Rewrite kubectl explain to use openapi

This removes all dependencies on swagger 1.2 for explain.

pkg/kubectl/BUILD

@@ -91,7 +91,6 @@ go_library(
         "deployment.go",
         "doc.go",
         "env_file.go",
-        "explain.go",
         "generate.go",
         "history.go",
         "interfaces.go",
@@ -118,7 +117,6 @@ go_library(
     deps = [
         "//federation/apis/federation/v1beta1:go_default_library",
         "//pkg/api:go_default_library",
-        "//pkg/api/util:go_default_library",
         "//pkg/api/v1:go_default_library",
         "//pkg/api/v1/pod:go_default_library",
         "//pkg/apis/apps:go_default_library",
@@ -142,7 +140,6 @@ go_library(
         "//pkg/kubectl/util/slice:go_default_library",
         "//pkg/printers:go_default_library",
         "//pkg/printers/internalversion:go_default_library",
-        "//vendor/github.com/emicklei/go-restful-swagger12:go_default_library",
         "//vendor/github.com/golang/glog:go_default_library",
         "//vendor/github.com/spf13/cobra:go_default_library",
         "//vendor/github.com/spf13/pflag:go_default_library",
@@ -196,6 +193,7 @@ filegroup(
         ":package-srcs",
         "//pkg/kubectl/apps:all-srcs",
         "//pkg/kubectl/cmd:all-srcs",
+        "//pkg/kubectl/explain:all-srcs",
         "//pkg/kubectl/metricsutil:all-srcs",
         "//pkg/kubectl/plugins:all-srcs",
         "//pkg/kubectl/proxy:all-srcs",

pkg/kubectl/cmd/BUILD

@@ -84,6 +84,7 @@ go_library(
         "//pkg/kubectl/cmd/util:go_default_library",
         "//pkg/kubectl/cmd/util/editor:go_default_library",
         "//pkg/kubectl/cmd/util/openapi:go_default_library",
+        "//pkg/kubectl/explain:go_default_library",
         "//pkg/kubectl/metricsutil:go_default_library",
         "//pkg/kubectl/plugins:go_default_library",
         "//pkg/kubectl/proxy:go_default_library",

pkg/kubectl/cmd/explain.go

@@ -24,9 +24,9 @@ import (
 
 	"k8s.io/apimachinery/pkg/runtime/schema"
 	"k8s.io/kubernetes/pkg/api"
-	"k8s.io/kubernetes/pkg/kubectl"
 	"k8s.io/kubernetes/pkg/kubectl/cmd/templates"
 	cmdutil "k8s.io/kubernetes/pkg/kubectl/cmd/util"
+	"k8s.io/kubernetes/pkg/kubectl/explain"
 	"k8s.io/kubernetes/pkg/kubectl/util/i18n"
 )
 
@@ -80,7 +80,7 @@ func RunExplain(f cmdutil.Factory, out, cmdErr io.Writer, cmd *cobra.Command, ar
 	// TODO: After we figured out the new syntax to separate group and resource, allow
 	// the users to use it in explain (kubectl explain <group><syntax><resource>).
 	// Refer to issue #16039 for why we do this. Refer to PR #15808 that used "/" syntax.
-	inModel, fieldsPath, err := kubectl.SplitAndParseResourceRequest(args[0], mapper)
+	inModel, fieldsPath, err := explain.SplitAndParseResourceRequest(args[0], mapper)
 	if err != nil {
 		return err
 	}
@@ -108,14 +108,20 @@ func RunExplain(f cmdutil.Factory, out, cmdErr io.Writer, cmd *cobra.Command, ar
 	} else {
 		apiVersion, err = schema.ParseGroupVersion(apiVersionString)
 		if err != nil {
-			return nil
+			return err
 		}
 	}
+	gvk = apiVersion.WithKind(gvk.Kind)
 
-	schema, err := f.SwaggerSchema(apiVersion.WithKind(gvk.Kind))
+	resources, err := f.OpenAPISchema()
 	if err != nil {
 		return err
 	}
 
