Handle optional value-types with defaults

staging/src/k8s.io/code-generator/cmd/validation-gen/output_tests/tags/optional/nonzero_defaults/doc.go

@@ -0,0 +1,53 @@
+/*
+Copyright 2025 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.
+*/
+
+// +k8s:validation-gen=TypeMeta
+// +k8s:validation-gen-scheme-registry=k8s.io/code-generator/cmd/validation-gen/testscheme.Scheme
+
+// This is a test package.
+package nonzerodefaults
+
+import "k8s.io/code-generator/cmd/validation-gen/testscheme"
+
+var localSchemeBuilder = testscheme.New()
+
+type Struct struct {
+	TypeMeta int
+
+	// +k8s:optional
+	// +default="foobar"
+	StringField string `json:"stringField"`
+
+	// +k8s:optional
+	// +default="foobar"
+	StringPtrField *string `json:"stringPtrField"`
+
+	// +k8s:optional
+	// +default=123
+	IntField int `json:"intField"`
+
+	// +k8s:optional
+	// +default=123
+	IntPtrField *int `json:"intPtrField"`
+
+	// +k8s:optional
+	// +default=true
+	BoolField bool `json:"boolField"`
+
+	// +k8s:optional
+	// +default=true
+	BoolPtrField *bool `json:"boolPtrField"`
+}

staging/src/k8s.io/code-generator/cmd/validation-gen/output_tests/tags/optional/nonzero_defaults/doc_test.go

@@ -0,0 +1,47 @@
+/*
+Copyright 2024 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 nonzerodefaults
+
+import (
+	"testing"
+
+	"k8s.io/utils/ptr"
+)
+
+func Test(t *testing.T) {
+	st := localSchemeBuilder.Test(t)
+
+	st.Value(&Struct{
+		// All zero-values.
+	}).ExpectRegexpsByPath(map[string][]string{
+		"stringField":    {"Required value"},
+		"stringPtrField": {"Required value"},
+		"intField":       {"Required value"},
+		"intPtrField":    {"Required value"},
+		"boolField":      {"Required value"},
+		"boolPtrField":   {"Required value"},
+	})
+
+	st.Value(&Struct{
+		StringField:    "abc",
+		StringPtrField: ptr.To(""),
+		IntField:       123,
+		IntPtrField:    ptr.To(0),
+		BoolField:      true,
+		BoolPtrField:   ptr.To(false),
+	}).ExpectValid()
+}

staging/src/k8s.io/code-generator/cmd/validation-gen/output_tests/tags/optional/nonzero_defaults/zz_generated.validations.go

