✨ Add support for +default markers

https://github.com/kubernetes/enhancements/tree/master/keps/sig-api-machinery/1929-built-in-default#summary

https://github.com/kubernetes-sigs/kubebuilder/issues/3896

Author: liggitt

pkg/crd/markers/validation.go

@@ -91,6 +91,8 @@ var FieldOnlyMarkers = []*definitionWithHelp{
 
 	must(markers.MakeAnyTypeDefinition("kubebuilder:default", markers.DescribesField, Default{})).
 		WithHelp(Default{}.Help()),
+	must(markers.MakeAnyTypeJSONDefinition("default", markers.DescribesField, KubernetesDefault{})).
+		WithHelp(KubernetesDefault{}.Help()),
 
 	must(markers.MakeAnyTypeDefinition("kubebuilder:example", markers.DescribesField, Example{})).
 		WithHelp(Example{}.Help()),
@@ -239,6 +241,19 @@ type Default struct {
 	Value interface{}
 }
 
+// +controllertools:marker:generateHelp:category="CRD validation"
+// Default sets the default value for this field.
+//
+// A default value will be accepted as any value valid for the
+// field. Formatting for common types include: boolean: `true`, string:
+// `"Cluster"`, numerical: `1.24`, array: `[1,2]`, object: `{"policy":
+// "delete"}`). Defaults should be defined in pruned form, and only best-effort
+// validation will be performed. Full validation of a default requires
+// submission of the containing CRD to an apiserver.
+type KubernetesDefault struct {
+	Value interface{}
+}
+
 // +controllertools:marker:generateHelp:category="CRD validation"
 // Example sets the example value for this field.
 //
@@ -503,6 +518,26 @@ func (m Default) ApplyToSchema(schema *apiext.JSONSchemaProps) error {
 	return nil
 }
 
+func (m Default) ApplyPriority() ApplyPriority {
+	// explicitly go after +default markers, so kubebuilder-specific defaults get applied last and stomp
+	return 10
+}
+
+// Defaults are only valid CRDs created with the v1 API
+func (m KubernetesDefault) ApplyToSchema(schema *apiext.JSONSchemaProps) error {
+	marshalledDefault, err := json.Marshal(m.Value)
+	if err != nil {
+		return err
+	}
+	schema.Default = &apiext.JSON{Raw: marshalledDefault}
+	return nil
+}
+
+func (m KubernetesDefault) ApplyPriority() ApplyPriority {
+	// explicitly go before +kubebuilder:default markers, so kubebuilder-specific defaults get applied last and stomp
+	return 9
+}
+
 func (m Example) ApplyToSchema(schema *apiext.JSONSchemaProps) error {
 	marshalledExample, err := json.Marshal(m.Value)
 	if err != nil {

pkg/crd/markers/zz_generated.markerhelp.go

@@ -133,6 +133,35 @@ type CronJobSpec struct {
 	// +kubebuilder:default={}
 	DefaultedEmptyObject EmpiableObject `json:"defaultedEmptyObject"`
 
+	// This tests that kubebuilder defaulting takes precedence.
+	// +kubebuilder:default="kubebuilder-default"
+	// +default="kubernetes-default"
+	DoubleDefaultedString string `json:"doubleDefaultedString"`
+
+	// This tests that primitive defaulting can be performed.
+	// +default="forty-two"
+	KubernetesDefaultedString string `json:"kubernetesDefaultedString"`
+
+	// This tests that slice defaulting can be performed.
+	// +default=["a","b"]
+	KubernetesDefaultedSlice []string `json:"kubernetesDefaultedSlice"`
+
+	// This tests that object defaulting can be performed.
+	// +default=[{"nested": {"foo": "baz", "bar": true}},{"nested": {"bar": false}}]
+	KubernetesDefaultedObject []RootObject `json:"kubernetesDefaultedObject"`
+
+	// This tests that empty slice defaulting can be performed.
+	// +default=[]
+	KubernetesDefaultedEmptySlice []string `json:"kubernetesDefaultedEmptySlice"`
+
+	// This tests that an empty object defaulting can be performed on a map.
+	// +default={}
+	KubernetesDefaultedEmptyMap map[string]string `json:"kubernetesDefaultedEmptyMap"`
+
+	// This tests that an empty object defaulting can be performed on an object.
+	// +default={}
+	KubernetesDefaultedEmptyObject EmpiableObject `json:"kubernetesDefaultedEmptyObject"`
+
 	// This tests that pattern validator is properly applied.
 	// +kubebuilder:validation:Pattern=`^$|^((https):\/\/?)[^\s()<>]+(?:\([\w\d]+\)|([^[:punct:]\s]|\/?))$`
 	PatternObject string `json:"patternObject"`