-	return kubectl.PrintModelDescription(inModel, fieldsPath, out, schema, recursive)
+	schema := resources.LookupResource(gvk)
+	if schema == nil {
+		return fmt.Errorf("Couldn't find resource for %q", gvk)
+	}
+
+	return explain.PrintModelDescription(fieldsPath, out, schema, recursive)
 }

pkg/kubectl/cmd/util/openapi/openapi.go

@@ -18,6 +18,7 @@ package openapi
 
 import (
 	"fmt"
+	"sort"
 	"strings"
 
 	"k8s.io/apimachinery/pkg/runtime/schema"
@@ -181,6 +182,26 @@ func (k *Kind) GetName() string {
 	return fmt.Sprintf("Kind(%v)", properties)
 }
 
+// IsRequired returns true if `field` is a required field for this type.
+func (k *Kind) IsRequired(field string) bool {
+	for _, f := range k.RequiredFields {
+		if f == field {
+			return true
+		}
+	}
+	return false
+}
+
+// Keys returns a alphabetically sorted list of keys.
+func (k *Kind) Keys() []string {
+	keys := make([]string, 0)
+	for key := range k.Fields {
+		keys = append(keys, key)
+	}
+	sort.Strings(keys)
+	return keys
+}
+
 // Map is an object who values must all be of the same `SubType`.
 // The key of the object is always of type `string`.
 type Map struct {