@@ -0,0 +1,119 @@
+//go:build !ignore_autogenerated
+// +build !ignore_autogenerated
+
+/*
+Copyright 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.
+*/
+
+// Code generated by validation-gen. DO NOT EDIT.
+
+package nonzerodefaults
+
+import (
+	context "context"
+	fmt "fmt"
+
+	operation "k8s.io/apimachinery/pkg/api/operation"
+	safe "k8s.io/apimachinery/pkg/api/safe"
+	validate "k8s.io/apimachinery/pkg/api/validate"
+	field "k8s.io/apimachinery/pkg/util/validation/field"
+	testscheme "k8s.io/code-generator/cmd/validation-gen/testscheme"
+)
+
+func init() { localSchemeBuilder.Register(RegisterValidations) }
+
+// RegisterValidations adds validation functions to the given scheme.
+// Public to allow building arbitrary schemes.
+func RegisterValidations(scheme *testscheme.Scheme) error {
+	scheme.AddValidationFunc((*Struct)(nil), func(ctx context.Context, op operation.Operation, obj, oldObj interface{}, subresources ...string) field.ErrorList {
+		if len(subresources) == 0 {
+			return Validate_Struct(ctx, op, nil /* fldPath */, obj.(*Struct), safe.Cast[*Struct](oldObj))
+		}
+		return field.ErrorList{field.InternalError(nil, fmt.Errorf("no validation found for %T, subresources: %v", obj, subresources))}
+	})
+	return nil
+}
+
+func Validate_Struct(ctx context.Context, op operation.Operation, fldPath *field.Path, obj, oldObj *Struct) (errs field.ErrorList) {
+	// field Struct.TypeMeta has no validation
+
+	// field Struct.StringField
+	errs = append(errs,
+		func(fldPath *field.Path, obj, oldObj *string) (errs field.ErrorList) {
+			// optional fields with default values are effectively required
+			if e := validate.RequiredValue(ctx, op, fldPath, obj, oldObj); len(e) != 0 {
+				errs = append(errs, e...)
+				return // do not proceed
+			}
+			return
+		}(fldPath.Child("stringField"), &obj.StringField, safe.Field(oldObj, func(oldObj *Struct) *string { return &oldObj.StringField }))...)
+
+	// field Struct.StringPtrField
+	errs = append(errs,
+		func(fldPath *field.Path, obj, oldObj *string) (errs field.ErrorList) {
+			// optional fields with default values are effectively required
+			if e := validate.RequiredPointer(ctx, op, fldPath, obj, oldObj); len(e) != 0 {
+				errs = append(errs, e...)
+				return // do not proceed
+			}
+			return
+		}(fldPath.Child("stringPtrField"), obj.StringPtrField, safe.Field(oldObj, func(oldObj *Struct) *string { return oldObj.StringPtrField }))...)
+
+	// field Struct.IntField
+	errs = append(errs,
+		func(fldPath *field.Path, obj, oldObj *int) (errs field.ErrorList) {
+			// optional fields with default values are effectively required
+			if e := validate.RequiredValue(ctx, op, fldPath, obj, oldObj); len(e) != 0 {
+				errs = append(errs, e...)
+				return // do not proceed
+			}
+			return
+		}(fldPath.Child("intField"), &obj.IntField, safe.Field(oldObj, func(oldObj *Struct) *int { return &oldObj.IntField }))...)
+
+	// field Struct.IntPtrField
+	errs = append(errs,
+		func(fldPath *field.Path, obj, oldObj *int) (errs field.ErrorList) {
+			// optional fields with default values are effectively required
+			if e := validate.RequiredPointer(ctx, op, fldPath, obj, oldObj); len(e) != 0 {
+				errs = append(errs, e...)
+				return // do not proceed
+			}
+			return
+		}(fldPath.Child("intPtrField"), obj.IntPtrField, safe.Field(oldObj, func(oldObj *Struct) *int { return oldObj.IntPtrField }))...)
+
+	// field Struct.BoolField
+	errs = append(errs,
+		func(fldPath *field.Path, obj, oldObj *bool) (errs field.ErrorList) {
+			// optional fields with default values are effectively required
+			if e := validate.RequiredValue(ctx, op, fldPath, obj, oldObj); len(e) != 0 {
+				errs = append(errs, e...)
+				return // do not proceed
+			}
+			return
+		}(fldPath.Child("boolField"), &obj.BoolField, safe.Field(oldObj, func(oldObj *Struct) *bool { return &oldObj.BoolField }))...)
+
+	// field Struct.BoolPtrField
+	errs = append(errs,
+		func(fldPath *field.Path, obj, oldObj *bool) (errs field.ErrorList) {
+			// optional fields with default values are effectively required
+			if e := validate.RequiredPointer(ctx, op, fldPath, obj, oldObj); len(e) != 0 {
+				errs = append(errs, e...)
+				return // do not proceed
+			}
+			return
+		}(fldPath.Child("boolPtrField"), obj.BoolPtrField, safe.Field(oldObj, func(oldObj *Struct) *bool { return oldObj.BoolPtrField }))...)
+
+	return errs
+}

staging/src/k8s.io/code-generator/cmd/validation-gen/output_tests/tags/optional/zero_defaults/doc.go

@@ -0,0 +1,53 @@
+/*
+Copyright 2025 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.
+*/
+
+// +k8s:validation-gen=TypeMeta
+// +k8s:validation-gen-scheme-registry=k8s.io/code-generator/cmd/validation-gen/testscheme.Scheme
+
+// This is a test package.
+package zerodefaults
+
+import "k8s.io/code-generator/cmd/validation-gen/testscheme"
+
+var localSchemeBuilder = testscheme.New()
+
+type Struct struct {
+	TypeMeta int
+
+	// +k8s:optional
+	// +default=""
+	StringField string `json:"stringField"`
+
+	// +k8s:optional
+	// +default=""
+	StringPtrField *string `json:"stringPtrField"`
+
+	// +k8s:optional
+	// +default=0
+	IntField int `json:"intField"`
+
+	// +k8s:optional
+	// +default=0
+	IntPtrField *int `json:"intPtrField"`
+
+	// +k8s:optional
+	// +default=false
+	BoolField bool `json:"boolField"`
+
+	// +k8s:optional
+	// +default=false
+	BoolPtrField *bool `json:"boolPtrField"`
+}

staging/src/k8s.io/code-generator/cmd/validation-gen/output_tests/tags/optional/zero_defaults/doc_test.go

