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[java] fix: okhttp-gson additionalProperties field makes every allOf child undeserializable #24895

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[java] fix: okhttp-gson additionalProperties field makes every allOf child undeserializable #24895

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eb98f3c
[java] fix: the okhttp-gson additionalProperties bag breaks every all…
wiebren Sep 8, 2026
20b5c48
[java] fix: keep the bag visible on parents that have no adapter of t…
wiebren Sep 8, 2026
2b160d6
[java] docs: describe gson's field binding accurately
wiebren Sep 9, 2026
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9 changes: 8 additions & 1 deletion ...pi-generator/src/main/resources/Java/libraries/okhttp-gson/additional_properties.mustache
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Original file line number Diff line number Diff line change
Expand Up @@ -3,8 +3,15 @@
* A container for additional, undeclared properties.
* This is a holder for any undeclared properties as specified with
* the 'additionalProperties' keyword in the OAS document.
*
* Transient (on models without children): the bag is read and written by this model's
* TypeAdapterFactory, so gson's reflection does not need to see it. Gson collects the
* declared fields of every class in the hierarchy and rejects two bound to one JSON
* name, which is what an allOf child - declaring the field itself and inheriting it -
* used to hit. A parent with children has no factory of its own, so it keeps the field
* bound for reflection; the child excludes only its own copy, leaving exactly one.

@cubic-dev-ai cubic-dev-ai Bot Sep 9, 2026

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P1: With a three-level allOf inheritance chain, the leaf still encounters duplicate additionalProperties fields: every ancestor with children remains non-transient, while only the leaf is hidden. Hide all but one field per inheritance hierarchy and add a multi-level regression test.

Prompt for AI agents 
Check if this issue is valid — if so, understand the root cause and fix it. At modules/openapi-generator/src/main/resources/Java/libraries/okhttp-gson/additional_properties.mustache, line 12:

<comment>With a three-level `allOf` inheritance chain, the leaf still encounters duplicate `additionalProperties` fields: every ancestor with children remains non-transient, while only the leaf is hidden. Hide all but one field per inheritance hierarchy and add a multi-level regression test.</comment>

<file context>
@@ -5,10 +5,11 @@
+   * declared fields of every class in the hierarchy and rejects two bound to one JSON
+   * name, which is what an allOf child - declaring the field itself and inheriting it -
+   * used to hit. A parent with children has no factory of its own, so it keeps the field
+   * bound for reflection; the child excludes only its own copy, leaving exactly one.
    */
   private {{^hasChildren}}transient {{/hasChildren}}Map<String, Object> additionalProperties;
</file context>

*/
private Map<String, Object> additionalProperties;
private {{^hasChildren}}transient {{/hasChildren}}Map<String, Object> additionalProperties;

/**
* Set the additional (undeclared) property with the specified name and value.
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35 changes: 35 additions & 0 deletions .../openapi-generator/src/test/java/org/openapitools/codegen/java/JavaClientCodegenTest.java
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Original file line number Diff line number Diff line change
Expand Up @@ -2024,6 +2024,41 @@ public void testJdkHttpClientWithAndWithoutParentExtension() {
.content().contains("public class AnotherChild {");
}

@Test
public void testAdditionalPropertiesFieldIsTransientForGson() {
final Path output = newTempFolder();
final CodegenConfigurator configurator = new CodegenConfigurator()
.setGeneratorName(JAVA_GENERATOR)
// use default `okhttp-gson`
.addAdditionalProperty(CodegenConstants.API_PACKAGE, "xyz.abcdef.api")
.addAdditionalProperty(CodegenConstants.MODEL_PACKAGE, "xyz.abcdef.model")
.addAdditionalProperty(CodegenConstants.INVOKER_PACKAGE, "xyz.abcdef.invoker")
.addAdditionalProperty("disallowAdditionalPropertiesIfNotPresent", "false")
.setInputSpec("src/test/resources/3_0/allOf_extension_parent.yaml")
.setOutputDir(output.toString().replace("\\", "/"));

DefaultGenerator generator = new DefaultGenerator();
generator.setGeneratorPropertyDefault(CodegenConstants.MODELS, "true");
generator.opts(configurator.toClientOptInput()).generate();

