fix: use oneOf mapping to map discriminator values to types

Author: plaflamme

modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/ScalaSttp4ClientCodegen.java

@@ -279,10 +279,27 @@ public Map<String, ModelsMap> postProcessAllModels(Map<String, ModelsMap> objs)
                             childModel.getVendorExtensions().put("x-isOneOfMember", true);
                             childModel.getVendorExtensions().put("x-oneOfParent", cModel.classname);
 
-                            // Remove discriminator field from child if parent has discriminator
-                            // (circe-generic-extras adds it automatically)
+                            // Add discriminator mapping value if present
                             if (cModel.discriminator != null) {
                                 String discriminatorName = cModel.discriminator.getPropertyName();
+                                
+                                // Find the mapping value for this child model
+                                String discriminatorValue = null;
+                                if (cModel.discriminator.getMappedModels() != null) {
+                                    for (CodegenDiscriminator.MappedModel mappedModel : cModel.discriminator.getMappedModels()) {
+                                        if (mappedModel.getModelName().equals(childName)) {
+                                            discriminatorValue = mappedModel.getMappingName();
+                                            break;
+                                        }
+                                    }
+                                }
+                                
+                                if (discriminatorValue != null) {
+                                    childModel.getVendorExtensions().put("x-discriminator-value", discriminatorValue);
+                                }
+                                
+                                // Remove discriminator field from child
+                                // (circe-generic-extras adds it automatically)
                                 childModel.vars.removeIf(prop -> prop.baseName.equals(discriminatorName));
                                 childModel.allVars.removeIf(prop -> prop.baseName.equals(discriminatorName));
                                 childModel.requiredVars.removeIf(prop -> prop.baseName.equals(discriminatorName));

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

@@ -103,7 +103,13 @@ object {{classname}} {
   import io.circe.generic.auto._
 
   private implicit val config: Configuration = Configuration.default.withDiscriminator("{{discriminator.propertyName}}")
-  
+    .copy(
+      transformConstructorNames = {
+{{#vendorExtensions.x-oneOfMembers}}
+        case "{{classname}}" => "{{vendorExtensions.x-discriminator-value}}"
+{{/vendorExtensions.x-oneOfMembers}}
+      }
+    )  
   implicit val encoder: Encoder[{{classname}}] = deriveConfiguredEncoder
   implicit val decoder: Decoder[{{classname}}] = deriveConfiguredDecoder
 {{/vendorExtensions.x-use-discr}}