@@ -0,0 +1,47 @@
+/*
+Copyright 2024 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 zerodefaults
+
+import (
+	"testing"
+
+	"k8s.io/utils/ptr"
+)
+
+func Test(t *testing.T) {
+	st := localSchemeBuilder.Test(t)
+
+	st.Value(&Struct{
+		// All zero-values.
+	}).ExpectRegexpsByPath(map[string][]string{
+		// "stringField": optional value fields with zero defaults are just docs
+		// "intField": optional value fields with zero defaults are just docs
+		// "boolField": optional value fields with zero defaults are just docs
+		"stringPtrField": {"Required value"},
+		"intPtrField":    {"Required value"},
+		"boolPtrField":   {"Required value"},
+	})
+
+	st.Value(&Struct{
+		StringField:    "abc",
+		StringPtrField: ptr.To(""),
+		IntField:       123,
+		IntPtrField:    ptr.To(0),
+		BoolField:      true,
+		BoolPtrField:   ptr.To(false),
+	}).ExpectValid()
+}

staging/src/k8s.io/code-generator/cmd/validation-gen/output_tests/tags/optional/zero_defaults/zz_generated.validations.go

@@ -0,0 +1,107 @@
+//go:build !ignore_autogenerated
+// +build !ignore_autogenerated
+
+/*
+Copyright 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.
+*/
+
+// Code generated by validation-gen. DO NOT EDIT.
+
+package zerodefaults
+
+import (
+	context "context"
+	fmt "fmt"
+
+	operation "k8s.io/apimachinery/pkg/api/operation"
+	safe "k8s.io/apimachinery/pkg/api/safe"
+	validate "k8s.io/apimachinery/pkg/api/validate"
+	field "k8s.io/apimachinery/pkg/util/validation/field"
+	testscheme "k8s.io/code-generator/cmd/validation-gen/testscheme"
+)
+
+func init() { localSchemeBuilder.Register(RegisterValidations) }
+
+// RegisterValidations adds validation functions to the given scheme.
+// Public to allow building arbitrary schemes.
+func RegisterValidations(scheme *testscheme.Scheme) error {
+	scheme.AddValidationFunc((*Struct)(nil), func(ctx context.Context, op operation.Operation, obj, oldObj interface{}, subresources ...string) field.ErrorList {
+		if len(subresources) == 0 {
+			return Validate_Struct(ctx, op, nil /* fldPath */, obj.(*Struct), safe.Cast[*Struct](oldObj))
+		}
+		return field.ErrorList{field.InternalError(nil, fmt.Errorf("no validation found for %T, subresources: %v", obj, subresources))}
+	})
+	return nil
+}
+
+func Validate_Struct(ctx context.Context, op operation.Operation, fldPath *field.Path, obj, oldObj *Struct) (errs field.ErrorList) {
+	// field Struct.TypeMeta has no validation
+
+	// field Struct.StringField
+	errs = append(errs,
+		func(fldPath *field.Path, obj, oldObj *string) (errs field.ErrorList) {
+			// optional value-type fields with zero-value defaults are purely documentation
+			return
+		}(fldPath.Child("stringField"), &obj.StringField, safe.Field(oldObj, func(oldObj *Struct) *string { return &oldObj.StringField }))...)
+
+	// field Struct.StringPtrField
+	errs = append(errs,
+		func(fldPath *field.Path, obj, oldObj *string) (errs field.ErrorList) {
+			// optional fields with default values are effectively required
+			if e := validate.RequiredPointer(ctx, op, fldPath, obj, oldObj); len(e) != 0 {
+				errs = append(errs, e...)
+				return // do not proceed
+			}
+			return
+		}(fldPath.Child("stringPtrField"), obj.StringPtrField, safe.Field(oldObj, func(oldObj *Struct) *string { return oldObj.StringPtrField }))...)
+
+	// field Struct.IntField
+	errs = append(errs,
+		func(fldPath *field.Path, obj, oldObj *int) (errs field.ErrorList) {
+			// optional value-type fields with zero-value defaults are purely documentation
+			return
+		}(fldPath.Child("intField"), &obj.IntField, safe.Field(oldObj, func(oldObj *Struct) *int { return &oldObj.IntField }))...)
+
+	// field Struct.IntPtrField
+	errs = append(errs,
+		func(fldPath *field.Path, obj, oldObj *int) (errs field.ErrorList) {
+			// optional fields with default values are effectively required
+			if e := validate.RequiredPointer(ctx, op, fldPath, obj, oldObj); len(e) != 0 {
+				errs = append(errs, e...)
+				return // do not proceed
+			}
+			return
+		}(fldPath.Child("intPtrField"), obj.IntPtrField, safe.Field(oldObj, func(oldObj *Struct) *int { return oldObj.IntPtrField }))...)
+
+	// field Struct.BoolField
+	errs = append(errs,
+		func(fldPath *field.Path, obj, oldObj *bool) (errs field.ErrorList) {
+			// optional value-type fields with zero-value defaults are purely documentation
+			return
+		}(fldPath.Child("boolField"), &obj.BoolField, safe.Field(oldObj, func(oldObj *Struct) *bool { return &oldObj.BoolField }))...)
+
+	// field Struct.BoolPtrField
+	errs = append(errs,
+		func(fldPath *field.Path, obj, oldObj *bool) (errs field.ErrorList) {
+			// optional fields with default values are effectively required
+			if e := validate.RequiredPointer(ctx, op, fldPath, obj, oldObj); len(e) != 0 {
+				errs = append(errs, e...)
+				return // do not proceed
+			}
+			return
+		}(fldPath.Child("boolPtrField"), obj.BoolPtrField, safe.Field(oldObj, func(oldObj *Struct) *bool { return oldObj.BoolPtrField }))...)
+
+	return errs
+}

