[Java] Fix oneOf discriminator type for inline schemas and allOf inheritance

.mvn/wrapper/maven-wrapper.properties

@@ -14,5 +14,5 @@
 # KIND, either express or implied.  See the License for the
 # specific language governing permissions and limitations
 # under the License.
-distributionUrl=https://repo.maven.apache.org/maven2/org/apache/maven/apache-maven/3.8.8/apache-maven-3.8.8-bin.zip
-wrapperUrl=https://repo.maven.apache.org/maven2/org/apache/maven/wrapper/maven-wrapper/3.2.0/maven-wrapper-3.2.0.jar
+distributionUrl=https://repo.maven.apache.org/maven2/org/apache/maven/apache-maven/3.9.16/apache-maven-3.9.16-bin.zip
+wrapperUrl=https://repo.maven.apache.org/maven2/org/apache/maven/wrapper/maven-wrapper/3.3.4/maven-wrapper-3.3.4.jar

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

@@ -3690,8 +3690,18 @@ protected Schema getDiscriminatorSchema(Schema schema, String discriminatorName)
      * @param discriminatorPropertyName The name of the discriminator property.
      */
     protected String getDiscriminatorPropertyType(Schema schema, String discriminatorPropertyName) {
-        return DiscriminatorUtils.getDiscriminatorPropertyType(schema, discriminatorPropertyName)
-                .map(this::toModelName)
+        return DiscriminatorUtils.recursiveGetDiscriminatorPropertySchema(openAPI, getLegacyDiscriminatorBehavior(), schema, discriminatorPropertyName)
+                .map(discSchema -> {
+                    if (discSchema.get$ref() != null) {
+                        // $ref to a named model (e.g. a top-level enum): use the model name.
+                        return toModelName(ModelUtils.getSimpleRef(discSchema.get$ref()));
+                    }
+                    // Inline schema (inline enum, uri, ...): resolve via the same pipeline the
+                    // concrete model classes use so the oneOf interface getter type matches.
+                    // Keep String for typeless const (isAnyType) to avoid resolving to Object.
+                    CodegenProperty cp = fromProperty(discriminatorPropertyName, discSchema);
+                    return (cp.isAnyType || cp.datatypeWithEnum == null) ? typeMapping.get("string") : cp.datatypeWithEnum;
+                })
                 .orElseGet(() -> typeMapping.get("string"));
     }
 

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

@@ -49,6 +49,67 @@ public static Schema getDiscriminatorSchema(Schema schema, String discriminatorN
         return discSchema;
     }
 
+    /**
+     * Recursively resolve the schema of the discriminator property, descending into composed
+     * (allOf/oneOf/anyOf) schemas and following $refs. Mirrors the traversal of
+     * {@link #recursiveGetDiscriminator} but returns the property {@link Schema} rather than the
+     * {@link Discriminator} object, so the two recursive lookups share a single pass through the
+     * schema hierarchy.
+     *
+     * @param openAPI                     The OpenAPI specification (used to dereference $refs).
+     * @param legacyDiscriminatorBehavior Whether legacy discriminator behaviour is enabled.
+     * @param schema                      The schema that may (transitively) declare the discriminator property.
+     * @param discPropName                The name of the discriminator property.
+     * @param visitedSchemas              Schemas already visited, to guard against cycles.
+     * @return the discriminator property schema, or {@code null} if it cannot be resolved.
+     */
+    public static Optional<Schema> recursiveGetDiscriminatorPropertySchema(OpenAPI openAPI, boolean legacyDiscriminatorBehavior, Schema schema, String discPropName) {
+        return Optional.ofNullable(recursiveGetDiscriminatorPropertySchema(openAPI, legacyDiscriminatorBehavior, schema, discPropName, new ArrayList<>()));
+    }
+
+    private static Schema recursiveGetDiscriminatorPropertySchema(
+            OpenAPI openAPI,
+            boolean legacyDiscriminatorBehavior,
+            Schema schema,
+            String discPropName,
+            ArrayList<Schema> visitedSchemas) {
+        Schema refSchema = ModelUtils.getReferencedSchema(openAPI, schema);
+        Schema propSchema = getDiscriminatorSchema(refSchema, discPropName);
+        if (propSchema != null) {
+            return propSchema;
+        }
+        if (legacyDiscriminatorBehavior) {
+            return null;
+        }
+        for (Schema s : visitedSchemas) {
+            if (s == refSchema) {
+                return null;
+            }
+        }
+        visitedSchemas.add(refSchema);
+        if (ModelUtils.isComposedSchema(refSchema)) {
+            if (refSchema.getAllOf() != null) {
+                for (Object allOf : refSchema.getAllOf()) {
+                    Schema found = recursiveGetDiscriminatorPropertySchema(openAPI, legacyDiscriminatorBehavior, (Schema) allOf, discPropName, visitedSchemas);
+                    if (found != null) return found;
+                }
+            }
+            if (ModelUtils.hasOneOf(refSchema)) {
+                for (Object oneOf : refSchema.getOneOf()) {
+                    Schema found = recursiveGetDiscriminatorPropertySchema(openAPI, legacyDiscriminatorBehavior, (Schema) oneOf, discPropName, visitedSchemas);
+                    if (found != null) return found;
+                }
+            }
+            if (ModelUtils.hasAnyOf(refSchema)) {
+                for (Object anyOf : refSchema.getAnyOf()) {
+                    Schema found = recursiveGetDiscriminatorPropertySchema(openAPI, legacyDiscriminatorBehavior, (Schema) anyOf, discPropName, visitedSchemas);
+                    if (found != null) return found;
+                }
+            }
+        }
+        return null;
+    }
+
     /**
      * Recursively look in Schema sc for the discriminator and return it
      *

