Fix allOf with $ref to discriminator-less oneOf flattening all variant properties

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

@@ -2802,18 +2802,31 @@ protected void updateModelForComposedSchema(CodegenModel m, Schema schema, Map<S
                 addImport(composed, refSchema, m, modelName);
 
                 if (allDefinitions != null && refSchema != null) {
+                    // When the refSchema is a oneOf wrapper, do not flatten the variant
+                    // properties into this model — that would produce an impossible
+                    // conjunction of all variants' properties. The wrapper's own
+                    // properties/required (shared fields declared on the wrapper itself)
+                    // should still be inherited. The oneOf variants are tracked via
+                    // m.interfaces. Pre-seeding visitedSchemas with the variant schemas
+                    // suppresses recursion into them inside addProperties().
+                    Set<Schema> visited = new HashSet<>();
+                    if (ModelUtils.hasOneOf(refSchema) && refSchema.getOneOf() != null) {
+                        for (Object variant : refSchema.getOneOf()) {
+                            visited.add((Schema) variant);
+                        }
+                    }
                     if (allParents.contains(ref) && supportsMultipleInheritance) {
                         // multiple inheritance
-                        addProperties(allProperties, allRequired, refSchema, new HashSet<>());
+                        addProperties(allProperties, allRequired, refSchema, visited);
                     } else if (parentName != null && parentName.equals(ref) && supportsInheritance) {
                         // single inheritance
-                        addProperties(allProperties, allRequired, refSchema, new HashSet<>());
+                        addProperties(allProperties, allRequired, refSchema, visited);
                     } else {
                         // composition
                         Map<String, Schema> newProperties = new LinkedHashMap<>();
-                        addProperties(newProperties, required, refSchema, new HashSet<>());
+                        addProperties(newProperties, required, refSchema, new HashSet<>(visited));
                         mergeProperties(properties, newProperties);
-                        addProperties(allProperties, allRequired, refSchema, new HashSet<>());
+                        addProperties(allProperties, allRequired, refSchema, visited);
                     }
                 }
 

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

@@ -707,6 +707,13 @@ private boolean modelIsMutable(CodegenModel model, Set<String> processed) {
             processed = new HashSet<String>();
         }
         boolean isMutable = model.allVars.stream().anyMatch(v -> !v.isReadOnly);
+        // oneOf/anyOf union wrappers expose a constructor per variant; the variants
+        // are not tracked in allVars, so fall back to the composed schema lists.
+        if (!isMutable && model.getComposedSchemas() != null) {
+            List<CodegenProperty> oneOf = model.getComposedSchemas().getOneOf();
+            List<CodegenProperty> anyOf = model.getComposedSchemas().getAnyOf();
+            isMutable = (oneOf != null && !oneOf.isEmpty()) || (anyOf != null && !anyOf.isEmpty());
+        }
         if (!isMutable && !processed.contains(model.classname) && model.getDiscriminator() != null && model.getDiscriminator().getMappedModels() != null) {
             processed.add(model.classname);
             isMutable = modelIsMutable(model, processed);

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

@@ -1589,6 +1589,11 @@ public static String getParentName(Schema composedSchema, Map<String, Schema> al
                     } else if (hasOrInheritsDiscriminator(s, allSchemas, new ArrayList<Schema>())) {
                         // discriminator.propertyName is used or x-parent is used
                         parentNameCandidates.add(parentName);
+                    } else if (hasOneOf(s)) {
+                        // a $ref to a oneOf schema is treated as a parent even without
+                        // a discriminator, to avoid flattening union type variants into
+                        // an impossible conjunction of all variant properties
+                        parentNameCandidates.add(parentName);
                     } else {
                         // not a parent since discriminator.propertyName or x-parent is not set
                         hasAmbiguousParents = true;
@@ -1658,6 +1663,13 @@ private static List<String> getAllParentsName(
                         if (includeAncestors && isComposedSchema(s)) {
                             names.addAll(getAllParentsName(s, allSchemas, true, seenNames));
                         }
+                    } else if (hasOneOf(s)) {
+                        // a $ref to a oneOf schema is treated as a parent even without
+                        // a discriminator
+                        names.add(parentName);
+                        if (includeAncestors && isComposedSchema(s)) {
+                            names.addAll(getAllParentsName(s, allSchemas, true, seenNames));
+                        }
                     } else {
                         // not a parent since discriminator.propertyName is not set
                     }

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

@@ -1171,6 +1171,79 @@ public void testAllOfRequired() {
         assertEquals(getRequiredVars(childModel), Collections.singletonList("name"));
     }
 