staging/src/k8s.io/code-generator/cmd/validation-gen/validators/required.go

@@ -17,16 +17,21 @@ limitations under the License.
 package validators
 
 import (
+	"encoding/json"
 	"fmt"
+	"reflect"
+
+	"k8s.io/gengo/v2"
+	"k8s.io/gengo/v2/types"
 
 	"k8s.io/apimachinery/pkg/util/sets"
-	"k8s.io/gengo/v2/types"
 )
 
 const (
 	requiredTagName  = "k8s:required"
 	optionalTagName  = "k8s:optional"
 	forbiddenTagName = "k8s:forbidden"
+	defaultTagName   = "default" // TODO: this should evenually be +k8s:default
 )
 
 func init() {
@@ -84,7 +89,7 @@ var (
 
 // TODO: It might be valuable to have a string payload for when requiredness is
 // conditional (e.g. required when <otherfield> is specified).
-func (requirednessTagValidator) doRequired(context Context) (Validations, error) {
+func (rtv requirednessTagValidator) doRequired(context Context) (Validations, error) {
 	// Most validators don't care whether the value they are validating was
 	// originally defined as a value-type or a pointer-type in the API.  This
 	// one does.  Since Go doesn't do partial specialization of templates, we
@@ -114,7 +119,48 @@ var (
 	optionalMapValidator     = types.Name{Package: libValidationPkg, Name: "OptionalMap"}
 )
 
-func (requirednessTagValidator) doOptional(context Context) (Validations, error) {
+func (rtv requirednessTagValidator) doOptional(context Context) (Validations, error) {
+	// All of our tags are expressed from the perspective of a client of the
+	// API, but the code we generate is for the server. Optional is tricky.
+	//
+	// A field which is marked as optional and does not have a default is
+	// strictly optional. A client is allowed to not set it and the server will
+	// not give it a default value. Code which consumes it must handle that it
+	// might not have any value at all.
+	//
+	// A field which is marked as optional but has a default is optional to
+	// clients, but required to the server. A client is allowed to not set it
+	// but the server will give it a default value. Code which consumes it can
+	// assume that it always has a value.
+	//
+	// One special case must be handled: optional non-pointer fields with
+	// default values. If the default is not the zero value for the type, then
+	// the zero value is used to decide whether to assign the default value,
+	// and so must be out of bounds; we can proceed as above.
+	//
+	// But if the default is the zero value, then the zero value is obviously
+	// valid, and the fact that the field is optional is meaningless - there is
+	// no way to tell the difference between a client not setting it (yielding
+	// the zero value) and a client setting it to the zero value.
+	//
+	// TODO: handle default=ref(...)
+	// TODO: handle manual defaulting
+	if hasDefault, zeroDefault, err := rtv.hasZeroDefault(context); err != nil {
+		return Validations{}, err
+	} else if hasDefault {
+		if !isNilableType(context.Type) && zeroDefault {
+			return Validations{Comments: []string{"optional value-type fields with zero-value defaults are purely documentation"}}, nil
+		}
+		validations, err := rtv.doRequired(context)
+		if err != nil {
+			return Validations{}, err
+		}
+		for i, fn := range validations.Functions {
+			validations.Functions[i] = WithComment(fn, "optional fields with default values are effectively required")
+		}
+		return validations, nil
+	}
+
 	// Most validators don't care whether the value they are validating was
 	// originally defined as a value-type or a pointer-type in the API.  This
 	// one does.  Since Go doesn't do partial specialization of templates, we
@@ -137,6 +183,71 @@ func (requirednessTagValidator) doOptional(context Context) (Validations, error)
 	return Validations{Functions: []FunctionGen{Function(optionalTagName, ShortCircuit|NonError, optionalValueValidator)}}, nil
 }
 