pkg/kubectl/explain.go

@@ -1,251 +0,0 @@
-/*
-Copyright 2014 The Kubernetes Authors.
-
-Licensed under the Apache License, Version 2.0 (the "License");
-you may not use this file except in compliance with the License.
-You may obtain a copy of the License at
-
-    http://www.apache.org/licenses/LICENSE-2.0
-
-Unless required by applicable law or agreed to in writing, software
-distributed under the License is distributed on an "AS IS" BASIS,
-WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-See the License for the specific language governing permissions and
-limitations under the License.
-*/
-
-package kubectl
-
-import (
-	"fmt"
-	"io"
-	"strings"
-
-	"github.com/emicklei/go-restful-swagger12"
-
-	"k8s.io/apimachinery/pkg/api/meta"
-	apiutil "k8s.io/kubernetes/pkg/api/util"
-)
-
-var allModels = make(map[string]*swagger.NamedModel)
-
-// SplitAndParseResourceRequest separates the users input into a model and fields
-func SplitAndParseResourceRequest(inResource string, mapper meta.RESTMapper) (string, []string, error) {
-	inResource, fieldsPath := splitDotNotation(inResource)
-	inResource, _ = mapper.ResourceSingularizer(inResource)
-	return inResource, fieldsPath, nil
-}
-
-// 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(inModel string, fieldsPath []string, w io.Writer, swaggerSchema *swagger.ApiDeclaration, recursive bool) error {
-	apiVer := apiutil.GetVersion(swaggerSchema.ApiVersion) + "."
-
-	var pointedModel *swagger.NamedModel
-	for i := range swaggerSchema.Models.List {
-		name := swaggerSchema.Models.List[i].Name
-
-		allModels[name] = &swaggerSchema.Models.List[i]
-		if strings.ToLower(name) == strings.ToLower(apiVer+inModel) {
-			pointedModel = &swaggerSchema.Models.List[i]
-		}
-	}
-	if pointedModel == nil {
-		return fmt.Errorf("requested resource %q is not defined", inModel)
-	}
-
-	if len(fieldsPath) == 0 {
-		return printTopLevelResourceInfo(w, pointedModel, recursive)
-	}
-
-	var pointedModelAsProp *swagger.NamedModelProperty
-	for _, field := range fieldsPath {
-		if prop, nextModel, isModel := getField(pointedModel, field); prop != nil {
-			if isModel {
-				pointedModelAsProp = prop
-				pointedModel = allModels[nextModel]
-			} else {
-				return printPrimitive(w, prop)
-			}
-		} else {
-			return fmt.Errorf("field %q does not exist", field)
-		}
-	}
-	return printModelInfo(w, pointedModel, pointedModelAsProp, recursive)
-}
-
-func splitDotNotation(model string) (string, []string) {
-	var fieldsPath []string
-	dotModel := strings.Split(model, ".")
-	if len(dotModel) >= 1 {
-		fieldsPath = dotModel[1:]
-	}
-	return dotModel[0], fieldsPath
-}
-
-func getPointedModel(prop *swagger.ModelProperty) (string, bool) {
-	if prop.Ref != nil {
-		return *prop.Ref, true
-	} else if *prop.Type == "array" && prop.Items.Ref != nil {
-		return *prop.Items.Ref, true
-	}
-	return "", false
-}
-
-func getField(model *swagger.NamedModel, sField string) (*swagger.NamedModelProperty, string, bool) {
-	for _, prop := range model.Model.Properties.List {
-		if prop.Name == sField {
-			pointedModel, isModel := getPointedModel(&prop.Property)
-			return &prop, pointedModel, isModel
-		}
-	}
-	return nil, "", false
-}
-
-func printModelInfo(w io.Writer, model *swagger.NamedModel, modelProp *swagger.NamedModelProperty, recursive bool) error {
-	t, _ := getFieldType(&modelProp.Property)
-	fmt.Fprintf(w, "RESOURCE: %s <%s>\n\n", modelProp.Name, t)
-	fieldDesc, _ := wrapAndIndentText(modelProp.Property.Description, "    ", 80)
-	fmt.Fprintf(w, "DESCRIPTION:\n%s\n\n%s\n", fieldDesc, indentText(model.Model.Description, "    "))
-	return printFields(w, model, recursive)
-}
-
-func printPrimitive(w io.Writer, field *swagger.NamedModelProperty) error {
-	t, _ := getFieldType(&field.Property)
-	fmt.Fprintf(w, "FIELD: %s <%s>\n\n", field.Name, t)
-	d, _ := wrapAndIndentText(field.Property.Description, "    ", 80)
-	fmt.Fprintf(w, "DESCRIPTION:\n%s\n", d)
-	return nil
-}
-
-func printTopLevelResourceInfo(w io.Writer, model *swagger.NamedModel, recursive bool) error {
-	fmt.Fprintf(w, "DESCRIPTION:\n%s\n", model.Model.Description)
-	return printFields(w, model, recursive)
-}
-
-func printFields(w io.Writer, model *swagger.NamedModel, recursive bool) error {
-	fmt.Fprint(w, "\nFIELDS:\n")
-	for _, field := range model.Model.Properties.List {
-		fieldType, err := getFieldType(&field.Property)
-		if err != nil {
-			return err
-		}
-
-		if arrayContains(model.Model.Required, field.Name) {
-			fmt.Fprintf(w, "   %s\t<%s> -required-\n", field.Name, fieldType)
-		} else {
-			fmt.Fprintf(w, "   %s\t<%s>\n", field.Name, fieldType)
-		}
-
-		if recursive {
-			pointedModel, isModel := getPointedModel(&field.Property)
-			if isModel {
-				for _, nestedField := range allModels[pointedModel].Model.Properties.List {
-					t, _ := getFieldType(&nestedField.Property)
-					fmt.Fprintf(w, "       %s\t<%s>\n", nestedField.Name, t)
-				}
-			}
-		} else {
-			fieldDesc, _ := wrapAndIndentText(field.Property.Description, "    ", 80)
-			fmt.Fprintf(w, "%s\n\n", fieldDesc)
-		}
-	}
-	fmt.Fprint(w, "\n")
-	return nil
-}
-
-func getFieldType(prop *swagger.ModelProperty) (string, error) {
-	if prop.Type == nil {
-		return "Object", nil
-	} else if *prop.Type == "any" {
-		// Swagger Spec doesn't return information for maps.
-		return "map[string]string", nil
-	} else if *prop.Type == "array" {
-		if prop.Items == nil {
-			return "", fmt.Errorf("error in swagger spec. Property: %v contains an array without type", prop)
-		}
-		if prop.Items.Ref != nil {
-			fieldType := "[]Object"
-			return fieldType, nil
-		}
-		fieldType := "[]" + *prop.Items.Type
-		return fieldType, nil
-	}
-	return *prop.Type, nil
-}
-
-func wrapAndIndentText(desc, indent string, lim int) (string, error) {
-	words := strings.Split(strings.Replace(strings.TrimSpace(desc), "\n", " ", -1), " ")
-	n := len(words)
-
-	for i := 0; i < n; i++ {
-		if len(words[i]) > lim {
-			if strings.Contains(words[i], "/") {
-				s := breakURL(words[i])
-				words = append(words[:i], append(s, words[i+1:]...)...)
-				i = i + len(s) - 1
-			} else {
-				fmt.Println(len(words[i]))
-				return "", fmt.Errorf("there are words longer that the break limit is")
-			}
-		}
-	}
-
-	var lines []string
-	line := []string{indent}
-	lineL := len(indent)
-	for i := 0; i < len(words); i++ {
-		w := words[i]
-
-		if strings.HasSuffix(w, "/") && lineL+len(w)-1 < lim {
-			prev := line[len(line)-1]
-			if strings.HasSuffix(prev, "/") {
-				if i+1 < len(words)-1 && !strings.HasSuffix(words[i+1], "/") {
-					w = strings.TrimSuffix(w, "/")
-				}
-
-				line[len(line)-1] = prev + w
-				lineL += len(w)
-			} else {
-				line = append(line, w)
-				lineL += len(w) + 1
-			}
-		} else if lineL+len(w) < lim {
-			line = append(line, w)
-			lineL += len(w) + 1
-		} else {
-			lines = append(lines, strings.Join(line, " "))
-			line = []string{indent, w}
-			lineL = len(indent) + len(w)
-		}
-	}
-	lines = append(lines, strings.Join(line, " "))
-
-	return strings.Join(lines, "\n"), nil
-}
-
-func breakURL(url string) []string {
-	var buf []string
-	for _, part := range strings.Split(url, "/") {
-		buf = append(buf, part+"/")
-	}
-	return buf
-}
-
-func indentText(text, indent string) string {
-	lines := strings.Split(text, "\n")
-	for i := range lines {
-		lines[i] = indent + lines[i]
-	}
-	return strings.Join(lines, "\n")
-}
-
-func arrayContains(s []string, e string) bool {
-	for _, a := range s {
-		if a == e {
-			return true
-		}
-	}
-	return false
-}

