Discard mapped dmodels with matching explicit discriminator mappings (#20939)

Author: TheMrMilchmann

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

@@ -3682,7 +3682,8 @@ protected CodegenDiscriminator createDiscriminator(String schemaName, Schema sch
         if (ModelUtils.isComposedSchema(schema) && !this.getLegacyDiscriminatorBehavior()) {
             List<MappedModel> otherDescendants = getOneOfAnyOfDescendants(schemaName, discriminatorPropertyName, schema);
             for (MappedModel otherDescendant : otherDescendants) {
-                if (!uniqueDescendants.contains(otherDescendant)) {
+                // add only if the model names are not the same
+                if (uniqueDescendants.stream().map(MappedModel::getModelName).noneMatch(it -> it.equals(otherDescendant.getModelName()))) {
                     uniqueDescendants.add(otherDescendant);
                 }
             }

samples/client/others/go/oneof-discriminator-lookup/model_object.go

@@ -30,9 +30,7 @@
 @JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.PROPERTY, property = "fruitType", visible = true)
 @JsonSubTypes({
   @JsonSubTypes.Type(value = Apple.class, name = "APPLE"),
-  @JsonSubTypes.Type(value = Banana.class, name = "BANANA"),
-  @JsonSubTypes.Type(value = Apple.class, name = "Apple"),
-  @JsonSubTypes.Type(value = Banana.class, name = "Banana")
+  @JsonSubTypes.Type(value = Banana.class, name = "BANANA")
 })
 
 @Generated(value = "org.openapitools.codegen.languages.SpringCodegen", comments = "Generator version: 7.15.0-SNAPSHOT")