+// hasZeroDefault returns whether the field has a default value and whether
+// that default value is the zero value for the field's type.
+func (rtv requirednessTagValidator) hasZeroDefault(context Context) (bool, bool, error) {
+	t := realType(context.Type)
+	// This validator only applies to fields, so Member must be valid.
+	tagsByName, err := gengo.ExtractFunctionStyleCommentTags("+", []string{defaultTagName}, context.Member.CommentLines)
+	if err != nil {
+		return false, false, fmt.Errorf("failed to read tags: %w", err)
+	}
+
+	tags, hasDefault := tagsByName[defaultTagName]
+	if !hasDefault {
+		return false, false, nil
+	}
+	if len(tags) == 0 {
+		return false, false, fmt.Errorf("+default tag with no value")
+	}
+	if len(tags) > 1 {
+		return false, false, fmt.Errorf("+default tag with multiple values: %q", tags)
+	}
+
+	payload := tags[0].Value
+	var defaultValue any
+	if err := json.Unmarshal([]byte(payload), &defaultValue); err != nil {
+		return false, false, fmt.Errorf("failed to parse default value %q: %w", payload, err)
+	}
+	if defaultValue == nil {
+		return false, false, fmt.Errorf("failed to parse default value %q: unmarshalled to nil", payload)
+	}
+
+	zero, found := typeZeroValue[t.String()]
+	if !found {
+		return false, false, fmt.Errorf("unknown zero-value for type %s", t.String())
+	}
+
+	return true, reflect.DeepEqual(defaultValue, zero), nil
+}
+
+// This is copied from defaulter-gen.
+// TODO: move this back to gengo as Type.ZeroValue()?
+var typeZeroValue = map[string]any{
+	"uint":        0.,
+	"uint8":       0.,
+	"uint16":      0.,
+	"uint32":      0.,
+	"uint64":      0.,
+	"int":         0.,
+	"int8":        0.,
+	"int16":       0.,
+	"int32":       0.,
+	"int64":       0.,
+	"byte":        0.,
+	"float64":     0.,
+	"float32":     0.,
+	"bool":        false,
+	"time.Time":   "",
+	"string":      "",
+	"integer":     0.,
+	"number":      0.,
+	"boolean":     false,
+	"[]byte":      "", // base64 encoded characters
+	"interface{}": interface{}(nil),
+	"any":         interface{}(nil),
+}
+
 var (
 	forbiddenValueValidator   = types.Name{Package: libValidationPkg, Name: "ForbiddenValue"}
 	forbiddenPointerValidator = types.Name{Package: libValidationPkg, Name: "ForbiddenPointer"}

staging/src/k8s.io/code-generator/cmd/validation-gen/validators/validators.go

@@ -17,10 +17,11 @@ limitations under the License.
 package validators
 
 import (
-	"k8s.io/apimachinery/pkg/util/sets"
-	"k8s.io/apimachinery/pkg/util/validation/field"
 	"k8s.io/gengo/v2/generator"
 	"k8s.io/gengo/v2/types"
+
+	"k8s.io/apimachinery/pkg/util/sets"
+	"k8s.io/apimachinery/pkg/util/validation/field"
 )
 
 // TagValidator describes a single validation tag and how to use it.