// gson's reflective adapter refuses a class with two JSON fields of one name; without
// `transient` an allOf child declares additionalProperties itself and inherits it too,
// making it undeserializable ("declares multiple JSON fields named
// 'additionalProperties'"). The child's bag is read and written by its own
// TypeAdapterFactory, so hiding the field from reflection changes nothing else.
assertThat(output.resolve("src/main/java/xyz/abcdef/model/Child.java"))
.content()
.contains("public class Child extends Person {")
.contains("private transient Map<String, Object> additionalProperties;");
// a parent with children gets no TypeAdapterFactory of its own ({{^hasChildren}} in
// pojo.mustache), so its field stays visible to reflection - the child's transient
// declaration shadows it, and no duplicate JSON field arises
assertThat(output.resolve("src/main/java/xyz/abcdef/model/Person.java"))
.content().contains("private Map<String, Object> additionalProperties;");
assertThat(output.resolve("src/main/java/xyz/abcdef/model/Person.java"))
.content().doesNotContain("private transient Map<String, Object> additionalProperties;");
}

@Test
public void allOfWithSeveralRefsAndRefAsParentInAllOfNormalizationIsTrue() {
final Path output = newTempFolder();
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9 changes: 8 additions & 1 deletion ...re/java/okhttp-gson-3.1/src/main/java/org/openapitools/client/model/AllOfSimpleModel.java
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Expand Up @@ -91,8 +91,15 @@ public void setArrayOfStrings(@javax.annotation.Nonnull List<String> arrayOfStri
* A container for additional, undeclared properties.
* This is a holder for any undeclared properties as specified with
* the 'additionalProperties' keyword in the OAS document.
*
* Transient (on models without children): the bag is read and written by this model's
* TypeAdapterFactory, so gson's reflection does not need to see it. Gson collects the
* declared fields of every class in the hierarchy and rejects two bound to one JSON
* name, which is what an allOf child - declaring the field itself and inheriting it -
* used to hit. A parent with children has no factory of its own, so it keeps the field
* bound for reflection; the child excludes only its own copy, leaving exactly one.
*/
private Map<String, Object> additionalProperties;
private transient Map<String, Object> additionalProperties;

/**
* Set the additional (undeclared) property with the specified name and value.
Expand Down
7 changes: 7 additions & 0 deletions ...ent/petstore/java/okhttp-gson-3.1/src/main/java/org/openapitools/client/model/Animal.java
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Expand Up @@ -106,6 +106,13 @@ public void setColor(@javax.annotation.Nullable String color) {
* A container for additional, undeclared properties.
* This is a holder for any undeclared properties as specified with
* the 'additionalProperties' keyword in the OAS document.
*
* Transient (on models without children): the bag is read and written by this model's
* TypeAdapterFactory, so gson's reflection does not need to see it. Gson collects the
* declared fields of every class in the hierarchy and rejects two bound to one JSON
* name, which is what an allOf child - declaring the field itself and inheriting it -
* used to hit. A parent with children has no factory of its own, so it keeps the field
* bound for reflection; the child excludes only its own copy, leaving exactly one.
*/
private Map<String, Object> additionalProperties;

Expand Down
9 changes: 8 additions & 1 deletion ...etstore/java/okhttp-gson-3.1/src/main/java/org/openapitools/client/model/AnyTypeTest.java
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Expand Up @@ -148,8 +148,15 @@ public void setRefArrayPrefixItems(@javax.annotation.Nullable List<Object> refAr
* A container for additional, undeclared properties.
* This is a holder for any undeclared properties as specified with
* the 'additionalProperties' keyword in the OAS document.
*
* Transient (on models without children): the bag is read and written by this model's
* TypeAdapterFactory, so gson's reflection does not need to see it. Gson collects the
* declared fields of every class in the hierarchy and rejects two bound to one JSON
* name, which is what an allOf child - declaring the field itself and inheriting it -
* used to hit. A parent with children has no factory of its own, so it keeps the field
* bound for reflection; the child excludes only its own copy, leaving exactly one.
*/
private Map<String, Object> additionalProperties;
private transient Map<String, Object> additionalProperties;

