Object scaffolding logic from KubeBuilder

This extracts KubeBuilder's object scaffolding logic into a separate
command.  Creating the basic structure for Kubernetes objects is a
non-opinionated task, so it can be reused for other purposes
(incrementally adding types to files, non-KubeBuilder scaffolding
projects, etc).

cmd/type-scaffold/main.go

@@ -0,0 +1,72 @@
+/*
+Copyright 2018 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 main
+
+import (
+	"fmt"
+	"os"
+
+	"github.com/spf13/cobra"
+	"sigs.k8s.io/controller-tools/pkg/typescaffold"
+)
+
+func main() {
+	opts := &typescaffold.ScaffoldOptions{
+		Resource: typescaffold.Resource{
+			Namespaced: true,
+		},
+	}
+	scaffoldCmd := &cobra.Command{
+		Use:   "type-scaffold",
+		Short: "Quickly scaffold out basic bits of a Kubernetes type.",
+		Long: `Quickly scaffold out the structure of a type for a Kubernetes kind and associated types.
+Produces:
+
+- a root type with approparite metadata fields
+- Spec and Status types
+- a list type
+
+Also applies the appropriate comments to generate the code required to conform to runtime.Object.`,
+		Example: `	# Generate types for a Kind called Foo with a resource called foos
+		type-scaffold --kind Foo
+
+	# Generate types for a Kind called Bar with a resource of foobars
+	type-scaffold --kind Bar --resource foobars`,
+		RunE: func(cmd *cobra.Command, args []string) error {
+			if err := opts.Validate(); err != nil {
+				return err
+			}
+
+			return opts.Scaffold(os.Stdout)
+		},
+	}
+
+	scaffoldCmd.Flags().StringVar(&opts.Resource.Kind, "kind", opts.Resource.Kind, "The kind of the typescaffold being scaffolded.")
+	scaffoldCmd.Flags().StringVar(&opts.Resource.Resource, "resource", opts.Resource.Resource, "The resource of the typescaffold being scaffolded (defaults to a lower-case, plural version of kind).")
+	scaffoldCmd.Flags().BoolVar(&opts.Resource.Namespaced, "namespaced", opts.Resource.Namespaced, "Whether or not the given resource is namespaced.")
+
+	if err := cobra.MarkFlagRequired(scaffoldCmd.Flags(), "kind"); err != nil {
+		panic("unable to mark --kind as required")
+	}
+
+	if err := scaffoldCmd.Execute(); err != nil {
+		if _, err := fmt.Fprintln(os.Stderr, err); err != nil {
+			// this would be exceedingly bizarre if we ever got here
+			panic("unable to write to error details to standard error")
+		}
+		os.Exit(1)
+	}
+}

pkg/typescaffold/resource.go

@@ -0,0 +1,54 @@
+/*
+Copyright 2018 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 typescaffold
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/markbates/inflect"
+)
+
+// Resource contains the information required to scaffold files for a resource.
+type Resource struct {
+	// Namespaced is true if the resource is namespaced
+	Namespaced bool
+
+	// Kind is the API Kind.
+	Kind string
+
+	// Resource is the API Resource.
+	Resource string
+}
+
+// Validate checks the Resource values to make sure they are valid.
+func (r *Resource) Validate() error {
+	if len(r.Kind) == 0 {
+		return fmt.Errorf("kind cannot be empty")
+	}
+
+	rs := inflect.NewDefaultRuleset()
+	if len(r.Resource) == 0 {
+		r.Resource = rs.Pluralize(strings.ToLower(r.Kind))
+	}
+
+	if r.Kind != inflect.Camelize(r.Kind) {
+		return fmt.Errorf("Kind must be camelcase (expected %s was %s)", inflect.Camelize(r.Kind), r.Kind)
+	}
+
+	return nil
+}