+    @Test
+    public void testAllOfWithOneOfRefNoDiscriminator() {
+        final OpenAPI openAPI = TestUtils.parseFlattenSpec("src/test/resources/3_0/allOf_oneOf_noDiscriminator.yaml");
+        DefaultCodegen codegen = new DefaultCodegen();
+        codegen.supportsInheritance = true;
+        codegen.setOpenAPI(openAPI);
+
+        // ParentC uses allOf with a $ref to Child (a oneOf without discriminator).
+        // Child should be recognized as a parent, not flattened.
+        Schema parentCSchema = openAPI.getComponents().getSchemas().get("ParentC");
+        CodegenModel parentCModel = codegen.fromModel("ParentC", parentCSchema);
+        assertEquals("Child", parentCModel.parentSchema);
+        assertEquals("Child", parentCModel.parent);
+
+        // Only the own property "type" should be in vars, not the oneOf variant properties
+        List<String> varNames = parentCModel.vars.stream().map(v -> v.name).collect(Collectors.toList());
+        assertTrue(varNames.contains("type"), "vars should contain 'type'");
+        assertFalse(varNames.contains("xOnlyField"), "vars should not contain variant-specific 'xOnlyField'");
+        assertFalse(varNames.contains("yOnlyField"), "vars should not contain variant-specific 'yOnlyField'");
+        assertFalse(varNames.contains("zOnlyField"), "vars should not contain variant-specific 'zOnlyField'");
+
+        // allVars should also not contain flattened variant properties
+        List<String> allVarNames = parentCModel.allVars.stream().map(v -> v.name).collect(Collectors.toList());
+        assertFalse(allVarNames.contains("xOnlyField"), "allVars should not contain variant-specific 'xOnlyField'");
+        assertFalse(allVarNames.contains("yOnlyField"), "allVars should not contain variant-specific 'yOnlyField'");
+        assertFalse(allVarNames.contains("zOnlyField"), "allVars should not contain variant-specific 'zOnlyField'");
+    }
+
+    @Test
+    public void testAllOfWithOneOfRefNoDiscriminatorNoInheritance() {
+        final OpenAPI openAPI = TestUtils.parseFlattenSpec("src/test/resources/3_0/allOf_oneOf_noDiscriminator.yaml");
+        DefaultCodegen codegen = new DefaultCodegen();
+        codegen.supportsInheritance = false;
+        codegen.setOpenAPI(openAPI);
+
+        // Even without supportsInheritance, variant properties should not be flattened
+        Schema parentCSchema = openAPI.getComponents().getSchemas().get("ParentC");
+        CodegenModel parentCModel = codegen.fromModel("ParentC", parentCSchema);
+
+        List<String> varNames = parentCModel.vars.stream().map(v -> v.name).collect(Collectors.toList());
+        assertFalse(varNames.contains("xOnlyField"), "vars should not contain variant-specific 'xOnlyField'");
+        assertFalse(varNames.contains("yOnlyField"), "vars should not contain variant-specific 'yOnlyField'");
+        assertFalse(varNames.contains("zOnlyField"), "vars should not contain variant-specific 'zOnlyField'");
+    }
+
+    @Test
+    public void testAllOfWithOneOfRefPreservesWrapperProperties() {
+        final OpenAPI openAPI = TestUtils.parseFlattenSpec("src/test/resources/3_0/allOf_oneOf_noDiscriminator.yaml");
+        DefaultCodegen codegen = new DefaultCodegen();
+        codegen.supportsInheritance = true;
+        codegen.setOpenAPI(openAPI);
+
+        // ChildWithSharedFields is a oneOf wrapper that also declares its own
+        // properties (wrapperOptionalField, wrapperRequiredField). When ParentWithSharedFields
+        // inherits from it via allOf, those wrapper-level properties must still flow
+        // through to allProperties/allRequired — only the variant-specific properties
+        // should be suppressed.
+        Schema parentSchema = openAPI.getComponents().getSchemas().get("ParentWithSharedFields");
+        CodegenModel parentModel = codegen.fromModel("ParentWithSharedFields", parentSchema);
+
+        List<String> allVarNames = parentModel.allVars.stream().map(v -> v.name).collect(Collectors.toList());
+        assertTrue(allVarNames.contains("wrapperOptionalField"), "allVars should contain wrapper-level 'wrapperOptionalField'");
+        assertTrue(allVarNames.contains("wrapperRequiredField"), "allVars should contain wrapper-level 'wrapperRequiredField'");
+        assertTrue(allVarNames.contains("extraField"), "allVars should contain inline allOf 'extraField'");
+        assertFalse(allVarNames.contains("xOnlyField"), "allVars should not contain variant-specific 'xOnlyField'");
+        assertFalse(allVarNames.contains("yOnlyField"), "allVars should not contain variant-specific 'yOnlyField'");
+        assertFalse(allVarNames.contains("zOnlyField"), "allVars should not contain variant-specific 'zOnlyField'");
+
+        List<String> requiredVarNames = parentModel.requiredVars.stream().map(v -> v.name).collect(Collectors.toList());
+        assertTrue(requiredVarNames.contains("wrapperRequiredField"), "requiredVars should include wrapper-level required 'wrapperRequiredField'");
+        assertTrue(requiredVarNames.contains("extraField"), "requiredVars should include inline allOf required 'extraField'");
+    }
+
     @Test
     public void testAllOfSingleAndDoubleRefWithOwnPropsNoDiscriminator() {
         final OpenAPI openAPI = TestUtils.parseFlattenSpec("src/test/resources/3_0/allOf_composition.yaml");

