fix: [java] okhttp-gson allOf children of a oneOf/anyOf parent do not compile with additionalProperties (#25156)

With disallowAdditionalPropertiesIfNotPresent=false, an allOf child of a
discriminated oneOf/anyOf parent was tagged x-inherits-additional-properties
because the parent model has isAdditionalPropertiesTrue. The parent is
rendered by oneof_model/anyof_model, which extends AbstractOpenApiSchema
and declares no bag, so the child's @OverRide putAdditionalProperty and
its super calls had nothing to bind to.

Stop the ancestor walk at a oneOf/anyOf model: nothing is inherited
through it, so the first pojo below it declares the bag again.

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

Author: wiebren

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

@@ -1243,9 +1243,14 @@ public Map<String, ModelsMap> postProcessAllModels(Map<String, ModelsMap> objs)
         if (isLibrary(OKHTTP_GSON)) {
             // gson refuses a class whose hierarchy declares two fields bound to one JSON name, so
             // the okhttp-gson additionalProperties bag is declared once, on the topmost ancestor
-            // that has one; every descendant inherits it instead of declaring its own copy
+            // that has one; every descendant inherits it instead of declaring its own copy.
+            // A oneOf/anyOf wrapper extends AbstractOpenApiSchema, not its own parent, and has no
+            // bag, so nothing is inherited through it
             for (CodegenModel cm : getAllModels(objs).values()) {
                 for (CodegenModel ancestor = cm.getParentModel(); ancestor != null; ancestor = ancestor.getParentModel()) {
+                    if (!ancestor.oneOf.isEmpty() || !ancestor.anyOf.isEmpty()) {
+                        break;
+                    }
                     if (ancestor.isAdditionalPropertiesTrue) {
                         cm.vendorExtensions.put("x-inherits-additional-properties", true);
                         break;

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

@@ -2263,6 +2263,31 @@ public void testAdditionalPropertiesFieldIsDeclaredOnceAcrossMultiLevelAllOfForG
                 .doesNotContain("Map<String, Object> additionalProperties;");
     }
 
+    @Test
+    public void testAdditionalPropertiesFieldIsDeclaredBelowOneOfAndAnyOfParentsForGson() {
+        final Path output = generateOkHttpGsonWithAdditionalProperties("src/test/resources/3_0/java/okhttp-gson-additional-properties-composed-parent.yaml");
+
+        // a oneOf/anyOf wrapper has no bag to inherit, so its allOf children declare their own
+        assertThat(output.resolve("src/main/java/xyz/abcdef/model/Pet.java"))
+                .content()
+                .contains("public class Pet extends AbstractOpenApiSchema")
+                .doesNotContain("Map<String, Object> additionalProperties;");
+        assertThat(output.resolve("src/main/java/xyz/abcdef/model/ExtendedPet.java"))
+                .content()
+                .contains("public class ExtendedPet extends Pet {")
+                .contains("private Map<String, Object> additionalProperties;");
+        assertThat(output.resolve("src/main/java/xyz/abcdef/model/ExtendedShape.java"))
+                .content()
+                .contains("public class ExtendedShape extends Shape {")
+                .contains("private Map<String, Object> additionalProperties;");
+        // below the first class that declares it, the bag is inherited as usual
+        assertThat(output.resolve("src/main/java/xyz/abcdef/model/ExtendedPetLeaf.java"))
+                .content()
+                .contains("public class ExtendedPetLeaf extends ExtendedPet {")
+                .contains("public ExtendedPetLeaf putAdditionalProperty(String key, Object value) {")
+                .doesNotContain("Map<String, Object> additionalProperties;");
+    }
+
     private Path generateOkHttpGsonWithAdditionalProperties(String inputSpec) {
         final Path output = newTempFolder();
         final CodegenConfigurator configurator = new CodegenConfigurator()

modules/openapi-generator/src/test/resources/3_0/java/okhttp-gson-additional-properties-composed-parent.yaml

@@ -0,0 +1,78 @@
+openapi: 3.0.3
+info: {title: t, version: '1'}
+paths:
+  /pet:
+    get:
+      responses:
+        '200':
+          description: ok
+          content:
+            application/json:
+              schema: {$ref: '#/components/schemas/ExtendedPetLeaf'}
+  /shape:
+    get:
+      responses:
+        '200':
+          description: ok
+          content:
+            application/json:
+              schema: {$ref: '#/components/schemas/ExtendedShape'}
+components:
+  schemas:
+    Cat:
+      type: object
+      required: [petType]
+      properties:
+        petType: {type: string}
+        meows: {type: boolean}
+    Dog:
+      type: object
+      required: [petType]
+      properties:
+        petType: {type: string}
+        barks: {type: boolean}
+    Pet:
+      oneOf:
+        - $ref: '#/components/schemas/Cat'
+        - $ref: '#/components/schemas/Dog'
+      discriminator: {propertyName: petType}
+    ExtendedPet:
+      allOf:
+        - $ref: '#/components/schemas/Pet'
+        - type: object
+          required: [petType]
+          properties:
+            petType: {type: string}
+            name: {type: string}
+      discriminator: {propertyName: petType}
+    ExtendedPetLeaf:
+      allOf:
+        - $ref: '#/components/schemas/ExtendedPet'
+        - type: object
+          properties:
+            nickname: {type: string}
+    Circle:
+      type: object
+      required: [shapeType]
+      properties:
+        shapeType: {type: string}
+        radius: {type: number}
+    Square:
+      type: object
+      required: [shapeType]
+      properties:
+        shapeType: {type: string}
+        side: {type: number}
+    Shape:
+      anyOf:
+        - $ref: '#/components/schemas/Circle'
+        - $ref: '#/components/schemas/Square'
+      discriminator: {propertyName: shapeType}
+    ExtendedShape:
+      allOf:
+        - $ref: '#/components/schemas/Shape'
+        - type: object
+          required: [shapeType]
+          properties:
+            shapeType: {type: string}
+            colour: {type: string}