pkg/kubectl/explain/BUILD

@@ -0,0 +1,34 @@
+load("@io_bazel_rules_go//go:def.bzl", "go_library")
+
+go_library(
+    name = "go_default_library",
+    srcs = [
+        "explain.go",
+        "field_lookup.go",
+        "fields_printer.go",
+        "fields_printer_builder.go",
+        "formatter.go",
+        "model_printer.go",
+        "recursive_fields_printer.go",
+        "typename.go",
+    ],
+    visibility = ["//visibility:public"],
+    deps = [
+        "//pkg/kubectl/cmd/util/openapi:go_default_library",
+        "//vendor/k8s.io/apimachinery/pkg/api/meta:go_default_library",
+    ],
+)
+
+filegroup(
+    name = "package-srcs",
+    srcs = glob(["**"]),
+    tags = ["automanaged"],
+    visibility = ["//visibility:private"],
+)
+
+filegroup(
+    name = "all-srcs",
+    srcs = [":package-srcs"],
+    tags = ["automanaged"],
+    visibility = ["//visibility:public"],
+)

pkg/kubectl/explain/explain.go

@@ -0,0 +1,64 @@
+/*
+Copyright 2017 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package explain
+
+import (
+	"io"
+	"strings"
+
+	"k8s.io/apimachinery/pkg/api/meta"
+	"k8s.io/kubernetes/pkg/kubectl/cmd/util/openapi"
+)
+
+type fieldsPrinter interface {
+	PrintFields(openapi.Schema) error
+}
+
+func splitDotNotation(model string) (string, []string) {
+	var fieldsPath []string
+	dotModel := strings.Split(model, ".")
+	if len(dotModel) >= 1 {
+		fieldsPath = dotModel[1:]
+	}
+	return dotModel[0], fieldsPath
+}
+
+// SplitAndParseResourceRequest separates the users input into a model and fields
+func SplitAndParseResourceRequest(inResource string, mapper meta.RESTMapper) (string, []string, error) {
+	inResource, fieldsPath := splitDotNotation(inResource)
+	inResource, _ = mapper.ResourceSingularizer(inResource)
+	return inResource, fieldsPath, nil
+}
+
+// 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 openapi.Schema, recursive bool) error {
+	fieldName := ""
+	if len(fieldsPath) != 0 {
+		fieldName = fieldsPath[len(fieldsPath)-1]
+	}
+
+	// Go down the fieldsPath to find what we're trying to explain
+	schema, err := LookupSchemaForField(schema, fieldsPath)
+	if err != nil {
+		return err
+	}
+	b := fieldsPrinterBuilder{Recursive: recursive}
+	f := &Formatter{Writer: w, Wrap: 80}
+	return PrintModel(fieldName, f, b, schema)
+}