modules/openapi-generator/src/test/resources/3_0/allOf_oneOf_noDiscriminator.yaml

@@ -0,0 +1,94 @@
+openapi: 3.0.2
+info:
+  title: allOf with oneOf (no discriminator) test
+  version: 1.0.0
+paths:
+  /parent:
+    get:
+      responses:
+        '200':
+          description: OK
+          content:
+            application/json:
+              schema:
+                $ref: '#/components/schemas/ParentC'
+  /parent-shared:
+    get:
+      responses:
+        '200':
+          description: OK
+          content:
+            application/json:
+              schema:
+                $ref: '#/components/schemas/ParentWithSharedFields'
+components:
+  schemas:
+    ParentC:
+      allOf:
+        - type: object
+          required: [type]
+          properties:
+            type:
+              type: string
+        - $ref: "#/components/schemas/Child"
+
+    Child:
+      oneOf:
+        - $ref: "#/components/schemas/ChildX"
+        - $ref: "#/components/schemas/ChildY"
+        - $ref: "#/components/schemas/ChildZ"
+
+    ParentWithSharedFields:
+      allOf:
+        - $ref: "#/components/schemas/ChildWithSharedFields"
+        - type: object
+          required: [extraField]
+          properties:
+            extraField:
+              type: string
+
+    ChildWithSharedFields:
+      type: object
+      required: [wrapperRequiredField]
+      properties:
+        wrapperOptionalField:
+          type: string
+        wrapperRequiredField:
+          type: string
+      oneOf:
+        - $ref: "#/components/schemas/ChildX"
+        - $ref: "#/components/schemas/ChildY"
+        - $ref: "#/components/schemas/ChildZ"
+
+    ChildX:
+      type: object
+      required: [kind, sharedField, xOnlyField]
+      properties:
+        kind:
+          type: string
+        sharedField:
+          type: string
+        xOnlyField:
+          type: string
+
+    ChildY:
+      type: object
+      required: [kind, sharedField, yOnlyField]
+      properties:
+        kind:
+          type: string
+        sharedField:
+          type: string
+        yOnlyField:
+          type: string
+
+    ChildZ:
+      type: object
+      required: [kind, sharedField, zOnlyField]
+      properties:
+        kind:
+          type: string
+        sharedField:
+          type: string
+        zOnlyField:
+          type: integer

samples/client/petstore/csharp/generichost/latest/InlineEnumAnyOf/src/Org.OpenAPITools/Model/IconsSizeParameter.cs

@@ -35,7 +35,7 @@ public partial class IconsSizeParameter : IValidatableObject
         /// </summary>
         /// <param name="iconsSizeParameterAnyOf"></param>
         /// <param name="int"></param>
-        internal IconsSizeParameter(Option<IconsSizeParameterAnyOf?> iconsSizeParameterAnyOf, Option<int?> @int)
+        public IconsSizeParameter(Option<IconsSizeParameterAnyOf?> iconsSizeParameterAnyOf, Option<int?> @int)
         {
             IconsSizeParameterAnyOfOption = iconsSizeParameterAnyOf;
             IntOption = @int;

samples/client/petstore/csharp/generichost/latest/OneOfList/src/Org.OpenAPITools/Model/OneOfArrayRequest.cs

@@ -34,7 +34,7 @@ public partial class OneOfArrayRequest : IValidatableObject
         /// Initializes a new instance of the <see cref="OneOfArrayRequest" /> class.
         /// </summary>
         /// <param name="list"></param>
-        internal OneOfArrayRequest(List<string> list)
+        public OneOfArrayRequest(List<string> list)
         {
             List = list;
             OnCreated();
@@ -44,7 +44,7 @@ internal OneOfArrayRequest(List<string> list)
         /// Initializes a new instance of the <see cref="OneOfArrayRequest" /> class.
         /// </summary>
         /// <param name="list1"></param>
-        internal OneOfArrayRequest(List<TestObject> list1)
+        public OneOfArrayRequest(List<TestObject> list1)
         {
             List1 = list1;
             OnCreated();

samples/client/petstore/csharp/generichost/latest/UseDateTimeOffset/docs/models/NullableShape.md

