[java][okhttp] Handle JSON-B parents without a discriminator

A model with children but no discriminator (x-parent, or a single allOf
$ref) got neither the leaf (de)serializers, which skip every model with
children, nor the hierarchy-root ones, which required a discriminator. It
fell back to plain bean mapping and lost its required-field checks and
additionalProperties. The root (de)serializers now cover every parent; with
no discriminator the deserializer binds the root itself. Subtypes still
delegate to the polymorphism-free instance, so Yasson's superclass lookup
cannot narrow them to the parent. No sample defines such a parent.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

Author: rar91279

modules/openapi-generator/src/main/resources/Java/libraries/okhttp/JSON.mustache

@@ -784,10 +784,8 @@ public class JSON {
         {{#model}}
         {{^isEnum}}
         {{#hasChildren}}
-        {{#discriminator}}
         config.withSerializers(new {{modelPackage}}.{{classname}}.CustomJsonbSerializer());
         config.withDeserializers(new {{modelPackage}}.{{classname}}.CustomJsonbDeserializer());
-        {{/discriminator}}
         {{/hasChildren}}
         {{/isEnum}}
         {{/model}}

modules/openapi-generator/src/main/resources/Java/libraries/okhttp/pojo.mustache

@@ -31,7 +31,6 @@ import jakarta.json.bind.adapter.JsonbAdapter;
 import jakarta.json.bind.annotation.JsonbTransient;
 import jakarta.json.bind.annotation.JsonbTypeAdapter;
 {{#hasChildren}}
-{{#discriminator}}
 import jakarta.json.JsonObject;
 import jakarta.json.bind.JsonbException;
 import jakarta.json.bind.serializer.DeserializationContext;
@@ -41,7 +40,6 @@ import jakarta.json.bind.serializer.SerializationContext;
 import jakarta.json.stream.JsonGenerator;
 import jakarta.json.stream.JsonParser;
 import java.lang.reflect.Type;
-{{/discriminator}}
 {{/hasChildren}}
 {{#isAdditionalPropertiesTrue}}
 {{^hasChildren}}
@@ -788,7 +786,10 @@ public class {{classname}} {{#parent}}extends {{{.}}} {{/parent}}{{#vendorExtens
 {{/isGson}}
 {{#isJsonb}}
 {{#hasChildren}}
-{{#discriminator}}
+{{! A parent without a discriminator (x-parent, or a single allOf $ref) needs these too: the
+    leaf (de)serializers below are skipped for every model with children, and Yasson falls
+    back to a superclass' serializer, so only this delegating variant is safe for a parent.
+    With no discriminator the deserializer simply binds the root itself. }}
 
   /**
    * Custom JSON-B serializer for the root of a discriminated hierarchy. Yasson serializes a
@@ -886,7 +887,9 @@ public class {{classname}} {{#parent}}extends {{{.}}} {{/parent}}{{#vendorExtens
     @Override
     public {{classname}} deserialize(JsonParser parser, DeserializationContext context, Type rtType) {
       JsonObject jsonObj = parser.getObject();
+      {{#discriminator}}
       String discriminatorValue = jsonObj.getString("{{{discriminator.propertyBaseName}}}", null);
+      {{/discriminator}}
       {{#discriminator.mappedModels}}
       if ("{{mappingName}}".equals(discriminatorValue)) {
         {{#model}}
@@ -960,7 +963,6 @@ public class {{classname}} {{#parent}}extends {{{.}}} {{/parent}}{{#vendorExtens
       }
     }
   }
-{{/discriminator}}
 {{/hasChildren}}
 {{#isAdditionalPropertiesTrue}}
 {{^hasChildren}}

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

@@ -5739,6 +5739,24 @@ public void testOkhttpJsonbEmitsPolymorphismSerializers() {
         assertThat(files.get("Cat.java")).content().doesNotContain("discriminatorValue");
     }
 
+    @Test(description = "a JSON-B parent without a discriminator (x-parent) gets the delegating root "
+            + "(de)serializers, since the leaf ones are skipped for every model with children")
+    public void testOkhttpJsonbParentWithoutDiscriminator() {
+        final Map<String, File> files = generateFromContract(
+                "src/test/resources/3_0/allOf_extension_parent.yaml",
+                JavaClientCodegen.OKHTTP,
+                Map.of(CodegenConstants.SERIALIZATION_LIBRARY, SERIALIZATION_LIBRARY_JSONB));
+
+        assertThat(files.get("Person.java")).content()
+                .contains("public static class CustomJsonbSerializer implements JsonbSerializer<Person>")
+                .contains("public static class CustomJsonbDeserializer implements JsonbDeserializer<Person>")
+                .contains("validateRequiredFields(jsonObj, openapiRequiredFields, \"Person\");")
+                .doesNotContain("discriminatorValue");
+        assertThat(files.get("JSON.java")).content()
+                .contains("config.withSerializers(new org.openapitools.client.model.Person.CustomJsonbSerializer());")
+                .contains("config.withDeserializers(new org.openapitools.client.model.Person.CustomJsonbDeserializer());");
+    }
+
     @Test(description = "okhttp Jackson models import Arrays and Map only when the template uses them")
     public void testOkhttpJacksonModelImportsArraysAndMapOnlyWhenUsed() {
         final Map<String, File> files = generateFromContract(