/**
* Set the additional (undeclared) property with the specified name and value.
Expand Down
9 changes: 8 additions & 1 deletion ...tore/java/okhttp-gson-3.1/src/main/java/org/openapitools/client/model/ArrayOfSameRef.java
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Expand Up @@ -156,8 +156,15 @@ public void setArrayFooThree(@javax.annotation.Nullable List<Tag> arrayFooThree)
* A container for additional, undeclared properties.
* This is a holder for any undeclared properties as specified with
* the 'additionalProperties' keyword in the OAS document.
*
* Transient (on models without children): the bag is read and written by this model's
* TypeAdapterFactory, so gson's reflection does not need to see it. Gson collects the
* declared fields of every class in the hierarchy and rejects two bound to one JSON
* name, which is what an allOf child - declaring the field itself and inheriting it -
* used to hit. A parent with children has no factory of its own, so it keeps the field
* bound for reflection; the child excludes only its own copy, leaving exactly one.
*/
private Map<String, Object> additionalProperties;
private transient Map<String, Object> additionalProperties;

/**
* Set the additional (undeclared) property with the specified name and value.
Expand Down
9 changes: 8 additions & 1 deletion ...client/petstore/java/okhttp-gson-3.1/src/main/java/org/openapitools/client/model/Cat.java
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Expand Up @@ -83,8 +83,15 @@ public void setDeclawed(@javax.annotation.Nullable Boolean declawed) {
* A container for additional, undeclared properties.
* This is a holder for any undeclared properties as specified with
* the 'additionalProperties' keyword in the OAS document.
*
* Transient (on models without children): the bag is read and written by this model's
* TypeAdapterFactory, so gson's reflection does not need to see it. Gson collects the
* declared fields of every class in the hierarchy and rejects two bound to one JSON
* name, which is what an allOf child - declaring the field itself and inheriting it -
* used to hit. A parent with children has no factory of its own, so it keeps the field
* bound for reflection; the child excludes only its own copy, leaving exactly one.
*/
private Map<String, Object> additionalProperties;
private transient Map<String, Object> additionalProperties;

/**
* Set the additional (undeclared) property with the specified name and value.
Expand Down
9 changes: 8 additions & 1 deletion ...t/petstore/java/okhttp-gson-3.1/src/main/java/org/openapitools/client/model/Category.java
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Expand Up @@ -105,8 +105,15 @@ public void setName(@javax.annotation.Nullable String name) {
* A container for additional, undeclared properties.
* This is a holder for any undeclared properties as specified with
* the 'additionalProperties' keyword in the OAS document.
*
* Transient (on models without children): the bag is read and written by this model's
* TypeAdapterFactory, so gson's reflection does not need to see it. Gson collects the
* declared fields of every class in the hierarchy and rejects two bound to one JSON
* name, which is what an allOf child - declaring the field itself and inheriting it -
* used to hit. A parent with children has no factory of its own, so it keeps the field
* bound for reflection; the child excludes only its own copy, leaving exactly one.
*/
private Map<String, Object> additionalProperties;
private transient Map<String, Object> additionalProperties;

/**
* Set the additional (undeclared) property with the specified name and value.
Expand Down
9 changes: 8 additions & 1 deletion .../java/okhttp-gson-3.1/src/main/java/org/openapitools/client/model/CircularReference1.java
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Expand Up @@ -82,8 +82,15 @@ public void setProp1(@javax.annotation.Nullable CircularReference2 prop1) {
* A container for additional, undeclared properties.
* This is a holder for any undeclared properties as specified with
* the 'additionalProperties' keyword in the OAS document.
*
* Transient (on models without children): the bag is read and written by this model's
* TypeAdapterFactory, so gson's reflection does not need to see it. Gson collects the
* declared fields of every class in the hierarchy and rejects two bound to one JSON
* name, which is what an allOf child - declaring the field itself and inheriting it -
* used to hit. A parent with children has no factory of its own, so it keeps the field
* bound for reflection; the child excludes only its own copy, leaving exactly one.
*/
private Map<String, Object> additionalProperties;
private transient Map<String, Object> additionalProperties;

/**
* Set the additional (undeclared) property with the specified name and value.
Expand Down
9 changes: 8 additions & 1 deletion .../java/okhttp-gson-3.1/src/main/java/org/openapitools/client/model/CircularReference2.java
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Expand Up @@ -82,8 +82,15 @@ public void setProp1(@javax.annotation.Nullable CircularReference3 prop1) {
* A container for additional, undeclared properties.
* This is a holder for any undeclared properties as specified with
* the 'additionalProperties' keyword in the OAS document.
*
* Transient (on models without children): the bag is read and written by this model's
* TypeAdapterFactory, so gson's reflection does not need to see it. Gson collects the
* declared fields of every class in the hierarchy and rejects two bound to one JSON
* name, which is what an allOf child - declaring the field itself and inheriting it -
* used to hit. A parent with children has no factory of its own, so it keeps the field
* bound for reflection; the child excludes only its own copy, leaving exactly one.
*/
private Map<String, Object> additionalProperties;
private transient Map<String, Object> additionalProperties;