pkg/crd/testdata/cronjob_types.go

@@ -172,6 +172,70 @@ spec:
                 description: This tests that primitive defaulting can be performed.
                 example: forty-two
                 type: string
+              doubleDefaultedString:
+                default: kubebuilder-default
+                description: This tests that kubebuilder defaulting takes precedence.
+                type: string
+              kubernetesDefaultedEmptyMap:
+                additionalProperties:
+                  type: string
+                default: {}
+                description: This tests that an empty object defaulting can be performed
+                  on a map.
+                type: object
+              kubernetesDefaultedEmptyObject:
+                default: {}
+                description: This tests that an empty object defaulting can be performed
+                  on an object.
+                properties:
+                  bar:
+                    type: string
+                  foo:
+                    default: forty-two
+                    type: string
+                type: object
+              kubernetesDefaultedEmptySlice:
+                default: []
+                description: This tests that empty slice defaulting can be performed.
+                items:
+                  type: string
+                type: array
+              kubernetesDefaultedObject:
+                default:
+                - nested:
+                    bar: true
+                    foo: baz
+                - nested:
+                    bar: false
+                description: This tests that object defaulting can be performed.
+                items:
+                  properties:
+                    nested:
+                      properties:
+                        bar:
+                          type: boolean
+                        foo:
+                          type: string
+                      required:
+                      - bar
+                      - foo
+                      type: object
+                  required:
+                  - nested
+                  type: object
+                type: array
+              kubernetesDefaultedSlice:
+                default:
+                - a
+                - b
+                description: This tests that slice defaulting can be performed.
+                items:
+                  type: string
+                type: array
+              kubernetesDefaultedString:
+                default: forty-two
+                description: This tests that primitive defaulting can be performed.
+                type: string
               embeddedResource:
                 type: object
                 x-kubernetes-embedded-resource: true
@@ -6886,13 +6950,20 @@ spec:
             - defaultedObject
             - defaultedSlice
             - defaultedString
+            - doubleDefaultedString
             - embeddedResource
             - float64WithValidations
             - floatWithValidations
             - foo
             - int32WithValidations
             - intWithValidations
             - jobTemplate
+            - kubernetesDefaultedEmptyMap
+            - kubernetesDefaultedEmptyObject
+            - kubernetesDefaultedEmptySlice
+            - kubernetesDefaultedObject
+            - kubernetesDefaultedSlice
+            - kubernetesDefaultedString
             - mapOfInfo
             - nestedMapOfInfo
             - nestedStructWithSeveralFields

pkg/crd/testdata/testdata.kubebuilder.io_cronjobs.yaml

@@ -18,6 +18,8 @@ package markers
 
 import (
 	"bytes"
+	"encoding/json"
+	"errors"
 	"fmt"
 	"reflect"
 	"strconv"
@@ -726,6 +728,11 @@ type Definition struct {
 	// Strict indicates that this definition should error out when parsing if
 	// not all non-optional fields were seen.
 	Strict bool
+
+	// parseJSON indicates the value should be parsed using json parsing.
+	// This means strings must be quoted, arrays must use [] notation, etc.
+	// This is only allowed when AnonymousField() is true.
+	parseJSON bool
 }
 
 // AnonymousField indicates that the definition has one field,
@@ -824,6 +831,47 @@ func parserScanner(raw string, err func(*sc.Scanner, string)) *sc.Scanner {
 // raw marker in the form `+a:b:c=arg,d=arg` into an output object of the
 // type specified in the definition.
 func (d *Definition) Parse(rawMarker string) (interface{}, error) {
+	if d.parseJSON {
+		return d.parseWithJSON(rawMarker)
+	} else {
+		return d.parseWithScanner(rawMarker)
+	}
+}
+
+func (d *Definition) parseWithJSON(rawMarker string) (interface{}, error) {
+	_, _, fields := splitMarker(rawMarker)
+
+	out := reflect.Indirect(reflect.New(d.Output))
+
+	var errs []error
+	if !d.AnonymousField() {
+		errs = append(errs, errors.New("parseJSON requires anonymous definition"))
+		return out.Interface(), loader.MaybeErrList(errs)
+	}
+
+	// might still be a struct that something fiddled with, so double check
+	structFieldName := d.FieldNames[""]
+	outTarget := out
+	if structFieldName != "" {
+		// it's a struct field mapped to an anonymous marker
+		outTarget = out.FieldByName(structFieldName)
+		if !outTarget.CanSet() {
+			errs = append(errs, fmt.Errorf("cannot set field %q (might not exist)", structFieldName))
+			return out.Interface(), loader.MaybeErrList(errs)
+		}
+	}
+
+	var i any
+	if err := json.Unmarshal([]byte(fields), &i); err != nil {
+		errs = append(errs, err)
+	} else {
+		castAndSet(outTarget, reflect.ValueOf(i))
+	}
+
+	return out.Interface(), loader.MaybeErrList(errs)
+}
+
+func (d *Definition) parseWithScanner(rawMarker string) (interface{}, error) {
 	name, anonName, fields := splitMarker(rawMarker)
 
 	out := reflect.Indirect(reflect.New(d.Output))
@@ -952,6 +1000,18 @@ func MakeAnyTypeDefinition(name string, target TargetType, output interface{}) (
 	return defn, nil
 }
 
+// MakeAnyTypeJSONDefinition constructs a definition for an output struct with a
+// field named `Value` of type `interface{}`. The argument to the marker will
+// be parsed as AnyType using json parsing and assigned to the field named `Value`.
+func MakeAnyTypeJSONDefinition(name string, target TargetType, output interface{}) (*Definition, error) {
+	defn, err := MakeAnyTypeDefinition(name, target, output)
+	if err != nil {
+		return nil, err
+	}
+	defn.parseJSON = true
+	return defn, nil
+}
+
 // splitMarker takes a marker in the form of `+a:b:c=arg,d=arg` and splits it
 // into the name (`a:b`), the name if it's not a struct (`a:b:c`), and the parts
 // that are definitely fields (`arg,d=arg`).