feat: add unique items validator

pkg/runner/registry.go

@@ -42,6 +42,7 @@ func init() {
 	property.RegisterRequired(defaultRegistry)
 	property.RegisterType(defaultRegistry)
 	property.RegisterDescription(defaultRegistry)
+	property.RegisterUniqueItems(defaultRegistry)
 }
 
 // DefaultRegistry returns a pre-configured validations.Registry.

pkg/validations/property/uniqueitems.go

@@ -0,0 +1,88 @@
+// 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.
+
+package property
+
+import (
+	"errors"
+	"fmt"
+
+	apiextensionsv1 "k8s.io/apiextensions-apiserver/pkg/apis/apiextensions/v1"
+	"sigs.k8s.io/crdify/pkg/config"
+	"sigs.k8s.io/crdify/pkg/validations"
+)
+
+var (
+	_ validations.Validation                                  = (*UniqueItems)(nil)
+	_ validations.Comparator[apiextensionsv1.JSONSchemaProps] = (*UniqueItems)(nil)
+)
+
+const uniqueItemsValidationName = "uniqueItems"
+
+// RegisterUniqueItems registers the UniqueItems validation
+// with the provided validation registry.
+func RegisterUniqueItems(registry validations.Registry) {
+	registry.Register(uniqueItemsValidationName, uniqueItemsFactory)
+}
+
+// uniqueItemsFactory is a function used to initialize a UniqueItems validation
+// implementation based on the provided configuration.
+func uniqueItemsFactory(_ map[string]any) (validations.Validation, error) {
+	return &UniqueItems{}, nil
+}
+
+// UniqueItems is a Validation that can be used to identify
+// incompatible changes to the uniqueItems constraints of CRD properties.
+// The uniqueItems constraint enforces that lists should only contain unique items.
+// Going from non-unique to unique is more restrictive and breaking.
+// Going from unique to non-unique is less restrictive and OK.
+type UniqueItems struct {
+	enforcement config.EnforcementPolicy
+}
+
+// Name returns the name of the UniqueItems validation.
+func (u *UniqueItems) Name() string {
+	return uniqueItemsValidationName
+}
+
+// SetEnforcement sets the EnforcementPolicy for the UniqueItems validation.
+func (u *UniqueItems) SetEnforcement(policy config.EnforcementPolicy) {
+	u.enforcement = policy
+}
+
+// Compare compares an old and a new JSONSchemaProps, checking for incompatible changes to the uniqueItems constraints of a property.
+// In order for callers to determine if diffs to a JSONSchemaProps have been handled by this validation
+// the JSONSchemaProps.UniqueItems field will be reset to 'false' as part of this method.
+// It is highly recommended that only copies of the JSONSchemaProps to compare are provided to this method
+// to prevent unintentional modifications.
+func (u *UniqueItems) Compare(a, b *apiextensionsv1.JSONSchemaProps) validations.ComparisonResult {
+	var err error
+
+	// Going from non-unique (false) to unique (true) is breaking
+	if !a.UniqueItems && b.UniqueItems {
+		err = fmt.Errorf("%w", ErrUniqueItemsConstraintAdded)
+	}
+	// Going from unique (true) to non-unique (false) is OK (less restrictive)
+	// No error needed for this case
+
+	a.UniqueItems = false
+	b.UniqueItems = false
+
+	return validations.HandleErrors(u.Name(), u.enforcement, err)
+}
+
+var (
+	// ErrUniqueItemsConstraintAdded represents an error state where a uniqueItems constraint was added to a property.
+	ErrUniqueItemsConstraintAdded = errors.New("uniqueItems constraint added when there was none previously")
+)

pkg/validations/property/uniqueitems_test.go

@@ -0,0 +1,103 @@
+// 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.
+
+package property
+
+import (
+	"testing"
+
+	apiextensionsv1 "k8s.io/apiextensions-apiserver/pkg/apis/apiextensions/v1"
+	internaltesting "sigs.k8s.io/crdify/pkg/validations/internal/testing"
+)
+
+func TestUniqueItems(t *testing.T) {
+	testcases := []internaltesting.Testcase[apiextensionsv1.JSONSchemaProps]{
+		{
+			Name: "no diff, not flagged",
+			Old: &apiextensionsv1.JSONSchemaProps{
+				Type: "array",
+			},
+			New: &apiextensionsv1.JSONSchemaProps{
+				Type: "array",
+			},
+			Flagged:              false,
+			ComparableValidation: &UniqueItems{},
+		},
+		{
+			Name: "uniqueItems constraint added (false to true), flagged",
+			Old: &apiextensionsv1.JSONSchemaProps{
+				Type:        "array",
+				UniqueItems: false,
+			},
+			New: &apiextensionsv1.JSONSchemaProps{
+				Type:        "array",
+				UniqueItems: true,
+			},
+			Flagged:              true,
+			ComparableValidation: &UniqueItems{},
+		},
+		{
+			Name: "uniqueItems constraint removed (true to false), not flagged",
+			Old: &apiextensionsv1.JSONSchemaProps{
+				Type:        "array",
+				UniqueItems: true,
+			},
+			New: &apiextensionsv1.JSONSchemaProps{
+				Type:        "array",
+				UniqueItems: false,
+			},
+			Flagged:              false,
+			ComparableValidation: &UniqueItems{},
+		},
+		{
+			Name: "uniqueItems unchanged (both false), not flagged",
+			Old: &apiextensionsv1.JSONSchemaProps{
+				Type:        "array",
+				UniqueItems: false,
+			},
+			New: &apiextensionsv1.JSONSchemaProps{
+				Type:        "array",
+				UniqueItems: false,
+			},
+			Flagged:              false,
+			ComparableValidation: &UniqueItems{},
+		},
+		{
+			Name: "uniqueItems unchanged (both true), not flagged",
+			Old: &apiextensionsv1.JSONSchemaProps{
+				Type:        "array",
+				UniqueItems: true,
+			},
+			New: &apiextensionsv1.JSONSchemaProps{
+				Type:        "array",
+				UniqueItems: true,
+			},
+			Flagged:              false,
+			ComparableValidation: &UniqueItems{},
+		},
+		{
+			Name: "different field changed, not flagged",
+			Old: &apiextensionsv1.JSONSchemaProps{
+				ID: "foo",
+			},
+			New: &apiextensionsv1.JSONSchemaProps{
+				ID: "bar",
+			},
+			Flagged:              false,
+			ComparableValidation: &UniqueItems{},
+		},
+	}
+
+	internaltesting.RunTestcases(t, testcases...)
+}