feat(crdvalidation): add messageExpression support to XValidation marker

pkg/crd/markers/validation.go

@@ -309,8 +309,9 @@ func isIntegral(value float64) bool {
 // This marker may be repeated to specify multiple expressions, all of
 // which must evaluate to true.
 type XValidation struct {
-	Rule    string
-	Message string `marker:",optional"`
+	Rule              string
+	Message           string `marker:",optional"`
+	MessageExpression string `marker:"messageExpression,optional"`
 }
 
 func (m Maximum) ApplyToSchema(schema *apiext.JSONSchemaProps) error {
@@ -534,8 +535,9 @@ func (m XIntOrString) ApplyPriority() ApplyPriority {
 
 func (m XValidation) ApplyToSchema(schema *apiext.JSONSchemaProps) error {
 	schema.XValidations = append(schema.XValidations, apiext.ValidationRule{
-		Rule:    m.Rule,
-		Message: m.Message,
+		Rule:              m.Rule,
+		Message:           m.Message,
+		MessageExpression: m.MessageExpression,
 	})
 	return nil
 }

pkg/crd/testdata/cronjob_types.go

@@ -247,6 +247,10 @@ type CronJobSpec struct {
 	// +kubebuilder:validation:XValidation:rule="true"
 	StringWithEvenLength string `json:"stringWithEvenLength,omitempty"`
 
+	// Test of the expression-based validation with messageExpression marker.
+	// +kubebuilder:validation:XValidation:rule="self.size() % 2 == 0",messageExpression="'Length has to be even but is ' + len(self.stringWithEvenLengthAndMessageExpression) + ' instead'"
+	StringWithEvenLengthAndMessageExpression string `json:"stringWithEvenLengthAndMessageExpression,omitempty"`
+
 	// Checks that fixed-length arrays work
 	Array [3]int `json:"array,omitempty"`
 
@@ -336,7 +340,6 @@ type MinMaxObject struct {
 }
 
 type EmpiableObject struct {
-
 	// +kubebuilder:default=forty-two
 	Foo string `json:"foo,omitempty"`
 	Bar string `json:"bar,omitempty"`

pkg/crd/testdata/testdata.kubebuilder.io_cronjobs.yaml

@@ -6805,6 +6805,13 @@ spec:
                 - message: must have even length
                   rule: self.size() % 2 == 0
                 - rule: "true"
+              stringWithEvenLengthAndMessageExpression:
+                description: Test of the expression-based validation with
+                  messageExpression marker.
+                type: string
+                x-kubernetes-validations:
+                - messageExpression: "'Length has to be even but is ' + len(self.stringWithEvenLengthAndMessageExpression) + ' instead'"
+                  rule: self.size() % 2 == 0
               structWithSeveralFields:
                 description: A struct that can only be entirely replaced
                 properties: