Add validator to kustomization

api/internal/plugins/execplugin/execplugin.go

@@ -140,6 +140,11 @@ func (p *ExecPlugin) Transform(rm resmap.ResMap) error {
 	return p.updateResMapValues(output, rm)
 }
 
+func (p *ExecPlugin) Validate(rm resmap.ResMap) error {
+	// Validate works exactly same with Transformer
+	return p.Transform(rm)
+}
+
 // invokePlugin writes plugin config to a temp file, then
 // passes the full temp file path as the first arg to a process
 // running the plugin binary.  Process output is returned.

api/internal/plugins/loader/loader.go

@@ -87,6 +87,32 @@ func (l *Loader) LoadTransformer(
 	return t, nil
 }
 
+func (l *Loader) LoadValidators(
+	ldr ifc.Loader, v ifc.Validator, rm resmap.ResMap) ([]resmap.Validator, error) {
+	var result []resmap.Validator
+	for _, res := range rm.Resources() {
+		t, err := l.LoadValidator(ldr, v, res)
+		if err != nil {
+			return nil, err
+		}
+		result = append(result, t)
+	}
+	return result, nil
+}
+
+func (l *Loader) LoadValidator(
+	ldr ifc.Loader, v ifc.Validator, res *resource.Resource) (resmap.Validator, error) {
+	c, err := l.loadAndConfigurePlugin(ldr, v, res)
+	if err != nil {
+		return nil, err
+	}
+	t, ok := c.(resmap.Validator)
+	if !ok {
+		return nil, fmt.Errorf("plugin %s not a validator", res.OrgId())
+	}
+	return t, nil
+}
+
 func relativePluginPath(id resid.ResId) string {
 	return filepath.Join(
 		id.Group,

api/internal/target/kusttarget.go

@@ -209,6 +209,10 @@ func (kt *KustTarget) accumulateTarget(ra *accumulator.ResAccumulator) (
 	if err != nil {
 		return nil, err
 	}
+	err = kt.runValidators(ra)
+	if err != nil {
+		return nil, err
+	}
 	err = ra.MergeVars(kt.kustomization.Vars)
 	if err != nil {
 		return nil, errors.Wrapf(
@@ -278,6 +282,29 @@ func (kt *KustTarget) configureExternalTransformers() ([]resmap.Transformer, err
 	return kt.pLdr.LoadTransformers(kt.ldr, kt.validator, ra.ResMap())
 }
 
+func (kt *KustTarget) runValidators(ra *accumulator.ResAccumulator) error {
+	validators, err := kt.configureExternalValidators()
+	if err != nil {
+		return err
+	}
+	for _, v := range validators {
+		err := v.Validate(ra.ResMap())
+		if err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func (kt *KustTarget) configureExternalValidators() ([]resmap.Validator, error) {
+	ra := accumulator.MakeEmptyAccumulator()
+	ra, err := kt.accumulateResources(ra, kt.kustomization.Validators)
+	if err != nil {
+		return nil, err
+	}
+	return kt.pLdr.LoadValidators(kt.ldr, kt.validator, ra.ResMap())
+}
+
 // accumulateResources fills the given resourceAccumulator
 // with resources read from the given list of paths.
 func (kt *KustTarget) accumulateResources(