pkg/kubectl/explain/field_lookup.go

@@ -0,0 +1,107 @@
+/*
+Copyright 2017 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package explain
+
+import (
+	"fmt"
+
+	"k8s.io/kubernetes/pkg/kubectl/cmd/util/openapi"
+)
+
+// fieldLookup walks through a schema by following a path, and returns
+// the final schema.
+type fieldLookup struct {
+	// Path to walk
+	Path []string
+
+	// Return information: Schema found, or error.
+	Schema openapi.Schema
+	Error  error
+}
+
+// SaveLeafSchema is used to detect if we are done walking the path, and
+// saves the schema as a match.
+func (f *fieldLookup) SaveLeafSchema(schema openapi.Schema) bool {
+	if len(f.Path) != 0 {
+		return false
+	}
+
+	f.Schema = schema
+
+	return true
+}
+
+// VisitArray is mostly a passthrough.
+func (f *fieldLookup) VisitArray(a *openapi.Array) {
+	if f.SaveLeafSchema(a) {
+		return
+	}
+
+	// Passthrough arrays.
+	a.SubType.Accept(f)
+}
+
+// VisitMap is mostly a passthrough.
+func (f *fieldLookup) VisitMap(m *openapi.Map) {
+	if f.SaveLeafSchema(m) {
+		return
+	}
+
+	// Passthrough maps.
+	m.SubType.Accept(f)
+}
+
+// VisitPrimitive stops the operation and returns itself as the found
+// schema, even if it had more path to walk.
+func (f *fieldLookup) VisitPrimitive(p *openapi.Primitive) {
+	// Even if Path is not empty (we're not expecting a leaf),
+	// return that primitive.
+	f.Schema = p
+}
+
+// VisitKind unstacks fields as it finds them.
+func (f *fieldLookup) VisitKind(k *openapi.Kind) {
+	if f.SaveLeafSchema(k) {
+		return
+	}
+
+	subSchema, ok := k.Fields[f.Path[0]]
+	if !ok {
+		f.Error = fmt.Errorf("field %q does not exist", f.Path[0])
+		return
+	}
+
+	f.Path = f.Path[1:]
+	subSchema.Accept(f)
+}
+
+// VisitReference is mostly a passthrough.
+func (f *fieldLookup) VisitReference(r openapi.Reference) {
+	if f.SaveLeafSchema(r) {
+		return
+	}
+
+	// Passthrough references.
+	r.SubSchema().Accept(f)
+}
+
+// LookupSchemaForField looks for the schema of a given path in a base schema.
+func LookupSchemaForField(schema openapi.Schema, path []string) (openapi.Schema, error) {
+	f := &fieldLookup{Path: path}
+	schema.Accept(f)
+	return f.Schema, f.Error
+}

