Merge pull request kubernetes#55689 from luksa/kubectl_explain_kind_v…

…ersion

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Make kubectl explain print the Kind and APIVersion of the resource

**What this PR does / why we need it**:
Kubectl explain currently doesn't print out the Kind and APIversion of the resource being explained. When running `kubectl explain hpa.spec`, for example, there is no way of knowing whether you're looking at the `autoscaling/v1` or the `autoscaling/v2beta1` version. 
Also, `kubectl explain` is often used as a reference when writing YAML/JSON object manifests. It allows you to look up everything except the API version. Currently, you either need to know the API Version of a resource by heart or look it up in the online API docs. 
This PR fixes both problems by having `kubectl explain` print out the full Kind and APIVersion of the resource it is explaining.

Here are a few examples of the new output:
```
$ kubectl explain deploy
KIND:     Deployment
VERSION:  extensions/v1beta1

DESCRIPTION:
...


$ kubectl explain hpa.spec
KIND:     HorizontalPodAutoscaler
VERSION:  autoscaling/v1

RESOURCE: spec <Object>

DESCRIPTION:
...


$ kubectl explain hpa.spec.maxReplicas
KIND:     HorizontalPodAutoscaler
VERSION:  autoscaling/v1

FIELD:    maxReplicas <integer>

DESCRIPTION:
...


$ kubectl explain hpa.spec --recursive
KIND:     HorizontalPodAutoscaler
VERSION:  autoscaling/v1

RESOURCE: spec <Object>

DESCRIPTION:
     behaviour of autoscaler. More info:
     https://git.k8s.io/community/contributors/devel/api-conventions.md#spec-and-status.

     specification of a horizontal pod autoscaler.

FIELDS:
   maxReplicas	<integer>
   minReplicas	<integer>
   scaleTargetRef	<Object>
      apiVersion	<string>
      kind	<string>
      name	<string>
   targetCPUUtilizationPercentage	<integer>
```

**Release note**:

```release-note
Kubectl explain now prints out the Kind and API version of the resource being explained
```

pkg/kubectl/cmd/explain.go

@@ -129,5 +129,5 @@ func RunExplain(f cmdutil.Factory, out, cmdErr io.Writer, cmd *cobra.Command, ar
 		return fmt.Errorf("Couldn't find resource for %q", gvk)
 	}
 
-	return explain.PrintModelDescription(fieldsPath, out, schema, recursive)
+	return explain.PrintModelDescription(fieldsPath, out, schema, gvk, recursive)
 }

pkg/kubectl/explain/BUILD

@@ -16,6 +16,7 @@ go_library(
     visibility = ["//visibility:public"],
     deps = [
         "//vendor/k8s.io/apimachinery/pkg/api/meta:go_default_library",
+        "//vendor/k8s.io/apimachinery/pkg/runtime/schema:go_default_library",
         "//vendor/k8s.io/kube-openapi/pkg/util/proto:go_default_library",
     ],
 )

pkg/kubectl/explain/explain.go

@@ -21,6 +21,7 @@ import (
 	"strings"
 
 	"k8s.io/apimachinery/pkg/api/meta"
+	"k8s.io/apimachinery/pkg/runtime/schema"
 	"k8s.io/kube-openapi/pkg/util/proto"
 )
 
@@ -51,7 +52,7 @@ func SplitAndParseResourceRequest(inResource string, mapper meta.RESTMapper) (st
 // PrintModelDescription prints the description of a specific model or dot path.
 // If recursive, all components nested within the fields of the schema will be
 // printed.
-func PrintModelDescription(fieldsPath []string, w io.Writer, schema proto.Schema, recursive bool) error {
+func PrintModelDescription(fieldsPath []string, w io.Writer, schema proto.Schema, gvk schema.GroupVersionKind, recursive bool) error {
 	fieldName := ""
 	if len(fieldsPath) != 0 {
 		fieldName = fieldsPath[len(fieldsPath)-1]
@@ -64,5 +65,5 @@ func PrintModelDescription(fieldsPath []string, w io.Writer, schema proto.Schema
 	}
 	b := fieldsPrinterBuilder{Recursive: recursive}
 	f := &Formatter{Writer: w, Wrap: 80}
-	return PrintModel(fieldName, f, b, schema)
+	return PrintModel(fieldName, f, b, schema, gvk)
 }

pkg/kubectl/explain/model_printer.go

@@ -16,7 +16,10 @@ limitations under the License.
 
 package explain
 
-import "k8s.io/kube-openapi/pkg/util/proto"
+import (
+	"k8s.io/apimachinery/pkg/runtime/schema"
+	"k8s.io/kube-openapi/pkg/util/proto"
+)
 