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

@@ -2000,6 +2000,37 @@ public void testDiscriminatorWithMappingIssue14731() {
                 .content().doesNotContain("@JsonTypeName");
     }
 
+    @Test
+    public void testOneOfInterfaceInheritedEnumDiscriminator() {
+        final Path output = newTempFolder();
+        final OpenAPI openAPI = new OpenAPIParser()
+                .readLocation("src/test/resources/3_0/oneOfDiscriminator.yaml", null, new ParseOptions())
+                .getOpenAPI();
+
+        // resttemplate (unlike the default okhttp-gson) renders oneOf as interfaces, so it uses the
+        // base Java/oneof_interface template that emits the discriminator getter type.
+        final JavaClientCodegen codegen = new JavaClientCodegen();
+        codegen.setLibrary("resttemplate");
+        codegen.setOutputDir(output.toString());
+        codegen.setUseOneOfInterfaces(true);
+        codegen.setLegacyDiscriminatorBehavior(false);
+
+        final ClientOptInput input = new ClientOptInput().openAPI(openAPI).config(codegen);
+
+        DefaultGenerator generator = new DefaultGenerator();
+        generator.setGeneratorPropertyDefault(CodegenConstants.MODELS, "true");
+        generator.setGeneratorPropertyDefault(CodegenConstants.APIS, "false");
+        generator.setGeneratorPropertyDefault(CodegenConstants.MODEL_TESTS, "false");
+        generator.setGeneratorPropertyDefault(CodegenConstants.MODEL_DOCS, "false");
+        generator.setGeneratorPropertyDefault(CodegenConstants.SUPPORTING_FILES, "false");
+        generator.opts(input).generate();
+
+        // Issue #22541: the inline-enum discriminator inherited from a base schema via allOf must
+        // resolve to the enum type in the oneOf interface getter, not String.
+        assertThat(output.resolve("src/main/java/org/openapitools/client/model/PetResponseEnumDisc.java"))
+                .content().contains("public PetTypeEnum getPetType();");
+    }
+
     @Test
     public void testDiscriminatorWithoutMappingIssue14731() {
         final Path output = newTempFolder();

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

@@ -21,6 +21,7 @@
 import org.openapitools.codegen.DefaultGenerator;
 import org.openapitools.codegen.TestUtils;
 import org.openapitools.codegen.config.CodegenConfigurator;
+import org.openapitools.codegen.languages.AbstractJavaCodegen;
 import org.openapitools.codegen.languages.JavaHelidonCommonCodegen;
 import org.testng.Assert;
 import org.testng.annotations.BeforeMethod;
@@ -70,6 +71,35 @@ public void setup() throws IOException {
         mpClientGenerator = new DefaultGenerator();
     }
 
+    @Test
+    public void testOneOfInterfaceInheritedEnumDiscriminator() throws IOException {
+        File output = Files.createTempDirectory("testHelidonEnumDisc").toFile();
+        output.deleteOnExit();
+        String outputDir = output.getAbsolutePath().replace('\\', '/');
+
+        CodegenConfigurator configurator = new CodegenConfigurator()
+                .setGeneratorName("java-helidon-client")
+                .setLibrary("mp")
+                .setInputSpec("src/test/resources/3_0/oneOfDiscriminator.yaml")
+                .addAdditionalProperty(AbstractJavaCodegen.USE_ONE_OF_INTERFACES, true)
+                .addAdditionalProperty(CodegenConstants.LEGACY_DISCRIMINATOR_BEHAVIOR, false)
+                .setOutputDir(outputDir);
+
+        DefaultGenerator generator = new DefaultGenerator();
+        generator.setGeneratorPropertyDefault(CodegenConstants.MODELS, "true");
+        generator.setGeneratorPropertyDefault(CodegenConstants.APIS, "false");
+        generator.setGeneratorPropertyDefault(CodegenConstants.SUPPORTING_FILES, "false");
+        generator.setGeneratorPropertyDefault(CodegenConstants.MODEL_TESTS, "false");
+        generator.setGeneratorPropertyDefault(CodegenConstants.MODEL_DOCS, "false");
+        generator.opts(configurator.toClientOptInput()).generate();
+
+        // Issue #22541: the inline-enum discriminator inherited from a base schema via allOf must
+        // resolve to the enum type in the oneOf interface getter, not String.
+        TestUtils.assertFileContains(
+                Paths.get(outputDir + "/src/main/java/org/openapitools/client/model/PetResponseEnumDisc.java"),
+                "PetTypeEnum getPetType()");
+    }
+
     @Test
     public void defaultVersionTest() {
         runServerVersionTest(null, null);