pkg/kubectl/explain/fields_printer.go

@@ -0,0 +1,84 @@
+/*
+Copyright 2017 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package explain
+
+import (
+	"k8s.io/kubernetes/pkg/kubectl/cmd/util/openapi"
+)
+
+// indentDesc is the level of indentation for descriptions.
+const indentDesc = 2
+
+// regularFieldsPrinter prints fields with their type and description.
+type regularFieldsPrinter struct {
+	Writer *Formatter
+	Error  error
+}
+
+var _ openapi.SchemaVisitor = &regularFieldsPrinter{}
+var _ fieldsPrinter = &regularFieldsPrinter{}
+
+// VisitArray prints a Array type. It is just a passthrough.
+func (f *regularFieldsPrinter) VisitArray(a *openapi.Array) {
+	a.SubType.Accept(f)
+}
+
+// VisitKind prints a Kind type. It prints each key in the kind, with
+// the type, the required flag, and the description.
+func (f *regularFieldsPrinter) VisitKind(k *openapi.Kind) {
+	for _, key := range k.Keys() {
+		v := k.Fields[key]
+		required := ""
+		if k.IsRequired(key) {
+			required = " -required-"
+		}
+
+		if err := f.Writer.Write("%s\t<%s>%s", key, GetTypeName(v), required); err != nil {
+			f.Error = err
+			return
+		}
+		if err := f.Writer.Indent(indentDesc).WriteWrapped("%s", v.GetDescription()); err != nil {
+			f.Error = err
+			return
+		}
+		if err := f.Writer.Write(""); err != nil {
+			f.Error = err
+			return
+		}
+	}
+}
+
+// VisitMap prints a Map type. It is just a passthrough.
+func (f *regularFieldsPrinter) VisitMap(m *openapi.Map) {
+	m.SubType.Accept(f)
+}
+
+// VisitPrimitive prints a Primitive type. It stops the recursion.
+func (f *regularFieldsPrinter) VisitPrimitive(p *openapi.Primitive) {
+	// Nothing to do. Shouldn't really happen.
+}
+
+// VisitReference prints a Reference type. It is just a passthrough.
+func (f *regularFieldsPrinter) VisitReference(r openapi.Reference) {
+	r.SubSchema().Accept(f)
+}
+
+// PrintFields will write the types from schema.
+func (f *regularFieldsPrinter) PrintFields(schema openapi.Schema) error {
+	schema.Accept(f)
+	return f.Error
+}

pkg/kubectl/explain/fields_printer_builder.go

@@ -0,0 +1,36 @@
+/*
+Copyright 2017 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package explain
+
+// fieldsPrinterBuilder builds either a regularFieldsPrinter or a
+// recursiveFieldsPrinter based on the argument.
+type fieldsPrinterBuilder struct {
+	Recursive bool
+}
+
+// BuildFieldsPrinter builds the appropriate fieldsPrinter.
+func (f fieldsPrinterBuilder) BuildFieldsPrinter(writer *Formatter) fieldsPrinter {
+	if f.Recursive {
+		return &recursiveFieldsPrinter{
+			Writer: writer,
+		}
+	}
+
+	return &regularFieldsPrinter{
+		Writer: writer,
+	}
+}

pkg/kubectl/explain/formatter.go

@@ -0,0 +1,120 @@
+/*
+Copyright 2017 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package explain
+
+import (
+	"fmt"
+	"io"
+	"strings"
+)
+
+// Formatter helps you write with indentation, and can wrap text as needed.
+type Formatter struct {
+	IndentLevel int
+	Wrap        int
+	Writer      io.Writer
+}
+
+// Indent creates a new Formatter that will indent the code by that much more.
+func (f Formatter) Indent(indent int) *Formatter {
+	f.IndentLevel = f.IndentLevel + indent
+	return &f
+}
+
+// Write writes a string with the indentation set for the
+// Formatter. This is not wrapping text.
+func (f *Formatter) Write(str string, a ...interface{}) error {
+	// Don't indent empty lines
+	if str == "" {
+		_, err := io.WriteString(f.Writer, "\n")
+		return err
+	}
+
+	indent := ""
+	for i := 0; i < f.IndentLevel; i++ {
+		indent = indent + " "
+	}
+	_, err := io.WriteString(f.Writer, indent+fmt.Sprintf(str, a...)+"\n")
+	return err
+}
+
+// WriteWrapped writes a string with the indentation set for the
+// Formatter, and wraps as needed.
+func (f *Formatter) WriteWrapped(str string, a ...interface{}) error {
+	if f.Wrap == 0 {
+		return f.Write(str, a...)
+	}
+	text := fmt.Sprintf(str, a...)
+	strs := wrapString(text, f.Wrap-f.IndentLevel)
+	for _, substr := range strs {
+		if err := f.Write(substr); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+type line struct {
+	wrap  int
+	words []string
+}
+
+func (l *line) String() string {
+	return strings.Join(l.words, " ")
+}
+
+func (l *line) Empty() bool {
+	return len(l.words) == 0
+}
+
+func (l *line) Len() int {
+	return len(l.String())
+}
+
+// Add adds the word to the line, returns true if we could, false if we
+// didn't have enough room. It's always possible to add to an empty line.
+func (l *line) Add(word string) bool {
+	newLine := line{
+		wrap:  l.wrap,
+		words: append(l.words, word),
+	}
+	if newLine.Len() <= l.wrap || len(l.words) == 0 {
+		l.words = newLine.words
+		return true
+	}
+	return false
+}
+
+func wrapString(str string, wrap int) []string {
+	words := strings.Fields(str)
+	wrapped := []string{}
+	l := line{wrap: wrap}
+
+	for _, word := range words {
+		if l.Add(word) == false {
+			wrapped = append(wrapped, l.String())
+			l = line{wrap: wrap}
+			if l.Add(word) == false {
+				panic("Couldn't add to empty line.")
+			}
+		}
+	}
+	if !l.Empty() {
+		wrapped = append(wrapped, l.String())
+	}
+	return wrapped
+}