/**
* Set the additional (undeclared) property with the specified name and value.
Expand Down
9 changes: 8 additions & 1 deletion .../java/okhttp-gson-3.1/src/main/java/org/openapitools/client/model/CircularReference3.java
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Expand Up @@ -82,8 +82,15 @@ public void setProp1(@javax.annotation.Nullable CircularReference1 prop1) {
* A container for additional, undeclared properties.
* This is a holder for any undeclared properties as specified with
* the 'additionalProperties' keyword in the OAS document.
*
* Transient (on models without children): the bag is read and written by this model's
* TypeAdapterFactory, so gson's reflection does not need to see it. Gson collects the
* declared fields of every class in the hierarchy and rejects two bound to one JSON
* name, which is what an allOf child - declaring the field itself and inheriting it -
* used to hit. A parent with children has no factory of its own, so it keeps the field
* bound for reflection; the child excludes only its own copy, leaving exactly one.
*/
private Map<String, Object> additionalProperties;
private transient Map<String, Object> additionalProperties;

/**
* Set the additional (undeclared) property with the specified name and value.
Expand Down
9 changes: 8 additions & 1 deletion ...client/petstore/java/okhttp-gson-3.1/src/main/java/org/openapitools/client/model/Dog.java
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Expand Up @@ -83,8 +83,15 @@ public void setBreed(@javax.annotation.Nullable String breed) {
* A container for additional, undeclared properties.
* This is a holder for any undeclared properties as specified with
* the 'additionalProperties' keyword in the OAS document.
*
* Transient (on models without children): the bag is read and written by this model's
* TypeAdapterFactory, so gson's reflection does not need to see it. Gson collects the
* declared fields of every class in the hierarchy and rejects two bound to one JSON
* name, which is what an allOf child - declaring the field itself and inheriting it -
* used to hit. A parent with children has no factory of its own, so it keeps the field
* bound for reflection; the child excludes only its own copy, leaving exactly one.
*/
private Map<String, Object> additionalProperties;
private transient Map<String, Object> additionalProperties;

/**
* Set the additional (undeclared) property with the specified name and value.
Expand Down
9 changes: 8 additions & 1 deletion ....1/src/main/java/org/openapitools/client/model/FakeWebhooksSourcesDeletedPostRequest.java
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Expand Up @@ -131,8 +131,15 @@ public void setEvent(@javax.annotation.Nonnull FakeWebhooksSourcesDeletedPostReq
* A container for additional, undeclared properties.
* This is a holder for any undeclared properties as specified with
* the 'additionalProperties' keyword in the OAS document.
*
* Transient (on models without children): the bag is read and written by this model's
* TypeAdapterFactory, so gson's reflection does not need to see it. Gson collects the
* declared fields of every class in the hierarchy and rejects two bound to one JSON
* name, which is what an allOf child - declaring the field itself and inheriting it -
* used to hit. A parent with children has no factory of its own, so it keeps the field
* bound for reflection; the child excludes only its own copy, leaving exactly one.
*/
private Map<String, Object> additionalProperties;
private transient Map<String, Object> additionalProperties;

/**
* Set the additional (undeclared) property with the specified name and value.
Expand Down
9 changes: 8 additions & 1 deletion ...c/main/java/org/openapitools/client/model/FakeWebhooksSourcesDeletedPostRequestEvent.java
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Expand Up @@ -81,8 +81,15 @@ public void setEventId(@javax.annotation.Nonnull String eventId) {
* A container for additional, undeclared properties.
* This is a holder for any undeclared properties as specified with
* the 'additionalProperties' keyword in the OAS document.
*
* Transient (on models without children): the bag is read and written by this model's
* TypeAdapterFactory, so gson's reflection does not need to see it. Gson collects the
* declared fields of every class in the hierarchy and rejects two bound to one JSON
* name, which is what an allOf child - declaring the field itself and inheriting it -
* used to hit. A parent with children has no factory of its own, so it keeps the field
* bound for reflection; the child excludes only its own copy, leaving exactly one.
*/
private Map<String, Object> additionalProperties;
private transient Map<String, Object> additionalProperties;