 // fieldIndentLevel is the level of indentation for fields.
 const fieldIndentLevel = 3
@@ -33,11 +36,19 @@ type modelPrinter struct {
 	Descriptions []string
 	Writer       *Formatter
 	Builder      fieldsPrinterBuilder
+	GVK          schema.GroupVersionKind
 	Error        error
 }
 
 var _ proto.SchemaVisitor = &modelPrinter{}
 
+func (m *modelPrinter) PrintKindAndVersion() error {
+	if err := m.Writer.Write("KIND:     %s", m.GVK.Kind); err != nil {
+		return err
+	}
+	return m.Writer.Write("VERSION:  %s\n", m.GVK.GroupVersion())
+}
+
 // PrintDescription prints the description for a given schema. There
 // might be multiple description, since we collect descriptions when we
 // go through references, arrays and maps.
@@ -73,6 +84,11 @@ func (m *modelPrinter) VisitArray(a *proto.Array) {
 
 // VisitKind prints a full resource with its fields.
 func (m *modelPrinter) VisitKind(k *proto.Kind) {
+	if err := m.PrintKindAndVersion(); err != nil {
+		m.Error = err
+		return
+	}
+
 	if m.Type == "" {
 		m.Type = GetTypeName(k)
 	}
@@ -103,10 +119,15 @@ func (m *modelPrinter) VisitMap(om *proto.Map) {
 
 // VisitPrimitive prints a field type and its description.
 func (m *modelPrinter) VisitPrimitive(p *proto.Primitive) {
+	if err := m.PrintKindAndVersion(); err != nil {
+		m.Error = err
+		return
+	}
+
 	if m.Type == "" {
 		m.Type = GetTypeName(p)
 	}
-	if err := m.Writer.Write("FIELD: %s <%s>\n", m.Name, m.Type); err != nil {
+	if err := m.Writer.Write("FIELD:    %s <%s>\n", m.Name, m.Type); err != nil {
 		m.Error = err
 		return
 	}
@@ -120,8 +141,8 @@ func (m *modelPrinter) VisitReference(r proto.Reference) {
 }
 
 // PrintModel prints the description of a schema in writer.
-func PrintModel(name string, writer *Formatter, builder fieldsPrinterBuilder, schema proto.Schema) error {
-	m := &modelPrinter{Name: name, Writer: writer, Builder: builder}
+func PrintModel(name string, writer *Formatter, builder fieldsPrinterBuilder, schema proto.Schema, gvk schema.GroupVersionKind) error {
+	m := &modelPrinter{Name: name, Writer: writer, Builder: builder, GVK: gvk}
 	schema.Accept(m)
 	return m.Error
 }

pkg/kubectl/explain/model_printer_test.go

@@ -24,11 +24,12 @@ import (
 )
 
 func TestModel(t *testing.T) {
-	schema := resources.LookupResource(schema.GroupVersionKind{
+	gvk := schema.GroupVersionKind{
 		Group:   "",
 		Version: "v1",
 		Kind:    "OneKind",
-	})
+	}
+	schema := resources.LookupResource(gvk)
 	if schema == nil {
 		t.Fatal("Couldn't find schema v1.OneKind")
 	}
@@ -38,7 +39,10 @@ func TestModel(t *testing.T) {
 		want string
 	}{
 		{
-			want: `DESCRIPTION:
+			want: `KIND:     OneKind
+VERSION:  v1
+
+DESCRIPTION:
      OneKind has a short description
 
 FIELDS:
@@ -58,7 +62,10 @@ FIELDS:
 			path: []string{},
 		},
 		{
-			want: `RESOURCE: field1 <Object>
+			want: `KIND:     OneKind
+VERSION:  v1
+
+RESOURCE: field1 <Object>
 
 DESCRIPTION:
      Lorem ipsum dolor sit amet, consectetur adipiscing elit. Nulla ut lacus ac
@@ -90,15 +97,21 @@ FIELDS:
 			path: []string{"field1"},
 		},
 		{
-			want: `FIELD: string <string>
+			want: `KIND:     OneKind
+VERSION:  v1
+
+FIELD:    string <string>
 
 DESCRIPTION:
      This string must be a string
 `,
 			path: []string{"field1", "string"},
 		},
 		{
-			want: `FIELD: array <[]integer>
+			want: `KIND:     OneKind
+VERSION:  v1
+
+FIELD:    array <[]integer>
 
 DESCRIPTION:
      This array must be an array of int
@@ -111,7 +124,7 @@ DESCRIPTION:
 
 	for _, test := range tests {
 		buf := bytes.Buffer{}
-		if err := PrintModelDescription(test.path, &buf, schema, false); err != nil {
+		if err := PrintModelDescription(test.path, &buf, schema, gvk, false); err != nil {
 			t.Fatalf("Failed to PrintModelDescription for path %v: %v", test.path, err)
 		}
 		got := buf.String()