Emit a warning when deprecated fields are used

api/internal/target/kusttarget.go

@@ -6,6 +6,7 @@ package target
 import (
 	"encoding/json"
 	"fmt"
+	"os"
 	"strings"
 
 	"github.com/pkg/errors"
@@ -69,6 +70,15 @@ func (kt *KustTarget) Load() error {
 	if err != nil {
 		return err
 	}
+
+	// show warning message when using deprecated fields.
+	warningMessages := k.CheckDeprecatedFields()
+	if warningMessages != nil {
+		for _, msg := range *warningMessages {
+			fmt.Fprintf(os.Stderr, "%v\n", msg)
+		}
+	}
+
 	k.FixKustomizationPostUnmarshalling()
 	errs := k.EnforceFields()
 	if len(errs) > 0 {

api/types/kustomization.go

@@ -59,12 +59,14 @@ type Kustomization struct {
 	// CommonAnnotations to add to all objects.
 	CommonAnnotations map[string]string `json:"commonAnnotations,omitempty" yaml:"commonAnnotations,omitempty"`
 
+	// Deprecated: Use the Patches field instead, which provides a superset of the functionality of PatchesStrategicMerge.
 	// PatchesStrategicMerge specifies the relative path to a file
 	// containing a strategic merge patch.  Format documented at
 	// https://github.com/kubernetes/community/blob/master/contributors/devel/sig-api-machinery/strategic-merge-patch.md
 	// URLs and globs are not supported.
 	PatchesStrategicMerge []PatchStrategicMerge `json:"patchesStrategicMerge,omitempty" yaml:"patchesStrategicMerge,omitempty"`
 
+	// Deprecated: Use the Patches field instead, which provides a superset of the functionality of JSONPatches.
 	// JSONPatches is a list of JSONPatch for applying JSON patch.
 	// Format documented at https://tools.ietf.org/html/rfc6902
 	// and http://jsonpatch.com
@@ -88,6 +90,7 @@ type Kustomization struct {
 	// specification. This can also be done with a patch.
 	Replicas []Replica `json:"replicas,omitempty" yaml:"replicas,omitempty"`
 
+	// Deprecated: Vars will be removed in future release. Migrate to Replacements instead.
 	// Vars allow things modified by kustomize to be injected into a
 	// kubernetes object specification. A var is a name (e.g. FOO) associated
 	// with a field in a specific resource instance.  The field must
@@ -116,9 +119,7 @@ type Kustomization struct {
 	// CRDs themselves are not modified.
 	Crds []string `json:"crds,omitempty" yaml:"crds,omitempty"`
 
-	// Deprecated.
-	// Anything that would have been specified here should
-	// be specified in the Resources field instead.
+	// Deprecated: Anything that would have been specified here should be specified in the Resources field instead.
 	Bases []string `json:"bases,omitempty" yaml:"bases,omitempty"`
 
 	//
@@ -172,6 +173,33 @@ type Kustomization struct {
 	BuildMetadata []string `json:"buildMetadata,omitempty" yaml:"buildMetadata,omitempty"`
 }
 
+const (
+	deprecatedWarningToRunEditFix              = "Run 'kustomize edit fix' to update your Kustomization automatically."
+	deprecatedWarningToRunEditFixExperimential = "[EXPERIMENTAL] Run 'kustomize edit fix' to update your Kustomization automatically."
+	deprecatedBaseWarningMessage               = "# Warning: 'bases' is deprecated. Please use 'resources' instead." + " " + deprecatedWarningToRunEditFix
+	deprecatedPatchesJson6902Message           = "# Warning: 'patchesJson6902' is deprecated. Please use 'patches' instead." + " " + deprecatedWarningToRunEditFix
+	deprecatedPatchesStrategicMergeMessage     = "# Warning: 'patchesStrategicMerge' is deprecated. Please use 'patches' instead." + " " + deprecatedWarningToRunEditFix
+	deprecatedVarsMessage                      = "# Warning: 'vars' is deprecated. Please use 'replacements' instead." + " " + deprecatedWarningToRunEditFixExperimential
+)
+
+// CheckDeprecatedFields check deprecated field is used or not.
+func (k *Kustomization) CheckDeprecatedFields() *[]string {
+	var warningMessages []string
+	if k.Bases != nil {
+		warningMessages = append(warningMessages, deprecatedBaseWarningMessage)
+	}
+	if k.PatchesJson6902 != nil {
+		warningMessages = append(warningMessages, deprecatedPatchesJson6902Message)
+	}
+	if k.PatchesStrategicMerge != nil {
+		warningMessages = append(warningMessages, deprecatedPatchesStrategicMergeMessage)
+	}
+	if k.Vars != nil {
+		warningMessages = append(warningMessages, deprecatedVarsMessage)
+	}
+	return &warningMessages
+}
+
 // FixKustomizationPostUnmarshalling fixes things
 // like empty fields that should not be empty, or
 // moving content of deprecated fields to newer
@@ -187,8 +215,11 @@ func (k *Kustomization) FixKustomizationPostUnmarshalling() {
 			k.APIVersion = KustomizationVersion
 		}
 	}
+
+	// 'bases' field was deprecated in favor of the 'resources' field.
 	k.Resources = append(k.Resources, k.Bases...)
 	k.Bases = nil
+
 	for i, g := range k.ConfigMapGenerator {
 		if g.EnvSource != "" {
 			k.ConfigMapGenerator[i].EnvSources =

api/types/kustomization_test.go

@@ -16,6 +16,66 @@ func fixKustomizationPostUnmarshallingCheck(k, e *Kustomization) bool {
 		k.Bases == nil
 }
 
+func TestKustomization_CheckDeprecatedFields(t *testing.T) {
+	tests := []struct {
+		name string
+		k    Kustomization
+		want *[]string
+	}{
+		{
+			name: "using_bases",
+			k: Kustomization{
+				Bases: []string{"base"},
+			},
+			want: &[]string{deprecatedBaseWarningMessage},
+		},
+		{
+			name: "usingPatchesJson6902",
+			k: Kustomization{
+				PatchesJson6902: []Patch{},
+			},
+			want: &[]string{deprecatedPatchesJson6902Message},
+		},
+		{
+			name: "usingPatchesStrategicMerge",
+			k: Kustomization{
+				PatchesStrategicMerge: []PatchStrategicMerge{},
+			},
+			want: &[]string{deprecatedPatchesStrategicMergeMessage},
+		},
+		{
+			name: "usingVar",
+			k: Kustomization{
+				Vars: []Var{},
+			},
+			want: &[]string{deprecatedVarsMessage},
+		},
+		{
+			name: "usingAll",
+			k: Kustomization{
+				Bases:                 []string{"base"},
+				PatchesJson6902:       []Patch{},
+				PatchesStrategicMerge: []PatchStrategicMerge{},
+				Vars:                  []Var{},
+			},
+			want: &[]string{
+				deprecatedBaseWarningMessage,
+				deprecatedPatchesJson6902Message,
+				deprecatedPatchesStrategicMergeMessage,
+				deprecatedVarsMessage,
+			},
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			k := tt.k
+			if got := k.CheckDeprecatedFields(); !reflect.DeepEqual(got, tt.want) {
+				t.Errorf("Kustomization.CheckDeprecatedFields() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}
+
 func TestFixKustomizationPostUnmarshalling(t *testing.T) {
 	var k Kustomization
 	k.Bases = append(k.Bases, "foo")