/**
* Set the additional (undeclared) property with the specified name and value.
Expand Down
9 changes: 8 additions & 1 deletion ...re/java/okhttp-gson-3.1/src/main/java/org/openapitools/client/model/ModelApiResponse.java
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Expand Up @@ -129,8 +129,15 @@ public void setMessage(@javax.annotation.Nullable String message) {
* A container for additional, undeclared properties.
* This is a holder for any undeclared properties as specified with
* the 'additionalProperties' keyword in the OAS document.
*
* Transient (on models without children): the bag is read and written by this model's
* TypeAdapterFactory, so gson's reflection does not need to see it. Gson collects the
* declared fields of every class in the hierarchy and rejects two bound to one JSON
* name, which is what an allOf child - declaring the field itself and inheriting it -
* used to hit. A parent with children has no factory of its own, so it keeps the field
* bound for reflection; the child excludes only its own copy, leaving exactly one.
*/
private Map<String, Object> additionalProperties;
private transient Map<String, Object> additionalProperties;

/**
* Set the additional (undeclared) property with the specified name and value.
Expand Down
9 changes: 8 additions & 1 deletion ...ient/petstore/java/okhttp-gson-3.1/src/main/java/org/openapitools/client/model/Order.java
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Expand Up @@ -256,8 +256,15 @@ public void setComplete(@javax.annotation.Nullable Boolean complete) {
* A container for additional, undeclared properties.
* This is a holder for any undeclared properties as specified with
* the 'additionalProperties' keyword in the OAS document.
*
* Transient (on models without children): the bag is read and written by this model's
* TypeAdapterFactory, so gson's reflection does not need to see it. Gson collects the
* declared fields of every class in the hierarchy and rejects two bound to one JSON
* name, which is what an allOf child - declaring the field itself and inheriting it -
* used to hit. A parent with children has no factory of its own, so it keeps the field
* bound for reflection; the child excludes only its own copy, leaving exactly one.
*/
private Map<String, Object> additionalProperties;
private transient Map<String, Object> additionalProperties;

/**
* Set the additional (undeclared) property with the specified name and value.
Expand Down
9 changes: 8 additions & 1 deletion ...client/petstore/java/okhttp-gson-3.1/src/main/java/org/openapitools/client/model/Pet.java
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Expand Up @@ -280,8 +280,15 @@ public void setStatus(@javax.annotation.Nullable StatusEnum status) {
* A container for additional, undeclared properties.
* This is a holder for any undeclared properties as specified with
* the 'additionalProperties' keyword in the OAS document.
*
* Transient (on models without children): the bag is read and written by this model's
* TypeAdapterFactory, so gson's reflection does not need to see it. Gson collects the
* declared fields of every class in the hierarchy and rejects two bound to one JSON
* name, which is what an allOf child - declaring the field itself and inheriting it -
* used to hit. A parent with children has no factory of its own, so it keeps the field
* bound for reflection; the child excludes only its own copy, leaving exactly one.
*/
private Map<String, Object> additionalProperties;
private transient Map<String, Object> additionalProperties;

/**
* Set the additional (undeclared) property with the specified name and value.
Expand Down
9 changes: 8 additions & 1 deletion ...tp-gson-3.1/src/main/java/org/openapitools/client/model/PetWithTypesObjectNullAndRef.java
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Expand Up @@ -107,8 +107,15 @@ public void setSecondProperty(@javax.annotation.Nullable Object secondProperty)
* A container for additional, undeclared properties.
* This is a holder for any undeclared properties as specified with
* the 'additionalProperties' keyword in the OAS document.
*
* Transient (on models without children): the bag is read and written by this model's
* TypeAdapterFactory, so gson's reflection does not need to see it. Gson collects the
* declared fields of every class in the hierarchy and rejects two bound to one JSON
* name, which is what an allOf child - declaring the field itself and inheriting it -
* used to hit. A parent with children has no factory of its own, so it keeps the field
* bound for reflection; the child excludes only its own copy, leaving exactly one.
*/
private Map<String, Object> additionalProperties;
private transient Map<String, Object> additionalProperties;

/**
* Set the additional (undeclared) property with the specified name and value.
Expand Down
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