feat: add support for controlling "omitempty" via x-omitempty extension (#276)

Co-authored-by: Vragov Roman <vragov@retailcrm.ru>

Author: vragovR

README.md

@@ -740,6 +740,32 @@ These extension properties apply to "Schema Objects" in AsyncAPI spec.
   }
   ```
 
+* `x-omitempty`: Controls the addition of the `omitempty` tag in JSON tags of generated Go structures.
+  When set to `false`, the `omitempty` tag won't be added even for optional fields.
+
+  For example,
+
+  ```yaml
+  schemas:
+    User:
+      type: object
+      properties:
+        id:
+          type: string
+        name:
+          type: string
+          x-omitempty: false
+  ```
+
+  will be generated as
+
+  ```go
+  type User struct {
+      Id   *string `json:"id,omitempty"`
+      Name *string `json:"name"`
+  }
+  ```
+
 ### ErrorHandler
 
 You can use an error handler that will be executed when processing for messages
@@ -773,7 +799,7 @@ ctrl, _ := NewAppController(/* Broker of your choice */, WithErrorHandler(errorh
 func(ctx context.Context, topic string, msg *extensions.AcknowledgeableBrokerMessage, err error) {
     // check error or move message to some other queue/topic
     handleTheErrorSomehow()
-    
+
     // Ack or Nak the message
     msg.Ack()
     msg.Nak()

pkg/asyncapi/schema.go

@@ -25,12 +25,13 @@ type Validations[T any] struct {
 	OneOf []*T `json:"oneOf"`
 
 	// --- Non JSON Schema/AsyncAPI fields -------------------------------------
-	IsRequired bool `json:"-"`
+	IsRequired      bool  `json:"-"`
+	ShouldOmitEmpty *bool `json:"-"`
 }
 
 // Merge merges the newV into the current Validations.
 //
-//nolint:cyclop // This function is a merge function and it is expected to have a high cyclomatic complexity.
+//nolint:cyclop,funlen // This function is a merge function and it is expected to have a high cyclomatic complexity.
 func (v *Validations[T]) Merge(newV Validations[T]) {
 	if len(newV.Required) > 0 {
 		v.Required = newV.Required
@@ -92,4 +93,7 @@ func (v *Validations[T]) Merge(newV Validations[T]) {
 	if newV.IsRequired {
 		v.IsRequired = newV.IsRequired
 	}
+	if newV.ShouldOmitEmpty != nil {
+		v.ShouldOmitEmpty = newV.ShouldOmitEmpty
+	}
 }

pkg/asyncapi/v2/extensions.go

@@ -13,6 +13,10 @@ type Extensions struct {
 
 	// Setting custom import statements for ExtGoType
 	ExtGoTypeImport *GoTypeImportExtension `json:"x-go-type-import"`
+
+	// Controls whether to include omitempty in JSON tags
+	// If false, omitempty will be removed from JSON tags even if the field can be null
+	ExtOmitEmpty *bool `json:"x-omitempty"`
 }
 
 // GoTypeImportExtension specifies the required import statement

pkg/asyncapi/v2/schema.go

@@ -101,6 +101,9 @@ func (s *Schema) generateMetadata(name string, isRequired bool) error {
 			s.Type = "string"
 		}
 	}
+
+	s.ShouldOmitEmpty = s.ExtOmitEmpty
+
 	return nil
 }
 

pkg/asyncapi/v3/extensions.go

@@ -13,6 +13,10 @@ type Extensions struct {
 
 	// Setting custom import statements for ExtGoType
 	ExtGoTypeImport *GoTypeImportExtension `json:"x-go-type-import"`
+
+	// Controls whether to include omitempty in JSON tags
+	// If false, omitempty will be removed from JSON tags even if the field can be null
+	ExtOmitEmpty *bool `json:"x-omitempty"`
 }
 
 // GoTypeImportExtension specifies the required import statement

pkg/asyncapi/v3/schema.go

@@ -161,6 +161,8 @@ func (s *Schema) generateMetadata(parentName, name string, number *int, isRequir
 	// Set IsRequired
 	s.IsRequired = isRequired
 
+	s.ShouldOmitEmpty = s.ExtOmitEmpty
+
 	return nil
 }
 

pkg/codegen/generators/helpers.go

@@ -21,13 +21,21 @@ func GenerateJSONTags[T any](schema asyncapi.Validations[T], field string) strin
 		template.ConvertKey(field),
 	}
 
-	if !schema.IsRequired {
+	if shouldAddOmitEmpty(schema) {
 		directives = append(directives, "omitempty")
 	}
 
 	return fmt.Sprintf("json:\"%s\"", strings.Join(directives, ","))
 }
 
+func shouldAddOmitEmpty[T any](schema asyncapi.Validations[T]) bool {
+	if schema.IsRequired {
+		return schema.ShouldOmitEmpty != nil && *schema.ShouldOmitEmpty
+	}
+
+	return schema.ShouldOmitEmpty == nil || *schema.ShouldOmitEmpty
+}
+
 // GenerateValidateTags returns the "validate" tag for a given field in a struct, based on the asyncapi contract.
 // This tag can then be used by go-playground/validator/v10 to validate the struct's content.
 func GenerateValidateTags[T any](schema asyncapi.Validations[T], isPointer bool, schemaType string) string {

test/v2/issues/275/asyncapi.gen.go

@@ -0,0 +1,30 @@
+asyncapi: 2.6.0
+info:
+  title: OmitEmpty Test
+  version: 1.0.0
+
+channels:
+  v2.omitempty.test:
+    subscribe:
+      message:
+        payload:
+          $ref: '#/components/schemas/Test'
+
+components:
+  schemas:
+    Test:
+      type: object
+      required:
+        - requiredWithOmitEmpty
+      properties:
+        withOmitEmpty:
+          type: string
+          description: "This field should have omitempty in the JSON tag"
+        withoutOmitEmpty:
+          type: string
+          description: "This field should NOT have omitempty in the JSON tag"
+          x-omitempty: false
+        requiredWithOmitEmpty:
+          type: string
+          description: "This field should have omitempty in the JSON tag"
+          x-omitempty: true

test/v2/issues/275/asyncapi.yaml

@@ -0,0 +1,30 @@
+//go:generate go run ../../../../cmd/asyncapi-codegen -p issue275 -g types -i ./asyncapi.yaml -o ./asyncapi.gen.go
+
+package issue275
+
+import (
+	"encoding/json"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/suite"
+)
+
+func TestSuite(t *testing.T) {
+	suite.Run(t, NewSuite())
+}
+
+type Suite struct {
+	suite.Suite
+}
+
+func NewSuite() *Suite {
+	return &Suite{}
+}
+
+func (suite *Suite) TestMarshal_OmitEmpty() {
+	var res TestSchema
+	data, err := json.Marshal(res)
+	assert.NoError(suite.T(), err)
+	assert.JSONEq(suite.T(), "{\"withoutOmitEmpty\":null}", string(data))
+}