pkg/kubectl/explain/model_printer.go

@@ -0,0 +1,129 @@
+/*
+Copyright 2017 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package explain
+
+import (
+	"k8s.io/kubernetes/pkg/kubectl/cmd/util/openapi"
+)
+
+// fieldIndentLevel is the level of indentation for fields.
+const fieldIndentLevel = 3
+
+// descriptionIndentLevel is the level of indentation for the
+// description.
+const descriptionIndentLevel = 5
+
+// modelPrinter prints a schema in Writer. Its "Builder" will decide if
+// it's recursive or not.
+type modelPrinter struct {
+	Name         string
+	Type         string
+	Descriptions []string
+	Writer       *Formatter
+	Builder      fieldsPrinterBuilder
+	Error        error
+}
+
+var _ openapi.SchemaVisitor = &modelPrinter{}
+
+// 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.
+func (m *modelPrinter) PrintDescription(schema openapi.Schema) error {
+	if err := m.Writer.Write("DESCRIPTION:"); err != nil {
+		return err
+	}
+	for i, desc := range append(m.Descriptions, schema.GetDescription()) {
+		if desc == "" {
+			continue
+		}
+		if i != 0 {
+			if err := m.Writer.Write(""); err != nil {
+				return err
+			}
+		}
+		if err := m.Writer.Indent(descriptionIndentLevel).WriteWrapped(desc); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+// VisitArray recurses inside the subtype, while collecting the type if
+// not done yet, and the description.
+func (m *modelPrinter) VisitArray(a *openapi.Array) {
+	m.Descriptions = append(m.Descriptions, a.GetDescription())
+	if m.Type == "" {
+		m.Type = GetTypeName(a)
+	}
+	a.SubType.Accept(m)
+}
+
+// VisitKind prints a full resource with its fields.
+func (m *modelPrinter) VisitKind(k *openapi.Kind) {
+	if m.Type == "" {
+		m.Type = GetTypeName(k)
+	}
+	if m.Name != "" {
+		m.Writer.Write("RESOURCE: %s <%s>\n", m.Name, m.Type)
+	}
+
+	if err := m.PrintDescription(k); err != nil {
+		m.Error = err
+		return
+	}
+	if err := m.Writer.Write("\nFIELDS:"); err != nil {
+		m.Error = err
+		return
+	}
+	m.Error = m.Builder.BuildFieldsPrinter(m.Writer.Indent(fieldIndentLevel)).PrintFields(k)
+}
+
+// VisitMap recurses inside the subtype, while collecting the type if
+// not done yet, and the description.
+func (m *modelPrinter) VisitMap(om *openapi.Map) {
+	m.Descriptions = append(m.Descriptions, om.GetDescription())
+	if m.Type == "" {
+		m.Type = GetTypeName(om)
+	}
+	om.SubType.Accept(m)
+}
+
+// VisitPrimitive prints a field type and its description.
+func (m *modelPrinter) VisitPrimitive(p *openapi.Primitive) {
+	if m.Type == "" {
+		m.Type = GetTypeName(p)
+	}
+	if err := m.Writer.Write("FIELD: %s <%s>\n", m.Name, m.Type); err != nil {
+		m.Error = err
+		return
+	}
+	m.Error = m.PrintDescription(p)
+}
+
+// VisitReference recurses inside the subtype, while collecting the description.
+func (m *modelPrinter) VisitReference(r openapi.Reference) {
+	m.Descriptions = append(m.Descriptions, r.GetDescription())
+	r.SubSchema().Accept(m)
+}
+
+// PrintModel prints the description of a schema in writer.
+func PrintModel(name string, writer *Formatter, builder fieldsPrinterBuilder, schema openapi.Schema) error {
+	m := &modelPrinter{Name: name, Writer: writer, Builder: builder}
+	schema.Accept(m)
+	return m.Error
+}

