty interface when the object was not found.
 					// That way, users can use `if not (lookup ...)` in their templates.
+					slog.Debug("lookup returned no object", "apiVersion", apiversion, "kind", kind, "namespace", namespace, "name", name)
 					return map[string]any{}, nil
 				}
 				return map[string]any{}, err
@@ -85,6 +86,7 @@ func newLookupFunction(clientProvider ClientProvider) lookupFunc {
 			if apierrors.IsNotFound(err) {
 				// Just return an empty interface when the object was not found.
 				// That way, users can use `if not (lookup ...)` in their templates.
+				slog.Debug("lookup returned no objects", "apiVersion", apiversion, "kind", kind, "namespace", namespace)
 				return map[string]any{}, nil
 			}
 			return map[string]any{}, err