Add validators: opaque

Skips validation of a type's tags.

Co-authored-by: Tim Hockin <thockin@google.com>
Co-authored-by: Aaron Prindle <aprindle@google.com>
Co-authored-by: Yongrui Lin <yongrlin@google.com>

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

@@ -0,0 +1,56 @@
+/*
+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 validators
+
+import "k8s.io/apimachinery/pkg/util/sets"
+
+const (
+	opaqueTypeTagName = "k8s:opaqueType"
+)
+
+type opaqueTypeTagValidator struct{}
+
+func init() {
+	RegisterTagValidator(opaqueTypeTagValidator{})
+}
+
+func (opaqueTypeTagValidator) Init(Config) {}
+
+func (opaqueTypeTagValidator) TagName() string {
+	return opaqueTypeTagName
+}
+
+func (opaqueTypeTagValidator) ValidScopes() sets.Set[Scope] {
+	return sets.New(ScopeAny)
+}
+
+func (opaqueTypeTagValidator) GetValidations(context Context, _ []string, _ string) (Validations, error) {
+	return Validations{OpaqueType: true}, nil
+}
+
+func (opaqueTypeTagValidator) Docs() TagDoc {
+	doc := TagDoc{
+		Tag:    opaqueTypeTagName,
+		Scopes: []Scope{ScopeField},
+		Description: "Indicates that any validations declared on the referenced type will be ignored. " +
+			"If a referenced type's package is not included in the generator's current " +
+			"flags, this tag must be set, or code generation will fail (preventing silent " +
+			"mistakes). If the validations should not be ignored, add the type's package " +
+			"to the generator using the --extra-pkg flag.",
+	}
+	return doc
+}