[scala-sttp4] Omit optional fields set to None instead of serializing null (circe)

modules/openapi-generator/src/main/resources/scala-sttp4/model.mustache

@@ -51,7 +51,7 @@ object {{classname}} {
   import io.circe.syntax._
   import io.circe.generic.semiauto._
 
-  implicit val encoder: Encoder[{{classname}}] = deriveEncoder
+  implicit val encoder: Encoder[{{classname}}] = deriveEncoder[{{classname}}].mapJson(_.dropNullValues)
   implicit val decoder: Decoder[{{classname}}] = deriveDecoder
 }
 {{/circe}}
@@ -180,7 +180,7 @@ object {{classname}} {
   import io.circe.{Encoder, Decoder}
   import io.circe.generic.semiauto._
 
-  implicit val encoder: Encoder[{{classname}}] = deriveEncoder
+  implicit val encoder: Encoder[{{classname}}] = deriveEncoder[{{classname}}].mapJson(_.dropNullValues)
   implicit val decoder: Decoder[{{classname}}] = deriveDecoder
 {{/vendorExtensions.x-use-discr}}
 {{#vendorExtensions.x-use-discr}}
@@ -198,7 +198,7 @@ object {{classname}} {
         case other => sys.error(s"Invalid {{classname}} discriminant: ${other}")
       }
     )  
-  implicit val encoder: Encoder[{{classname}}] = deriveConfiguredEncoder
+  implicit val encoder: Encoder[{{classname}}] = deriveConfiguredEncoder[{{classname}}].mapJson(_.dropNullValues)
   implicit val decoder: Decoder[{{classname}}] = deriveConfiguredDecoder
 {{/vendorExtensions.x-use-discr}}
 {{/vendorExtensions.x-hasWrappedOneOfMembers}}
@@ -326,7 +326,7 @@ object {{classname}} {
   import io.circe.syntax._
   import io.circe.generic.semiauto._
 
-  implicit val encoder: Encoder[{{classname}}] = deriveEncoder
+  implicit val encoder: Encoder[{{classname}}] = deriveEncoder[{{classname}}].mapJson(_.dropNullValues)
   implicit val decoder: Decoder[{{classname}}] = deriveDecoder
 }
 {{/circe}}

modules/openapi-generator/src/test/java/org/openapitools/codegen/scala/Sttp4CodegenTest.java

@@ -333,4 +333,37 @@ public void verifyDateTimeLocalGeneratesLocalDateTime() throws IOException {
         assertFileContains(modelPath, "createdAt: OffsetDateTime");
         assertFileContains(modelPath, "updatedAt: Option[OffsetDateTime]");
     }
+
+    @Test
+    public void verifyOptionalFieldsOmittedWhenNone() throws IOException {
+        File output = Files.createTempDirectory("test").toFile().getCanonicalFile();
+        output.deleteOnExit();
+        String outputPath = output.getAbsolutePath().replace('\\', '/');
+
+        OpenAPI openAPI = new OpenAPIParser()
+                .readLocation("src/test/resources/3_0/scala/sttp4-optional-fields.yaml", null, new ParseOptions()).getOpenAPI();
+
+        ScalaSttp4ClientCodegen codegen = new ScalaSttp4ClientCodegen();
+        codegen.setOutputDir(output.getAbsolutePath());
+        codegen.additionalProperties().put("jsonLibrary", "circe");
+
+        ClientOptInput input = new ClientOptInput();
+        input.openAPI(openAPI);
+        input.config(codegen);
+
+        DefaultGenerator generator = new DefaultGenerator();
+
+        generator.setGeneratorPropertyDefault(CodegenConstants.MODELS, "true");
+        generator.setGeneratorPropertyDefault(CodegenConstants.MODEL_TESTS, "false");
+        generator.setGeneratorPropertyDefault(CodegenConstants.MODEL_DOCS, "false");
+        generator.setGeneratorPropertyDefault(CodegenConstants.APIS, "false");
+        generator.setGeneratorPropertyDefault(CodegenConstants.SUPPORTING_FILES, "false");
+        generator.opts(input).generate();
+
+        // Optional fields set to None must be omitted from the JSON (sttp3 parity),
+        // not serialized as null: strict servers reject explicit null for
+        // non-nullable optional properties.
+        Path petPath = Paths.get(outputPath + "/src/main/scala/org/openapitools/client/model/Pet.scala");
+        assertFileContains(petPath, "implicit val encoder: Encoder[Pet] = deriveEncoder[Pet].mapJson(_.dropNullValues)");
+    }
 }

modules/openapi-generator/src/test/resources/3_0/scala/sttp4-optional-fields.yaml

