replace KObjs with KObjSlice

KObjSlice can be used in log calls without causing unnecessary work when the
log event does not get logged.

examples/benchmarks/benchmarks_test.go

@@ -75,7 +75,7 @@ func BenchmarkOutput(b *testing.B) {
 		tests = append(tests, testcase{
 			name: fmt.Sprintf("objects/%d", length),
 			generate: func() interface{} {
-				return klog.KObjs(arg)
+				return klog.KObjSlice(arg)
 			},
 		})
 	}

k8s_references.go

@@ -77,6 +77,8 @@ func KRef(namespace, name string) ObjectRef {
 }
 
 // KObjs returns slice of ObjectRef from an slice of ObjectMeta
+//
+// DEPRECATED: Use KObjSlice instead, it has better performance.
 func KObjs(arg interface{}) []ObjectRef {
 	s := reflect.ValueOf(arg)
 	if s.Kind() != reflect.Slice {
@@ -92,3 +94,57 @@ func KObjs(arg interface{}) []ObjectRef {
 	}
 	return objectRefs
 }
+
+// KObjSlice takes a slice of objects that implement the KMetadata interface
+// and returns an object that gets logged as a slice of ObjectRef values or a
+// string containing those values, depending on whether the logger prefers text
+// output or structured output.
+//
+// An error string is logged when KObjSlice is not passed a suitable slice.
+//
+// Processing of the argument is delayed until the value actually gets logged,
+// in contrast to KObjs where that overhead is incurred regardless of whether
+// the result is needed.
+func KObjSlice(arg interface{}) interface{} {
+	return kobjSlice{arg: arg}
+}
+
+type kobjSlice struct {
+	arg interface{}
+}
+
+var _ fmt.Stringer = kobjSlice{}
+var _ logr.Marshaler = kobjSlice{}
+
+func (ks kobjSlice) String() string {
+	objectRefs, err := ks.process()
+	if err != nil {
+		return err.Error()
+	}
+	return fmt.Sprintf("%v", objectRefs)
+}
+
+func (ks kobjSlice) MarshalLog() interface{} {
+	objectRefs, err := ks.process()
+	if err != nil {
+		return err.Error()
+	}
+	return objectRefs
+}
+
+func (ks kobjSlice) process() ([]ObjectRef, error) {
+	s := reflect.ValueOf(ks.arg)
+	if s.Kind() != reflect.Slice {
+		return nil, fmt.Errorf("<KObjSlice needs a slice, got type %T>", ks.arg)
+	}
+	objectRefs := make([]ObjectRef, 0, s.Len())
+	for i := 0; i < s.Len(); i++ {
+		item := s.Index(i).Interface()
+		if v, ok := item.(KMetadata); ok {
+			objectRefs = append(objectRefs, KObj(v))
+		} else {
+			return nil, fmt.Errorf("<KObjSlice needs a slice of values implementing KMetadata, got type %T>", item)
+		}
+	}
+	return objectRefs, nil
+}

test/output.go

@@ -268,6 +268,40 @@ I output.go:<LINE>] "test" firstKey=1 secondKey=3
 					&kmeta{Name: "pod-2", Namespace: "kube-system"},
 				})},
 			expectedOutput: `I output.go:<LINE>] "test" pods=[kube-system/pod-1 kube-system/pod-2]
+`,
+		},
+		"KObjSlice okay": {
+			text: "test",
+			values: []interface{}{"pods",
+				klog.KObjSlice([]interface{}{
+					&kmeta{Name: "pod-1", Namespace: "kube-system"},
+					&kmeta{Name: "pod-2", Namespace: "kube-system"},
+				})},
+			expectedOutput: `I output.go:<LINE>] "test" pods="[kube-system/pod-1 kube-system/pod-2]"
+`,
+		},
+		"KObjSlice nil arg": {
+			text: "test",
+			values: []interface{}{"pods",
+				klog.KObjSlice(nil)},
+			expectedOutput: `I output.go:<LINE>] "test" pods="<KObjSlice needs a slice, got type <nil>>"
+`,
+		},
+		"KObjSlice nil entry": {
+			text: "test",
+			values: []interface{}{"pods",
+				klog.KObjSlice([]interface{}{
+					&kmeta{Name: "pod-1", Namespace: "kube-system"},
+					nil,
+				})},
+			expectedOutput: `I output.go:<LINE>] "test" pods="<KObjSlice needs a slice of values implementing KMetadata, got type <nil>>"
+`,
+		},
+		"KObjSlice ints": {
+			text: "test",
+			values: []interface{}{"ints",
+				klog.KObjSlice([]int{1, 2, 3})},
+			expectedOutput: `I output.go:<LINE>] "test" ints="<KObjSlice needs a slice of values implementing KMetadata, got type int>"
 `,
 		},
 		"regular error types as value": {

test/zapr.go

@@ -67,6 +67,22 @@ func ZaprOutputMappingDirect() map[string]string {
 
 		`I output.go:<LINE>] "test" pods=[kube-system/pod-1 kube-system/pod-2]
 `: `{"caller":"test/output.go:<LINE>","msg":"test","v":0,"pods":[{"name":"pod-1","namespace":"kube-system"},{"name":"pod-2","namespace":"kube-system"}]}
+`,
+
+		`I output.go:<LINE>] "test" pods="[kube-system/pod-1 kube-system/pod-2]"
+`: `{"caller":"test/output.go:<LINE>","msg":"test","v":0,"pods":[{"name":"pod-1","namespace":"kube-system"},{"name":"pod-2","namespace":"kube-system"}]}
+`,
+
+		`I output.go:<LINE>] "test" pods="<KObjSlice needs a slice, got type <nil>>"
+`: `{"caller":"test/output.go:<LINE>","msg":"test","v":0,"pods":"<KObjSlice needs a slice, got type <nil>>"}
+`,
+
+		`I output.go:<LINE>] "test" ints="<KObjSlice needs a slice of values implementing KMetadata, got type int>"
+`: `{"caller":"test/output.go:<LINE>","msg":"test","v":0,"ints":"<KObjSlice needs a slice of values implementing KMetadata, got type int>"}
+`,
+
+		`I output.go:<LINE>] "test" pods="<KObjSlice needs a slice of values implementing KMetadata, got type <nil>>"
+`: `{"caller":"test/output.go:<LINE>","msg":"test","v":0,"pods":"<KObjSlice needs a slice of values implementing KMetadata, got type <nil>>"}
 `,
 
 		`I output.go:<LINE>] "test" akey="avalue"