pkg/kubectl/explain/recursive_fields_printer.go

@@ -0,0 +1,77 @@
+/*
+Copyright 2017 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package explain
+
+import (
+	"k8s.io/kubernetes/pkg/kubectl/cmd/util/openapi"
+)
+
+// indentPerLevel is the level of indentation for each field recursion.
+const indentPerLevel = 3
+
+// recursiveFieldsPrinter recursively prints all the fields for a given
+// schema.
+type recursiveFieldsPrinter struct {
+	Writer *Formatter
+	Error  error
+}
+
+var _ openapi.SchemaVisitor = &recursiveFieldsPrinter{}
+var _ fieldsPrinter = &recursiveFieldsPrinter{}
+
+// VisitArray is just a passthrough.
+func (f *recursiveFieldsPrinter) VisitArray(a *openapi.Array) {
+	a.SubType.Accept(f)
+}
+
+// VisitKind prints all its fields with their type, and then recurses
+// inside each of these (pre-order).
+func (f *recursiveFieldsPrinter) VisitKind(k *openapi.Kind) {
+	for _, key := range k.Keys() {
+		v := k.Fields[key]
+		f.Writer.Write("%s\t<%s>", key, GetTypeName(v))
+		subFields := &recursiveFieldsPrinter{
+			Writer: f.Writer.Indent(indentPerLevel),
+		}
+		if err := subFields.PrintFields(v); err != nil {
+			f.Error = err
+			return
+		}
+	}
+}
+
+// VisitMap is just a passthrough.
+func (f *recursiveFieldsPrinter) VisitMap(m *openapi.Map) {
+	m.SubType.Accept(f)
+}
+
+// VisitPrimitive does nothing, since it doesn't have sub-fields.
+func (f *recursiveFieldsPrinter) VisitPrimitive(p *openapi.Primitive) {
+	// Nothing to do.
+}
+
+// VisitReference is just a passthrough.
+func (f *recursiveFieldsPrinter) VisitReference(r openapi.Reference) {
+	r.SubSchema().Accept(f)
+}
+
+// PrintFields will recursively print all the fields for the given
+// schema.
+func (f *recursiveFieldsPrinter) PrintFields(schema openapi.Schema) error {
+	schema.Accept(f)
+	return f.Error
+}

pkg/kubectl/explain/typename.go

@@ -0,0 +1,66 @@
+/*
+Copyright 2017 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package explain
+
+import (
+	"fmt"
+
+	"k8s.io/kubernetes/pkg/kubectl/cmd/util/openapi"
+)
+
+// typeName finds the name of a schema
+type typeName struct {
+	Name string
+}
+
+var _ openapi.SchemaVisitor = &typeName{}
+
+// VisitArray adds the [] prefix and recurses.
+func (t *typeName) VisitArray(a *openapi.Array) {
+	s := &typeName{}
+	a.SubType.Accept(s)
+	t.Name = fmt.Sprintf("[]%s", s.Name)
+}
+
+// VisitKind just returns "Object".
+func (t *typeName) VisitKind(k *openapi.Kind) {
+	t.Name = "Object"
+}
+
+// VisitMap adds the map[string] prefix and recurses.
+func (t *typeName) VisitMap(m *openapi.Map) {
+	s := &typeName{}
+	m.SubType.Accept(s)
+	t.Name = fmt.Sprintf("map[string]%s", s.Name)
+}
+
+// VisitPrimitive returns the name of the primitive.
+func (t *typeName) VisitPrimitive(p *openapi.Primitive) {
+	t.Name = p.Type
+}
+
+// VisitReference is just a passthrough.
+func (t *typeName) VisitReference(r openapi.Reference) {
+	r.SubSchema().Accept(t)
+}
+
+// GetTypeName returns the type of a schema.
+func GetTypeName(schema openapi.Schema) string {
+	t := &typeName{}
+	schema.Accept(t)
+	return t.Name
+}