diff: ignore kind and apiVersion when diffing

Author: chrischdi

pkg/util/diff.go

@@ -18,6 +18,7 @@ package util
 import (
 	"errors"
 	"fmt"
+	"reflect"
 	"sort"
 	"strings"
 
@@ -129,6 +130,10 @@ func (d *differ) Diff(a, b client.Object) (DiffResult, error) {
 		return nil, errObjectsToCompareCannotBeNil
 	}
 
+	if reflect.TypeOf(a) != reflect.TypeOf(b) {
+		return nil, fmt.Errorf("objects to diff are not of the same type: %T != %T", a, b)
+	}
+
 	// 1. Convert the objects to unstructured.
 	unstructuredA, err := runtime.DefaultUnstructuredConverter.ToUnstructured(a)
 	if err != nil {
@@ -196,6 +201,10 @@ func (d *differ) Diff(a, b client.Object) (DiffResult, error) {
 // NewDefaultDiffer creates a new default differ with the default options.
 func NewDefaultDiffer(opts ...diffopts) *differ {
 	return newDiffer(append(opts,
+		// Always ignore kind and apiVersion as they may not be always set. Instead the differ checks if the input objects have the same type.
+		WithIgnoreField("kind"),
+		WithIgnoreField("apiVersion"),
+
 		// Options for handling of metadata fields.
 
 		// Special handling for Cluster API's conversion-data label.

pkg/util/diff_test.go

@@ -18,11 +18,22 @@ package util
 import (
 	. "github.com/onsi/ginkgo/v2"
 	. "github.com/onsi/gomega"
+	mapiv1beta1 "github.com/openshift/api/machine/v1beta1"
 	"k8s.io/apimachinery/pkg/apis/meta/v1/unstructured"
 )
 
 var _ = Describe("Unit test Diff", func() {
 
+	Describe("error cases", func() {
+		It("should return an error if the objects are not of the same type", func() {
+			a := &mapiv1beta1.MachineSet{}
+			b := &mapiv1beta1.Machine{}
+			_, err := NewDefaultDiffer().Diff(a, b)
+			Expect(err).To(HaveOccurred())
+			Expect(err).To(MatchError(ContainSubstring("objects to diff are not of the same type")))
+		})
+	})
+
 	type testInput struct {
 		a           unstructured.Unstructured
 		b           unstructured.Unstructured