Enable validation using function config schema from KRMFunctionDefinition

kyaml/fn/framework/validation.go

@@ -0,0 +1,36 @@
+// Copyright 2022 The Kubernetes Authors.
+// SPDX-License-Identifier: Apache-2.0
+
+package framework
+
+import (
+	"k8s.io/kube-openapi/pkg/validation/spec"
+	"sigs.k8s.io/kustomize/kyaml/errors"
+	"sigs.k8s.io/kustomize/kyaml/resid"
+	k8syaml "sigs.k8s.io/yaml"
+)
+
+// SchemaFromFunctionDefinition extracts the schema for a particular GVK from the provided KRMFunctionDefinition
+// Since the relevant fields of KRMFunctionDefinition exactly match the ones in CustomResourceDefinition,
+// this helper can also load CRDs (e.g. produced by KubeBuilder) transparently.
+func SchemaFromFunctionDefinition(gvk resid.Gvk, data string) (*spec.Schema, error) {
+	var def KRMFunctionDefinition
+	// need to use sigs yaml because spec.Schema type only has json tags
+	if err := k8syaml.Unmarshal([]byte(data), &def); err != nil {
+		return nil, errors.WrapPrefixf(err, "unmarshalling %s", FunctionDefinitionKind)
+	}
+	var foundGVKs []*resid.Gvk
+	var schema *spec.Schema
+	for i, version := range def.Spec.Versions {
+		versionGVK := resid.Gvk{Group: def.Spec.Group, Kind: def.Spec.Names.Kind, Version: version.Name}
+		if gvk.Equals(versionGVK) {
+			schema = def.Spec.Versions[i].Schema.OpenAPIV3Schema
+			break
+		}
+		foundGVKs = append(foundGVKs, &versionGVK)
+	}
+	if schema == nil {
+		return nil, errors.Errorf("%s does not define %s (defines: %s)", FunctionDefinitionKind, gvk, foundGVKs)
+	}
+	return schema, nil
+}