[go-server] Feat: add required assertions to models (#10068)

* Add RequiredError

* Add IsZeroValue helper

* Add AssertRequired method to all models

* Add AssertRequired call for body param

* Regenerate files

* Add DisallowUnknownFields

* Regenerate samples

* Use hasRequired in model to remove unnecessary code

* Revert disallowUnknownFields

* Use isAdditionalPropertiesTrue for disallowing unknown fields

* Updated samples

* Fix indent

* Add require checks for nested slices

* Add new tests

* Regenerate samples

* Regenerate samples after merging

samples/server/petstore/go-server-required/go/helpers.go

@@ -0,0 +1,64 @@
+/*
+ * OpenAPI Petstore
+ *
+ * This is a sample server Petstore server. For this sample, you can use the api key `special-key` to test the authorization filters.
+ *
+ * API version: 1.0.0
+ * Generated by: OpenAPI Generator (https://openapi-generator.tech)
+ */
+
+package petstoreserver
+
+import (
+	"reflect"
+)
+
+// Response return a ImplResponse struct filled
+func Response(code int, body interface{}) ImplResponse {
+	return ImplResponse {
+		Code: code,
+		Headers: nil,
+		Body: body,
+	}
+}
+
+// ResponseWithHeaders return a ImplResponse struct filled, including headers
+func ResponseWithHeaders(code int, headers map[string][]string, body interface{}) ImplResponse {
+	return ImplResponse {
+		Code: code,
+		Headers: headers,
+		Body: body,
+	}
+}
+
+// IsZeroValue checks if the val is the zero-ed value.
+func IsZeroValue(val interface{}) bool {
+	return val == nil || reflect.DeepEqual(val, reflect.Zero(reflect.TypeOf(val)).Interface())
+}
+
+// AssertInterfaceRequired recursively checks each struct in a slice against the callback.
+// This method traverse nested slices in a preorder fashion.
+func AssertRecurseInterfaceRequired(obj interface{}, callback func(interface{}) error) error {
+	return AssertRecurseValueRequired(reflect.ValueOf(obj), callback)
+}
+
+// AssertNestedValueRequired checks each struct in the nested slice against the callback.
+// This method traverse nested slices in a preorder fashion.
+func AssertRecurseValueRequired(value reflect.Value, callback func(interface{}) error) error {
+	switch value.Kind() {
+	// If it is a struct we check using callback
+	case reflect.Struct:
+		if err := callback(value.Interface()); err != nil {
+			return err
+		}
+
+	// If it is a slice we continue recursion
+	case reflect.Slice:
+		for i := 0; i < value.Len(); i += 1 {
+			if err := AssertRecurseValueRequired(value.Index(i), callback); err != nil {
+				return err
+			}
+		}
+	}
+	return nil
+}