@@ -0,0 +1,32 @@
+openapi: 3.0.3
+info:
+  title: Optional field test
+  version: 1.0.0
+paths:
+  /pets:
+    post:
+      operationId: createPet
+      requestBody:
+        required: true
+        content:
+          application/json:
+            schema:
+              $ref: '#/components/schemas/Pet'
+      responses:
+        '200':
+          description: OK
+          content:
+            application/json:
+              schema:
+                $ref: '#/components/schemas/Pet'
+components:
+  schemas:
+    Pet:
+      type: object
+      required:
+        - name
+      properties:
+        name:
+          type: string
+        tag:
+          type: string

samples/client/petstore/scala-sttp4-circe/src/main/scala/org/openapitools/client/model/ApiResponse.scala

@@ -26,6 +26,6 @@ object ApiResponse {
   import io.circe.syntax._
   import io.circe.generic.semiauto._
 
-  implicit val encoder: Encoder[ApiResponse] = deriveEncoder
+  implicit val encoder: Encoder[ApiResponse] = deriveEncoder[ApiResponse].mapJson(_.dropNullValues)
   implicit val decoder: Decoder[ApiResponse] = deriveDecoder
 }

samples/client/petstore/scala-sttp4-circe/src/main/scala/org/openapitools/client/model/Category.scala

@@ -25,6 +25,6 @@ object Category {
   import io.circe.syntax._
   import io.circe.generic.semiauto._
 
-  implicit val encoder: Encoder[Category] = deriveEncoder
+  implicit val encoder: Encoder[Category] = deriveEncoder[Category].mapJson(_.dropNullValues)
   implicit val decoder: Decoder[Category] = deriveDecoder
 }

samples/client/petstore/scala-sttp4-circe/src/main/scala/org/openapitools/client/model/Order.scala

@@ -31,7 +31,7 @@ object Order {
   import io.circe.syntax._
   import io.circe.generic.semiauto._
 
-  implicit val encoder: Encoder[Order] = deriveEncoder
+  implicit val encoder: Encoder[Order] = deriveEncoder[Order].mapJson(_.dropNullValues)
   implicit val decoder: Decoder[Order] = deriveDecoder
 }
 object OrderEnums {

samples/client/petstore/scala-sttp4-circe/src/main/scala/org/openapitools/client/model/Pet.scala

@@ -30,7 +30,7 @@ object Pet {
   import io.circe.syntax._
   import io.circe.generic.semiauto._
 
-  implicit val encoder: Encoder[Pet] = deriveEncoder
+  implicit val encoder: Encoder[Pet] = deriveEncoder[Pet].mapJson(_.dropNullValues)
   implicit val decoder: Decoder[Pet] = deriveDecoder
 }
 object PetEnums {

samples/client/petstore/scala-sttp4-circe/src/main/scala/org/openapitools/client/model/Tag.scala

@@ -25,6 +25,6 @@ object Tag {
   import io.circe.syntax._
   import io.circe.generic.semiauto._
 
-  implicit val encoder: Encoder[Tag] = deriveEncoder
+  implicit val encoder: Encoder[Tag] = deriveEncoder[Tag].mapJson(_.dropNullValues)
   implicit val decoder: Decoder[Tag] = deriveDecoder
 }

samples/client/petstore/scala-sttp4-circe/src/main/scala/org/openapitools/client/model/User.scala

@@ -32,6 +32,6 @@ object User {
   import io.circe.syntax._
   import io.circe.generic.semiauto._
 
-  implicit val encoder: Encoder[User] = deriveEncoder
+  implicit val encoder: Encoder[User] = deriveEncoder[User].mapJson(_.dropNullValues)
   implicit val decoder: Decoder[User] = deriveDecoder
 }