pkg/typescaffold/scaffold.go

@@ -0,0 +1,105 @@
+/*
+Copyright 2018 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 typescaffold
+
+import (
+	"io"
+	"strings"
+	"text/template"
+)
+
+var (
+	typesTemplateRaw = `// {{.Resource.Kind}}Spec defines the desired state of {{.Resource.Kind}}
+type {{.Resource.Kind}}Spec struct {
+	// INSERT ADDITIONAL SPEC FIELDS -- desired state of cluster
+{{- if .AdditionalHelp }}
+{{- range .AdditionalHelp | SplitLines }}
+	// {{.}}
+{{- end }}
+{{- end }}
+}
+
+// {{.Resource.Kind}}Status defines the observed state of {{.Resource.Kind}}.
+// It should always be reconstructable from the state of the cluster and/or outside world.
+type {{.Resource.Kind}}Status struct {
+	// INSERT ADDITIONAL STATUS FIELDS -- observed state of cluster
+{{- if .AdditionalHelp }}
+{{- range .AdditionalHelp | SplitLines }}
+	// {{.}}
+{{- end }}
+{{- end }}
+}
+
+// +k8s:deepcopy-gen:interfaces=k8s.io/apimachinery/pkg/runtime.Object
+{{- if .GenerateClients }}
+// +genclient
+{{- if not .Resource.Namespaced }}
+// +genclient:nonNamespaced
+{{- end }}
+{{- end }}
+
+// {{.Resource.Kind}} is the Schema for the {{ .Resource.Resource }} API
+// +k8s:openapi-gen=true
+type {{.Resource.Kind}} struct {
+	metav1.TypeMeta   ` + "`" + `json:",inline"` + "`" + `
+	metav1.ObjectMeta ` + "`" + `json:"metadata,omitempty"` + "`" + `
+
+	Spec   {{.Resource.Kind}}Spec   ` + "`" + `json:"spec,omitempty"` + "`" + `
+	Status {{.Resource.Kind}}Status ` + "`" + `json:"status,omitempty"` + "`" + `
+}
+
+// +k8s:deepcopy-gen:interfaces=k8s.io/apimachinery/pkg/runtime.Object
+{{- if and (.GenerateClients) (not .Resource.Namespaced) }}
+// +genclient:nonNamespaced
+{{- end }}
+
+// {{.Resource.Kind}}List contains a list of {{.Resource.Kind}}
+type {{.Resource.Kind}}List struct {
+	metav1.TypeMeta ` + "`" + `json:",inline"` + "`" + `
+	metav1.ListMeta ` + "`" + `json:"metadata,omitempty"` + "`" + `
+	Items           []{{ .Resource.Kind }} ` + "`" + `json:"items"` + "`" + `
+}
+`
+	typesTemplateHelpers = template.FuncMap{
+		"SplitLines": func(raw string) []string { return strings.Split(raw, "\n") },
+	}
+
+	typesTemplate = template.Must(template.New("object-scaffolding").Funcs(typesTemplateHelpers).Parse(typesTemplateRaw))
+)
+
+// ScaffoldOptions describes how to scaffold out a Kubernetes object
+// with the basic metadata and comment annotations required to generate code
+// for and conform to runtime.Object and metav1.Object.
+type ScaffoldOptions struct {
+	Resource        Resource
+	AdditionalHelp  string
+	GenerateClients bool
+}
+
+// Validate validates the options, returning an error if anything is invalid.
+func (o *ScaffoldOptions) Validate() error {
+	if err := o.Resource.Validate(); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+// Scaffold prints the Kubernetes object scaffolding to the given output.
+func (o *ScaffoldOptions) Scaffold(out io.Writer) error {
+	return typesTemplate.Execute(out, o)
+}

pkg/typescaffold/scaffold_test.go

@@ -0,0 +1,104 @@
+/*
+Copyright 2018 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 typescaffold_test
+
+import (
+	"bytes"
+	"testing"
+
+	"sigs.k8s.io/controller-tools/pkg/typescaffold"
+)
+
+func TestScaffold(t *testing.T) {
+	tests := []struct {
+		name string
+		opts typescaffold.ScaffoldOptions
+	}{
+		{
+			name: "kind only",
+			opts: typescaffold.ScaffoldOptions{
+				Resource: typescaffold.Resource{
+					Kind: "Foo",
+				},
+			},
+		},
+		{
+			name: "kind and resource",
+			opts: typescaffold.ScaffoldOptions{
+				Resource: typescaffold.Resource{
+					Kind:     "Foo",
+					Resource: "foos",
+				},
+			},
+		},
+		{
+			name: "namespaced",
+			opts: typescaffold.ScaffoldOptions{
+				Resource: typescaffold.Resource{
+					Kind:       "Foo",
+					Resource:   "foos",
+					Namespaced: true,
+				},
+			},
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			err := test.opts.Validate()
+			if err != nil {
+				t.Fatalf("unable to validate scaffold opts: %v", err)
+			}
+			var out bytes.Buffer
+			if err := test.opts.Scaffold(&out); err != nil {
+				t.Fatalf("unable to scaffold types: %v", err)
+			}
+
+			// TODO(directxman12): testing the direct output seems fragile
+			// there must be a better way.
+		})
+	}
+}
+
+func TestInvalidScaffoldOpts(t *testing.T) {
+	tests := []struct {
+		name string
+		opts typescaffold.ScaffoldOptions
+	}{
+		{
+			name: "bad kind",
+			opts: typescaffold.ScaffoldOptions{
+				Resource: typescaffold.Resource{
+					Kind: "Foo_bats",
+				},
+			},
+		},
+		{
+			name: "no kind",
+			opts: typescaffold.ScaffoldOptions{},
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			err := test.opts.Validate()
+			if err == nil {
+				t.Fatalf("expected error -- those options were invalid")
+			}
+		})
+	}
+}