@@ -5,7 +5,6 @@ The value may be a shape or the 'null' value. The 'nullable' attribute was intro
 
 Name | Type | Description | Notes
 ------------ | ------------- | ------------- | -------------
-**ShapeType** | **string** |  | 
 
 [[Back to Model list]](../../README.md#documentation-for-models) [[Back to API list]](../../README.md#documentation-for-api-endpoints) [[Back to README]](../../README.md)
 

samples/client/petstore/csharp/generichost/latest/UseDateTimeOffset/docs/models/Shape.md

@@ -4,7 +4,6 @@
 
 Name | Type | Description | Notes
 ------------ | ------------- | ------------- | -------------
-**ShapeType** | **string** |  | 
 
 [[Back to Model list]](../../README.md#documentation-for-models) [[Back to API list]](../../README.md#documentation-for-api-endpoints) [[Back to README]](../../README.md)
 

samples/client/petstore/csharp/generichost/latest/UseDateTimeOffset/docs/models/ShapeOrNull.md

@@ -5,7 +5,6 @@ The value may be a shape or the 'null' value. This is introduced in OAS schema >
 
 Name | Type | Description | Notes
 ------------ | ------------- | ------------- | -------------
-**ShapeType** | **string** |  | 
 
 [[Back to Model list]](../../README.md#documentation-for-models) [[Back to API list]](../../README.md#documentation-for-api-endpoints) [[Back to README]](../../README.md)
 

samples/client/petstore/csharp/generichost/latest/UseDateTimeOffset/src/Org.OpenAPITools/Model/NullableShape.cs

@@ -117,8 +117,6 @@ public override NullableShape Read(ref Utf8JsonReader utf8JsonReader, Type typeT
 
             JsonTokenType startingTokenType = utf8JsonReader.TokenType;
 
-            Option<string?> shapeType = default;
-
             Quadrilateral? quadrilateral = null;
             Triangle? triangle = null;
 
@@ -167,21 +165,12 @@ public override NullableShape Read(ref Utf8JsonReader utf8JsonReader, Type typeT
 
                     switch (localVarJsonPropertyName)
                     {
-                        case "shapeType":
-                            shapeType = new Option<string?>(utf8JsonReader.GetString()!);
-                            break;
                         default:
                             break;
                     }
                 }
             }
 
-            if (!shapeType.IsSet)
-                throw new ArgumentException("Property is required for class NullableShape.", nameof(shapeType));
-
-            if (shapeType.IsSet && shapeType.Value == null)
-                throw new ArgumentNullException(nameof(shapeType), "Property is not nullable for class NullableShape.");
-
             if (quadrilateral != null)
                 return new NullableShape(quadrilateral);
 

samples/client/petstore/csharp/generichost/latest/UseDateTimeOffset/src/Org.OpenAPITools/Model/OneOfString.cs

@@ -34,7 +34,7 @@ public partial class OneOfString : IValidatableObject
         /// Initializes a new instance of the <see cref="OneOfString" /> class.
         /// </summary>
         /// <param name="string"></param>
-        internal OneOfString(string @string)
+        public OneOfString(string @string)
         {
             String = @string;
             OnCreated();

samples/client/petstore/csharp/generichost/latest/UseDateTimeOffset/src/Org.OpenAPITools/Model/PolymorphicProperty.cs

@@ -34,7 +34,7 @@ public partial class PolymorphicProperty : IValidatableObject
         /// Initializes a new instance of the <see cref="PolymorphicProperty" /> class.
         /// </summary>
         /// <param name="bool"></param>
-        internal PolymorphicProperty(bool @bool)
+        public PolymorphicProperty(bool @bool)
         {
             Bool = @bool;
             OnCreated();
@@ -44,7 +44,7 @@ internal PolymorphicProperty(bool @bool)
         /// Initializes a new instance of the <see cref="PolymorphicProperty" /> class.
         /// </summary>
         /// <param name="string"></param>
-        internal PolymorphicProperty(string @string)
+        public PolymorphicProperty(string @string)
         {
             String = @string;
             OnCreated();
@@ -54,7 +54,7 @@ internal PolymorphicProperty(string @string)
         /// Initializes a new instance of the <see cref="PolymorphicProperty" /> class.
         /// </summary>
         /// <param name="object"></param>
-        internal PolymorphicProperty(Object @object)
+        public PolymorphicProperty(Object @object)
         {
             Object = @object;
             OnCreated();
@@ -64,7 +64,7 @@ internal PolymorphicProperty(Object @object)
         /// Initializes a new instance of the <see cref="PolymorphicProperty" /> class.
         /// </summary>
         /// <param name="list"></param>
-        internal PolymorphicProperty(List<string> list)
+        public PolymorphicProperty(List<string> list)
         {
             List = list;
             OnCreated();