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

@@ -47,6 +47,21 @@ public void testInitialConfigValues() throws Exception {
         configAssert.assertValue(CodegenConstants.INVOKER_PACKAGE, codegen::getInvokerPackage, "org.openapitools");
     }
 
+    @Test
+    public void testOneOfInterfaceInheritedEnumDiscriminator() {
+        JavaMicronautClientCodegen codegen = new JavaMicronautClientCodegen();
+        codegen.setUseOneOfInterfaces(true);
+        codegen.setLegacyDiscriminatorBehavior(false);
+        String outputPath = generateFiles(codegen, "src/test/resources/3_0/oneOfDiscriminator.yaml",
+                CodegenConstants.MODELS);
+
+        // Issue #22541: the inline-enum discriminator is inherited from a base schema via allOf, so
+        // the oneOf interface getter must resolve to the enum type, not String
+        // (DefaultCodegen.getDiscriminatorPropertyType).
+        assertFileContains(outputPath + "src/main/java/org/openapitools/model/PetResponseEnumDisc.java",
+                "public PetTypeEnum getPetType();");
+    }
+
     @Test
     public void testApiAndModelFilesPresent() {
         JavaMicronautClientCodegen codegen = new JavaMicronautClientCodegen();

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

@@ -2139,6 +2139,92 @@ public void testDiscriminatorWithoutMappingIssue14731() throws IOException {
         assertFileContains(Paths.get(outputPath + "/src/main/java/org/openapitools/model/ChildWithoutMappingBDTO.java"), "@JsonTypeName");
     }
 
+    @Test
+    void testOneOfWithInheritedEnumDiscriminator() throws IOException {
+        File output = Files.createTempDirectory("test").toFile().getCanonicalFile();
+        output.deleteOnExit();
+        String outputPath = output.getAbsolutePath().replace('\\', '/');
+        OpenAPI openAPI = new OpenAPIParser()
+                .readLocation("src/test/resources/3_0/oneOfDiscriminator.yaml", null, new ParseOptions()).getOpenAPI();
+
+        SpringCodegen codegen = new SpringCodegen();
+        codegen.setOutputDir(output.getAbsolutePath());
+        codegen.additionalProperties().put(CXFServerFeatures.LOAD_TEST_DATA_FROM_FILE, "true");
+        codegen.setUseOneOfInterfaces(true);
+
+        ClientOptInput input = new ClientOptInput();
+        input.openAPI(openAPI);
+        input.config(codegen);
+
+        DefaultGenerator generator = new DefaultGenerator();
+        codegen.setHateoas(true);
+        generator.setGenerateMetadata(false);
+        generator.setGeneratorPropertyDefault(CodegenConstants.MODEL_TESTS, "false");
+        generator.setGeneratorPropertyDefault(CodegenConstants.MODEL_DOCS, "false");
+        generator.setGeneratorPropertyDefault(CodegenConstants.MODELS, "true");
+        generator.setGeneratorPropertyDefault(CodegenConstants.LEGACY_DISCRIMINATOR_BEHAVIOR, "false");
+
+        codegen.setUseOneOfInterfaces(true);
+        codegen.setLegacyDiscriminatorBehavior(false);
+
+        generator.opts(input).generate();
+
+        // The discriminator (inline enum) is inherited from the base PetEnumDisc via allOf. The
+        // oneOf interface getter must use the same enum type as the concrete base class, not
+        // String, otherwise the generated code does not compile (issue #22541).
+        assertFileContains(
+                Paths.get(outputPath + "/src/main/java/org/openapitools/model/PetResponseEnumDisc.java"),
+                "public PetTypeEnum getPetType();"
+        );
+        assertFileContains(
+                Paths.get(outputPath + "/src/main/java/org/openapitools/model/PetEnumDisc.java"),
+                "public PetTypeEnum getPetType()"
+        );
+    }
+
+    @Test
+    void testOneOfWithInheritedUriDiscriminator() throws IOException {
+        File output = Files.createTempDirectory("test").toFile().getCanonicalFile();
+        output.deleteOnExit();
+        String outputPath = output.getAbsolutePath().replace('\\', '/');
+        OpenAPI openAPI = new OpenAPIParser()
+                .readLocation("src/test/resources/3_0/oneOfDiscriminator.yaml", null, new ParseOptions()).getOpenAPI();
+
+        SpringCodegen codegen = new SpringCodegen();
+        codegen.setOutputDir(output.getAbsolutePath());
+        codegen.additionalProperties().put(CXFServerFeatures.LOAD_TEST_DATA_FROM_FILE, "true");
+        codegen.setUseOneOfInterfaces(true);
+
+        ClientOptInput input = new ClientOptInput();
+        input.openAPI(openAPI);
+        input.config(codegen);
+
+        DefaultGenerator generator = new DefaultGenerator();
+        codegen.setHateoas(true);
+        generator.setGenerateMetadata(false);
+        generator.setGeneratorPropertyDefault(CodegenConstants.MODEL_TESTS, "false");
+        generator.setGeneratorPropertyDefault(CodegenConstants.MODEL_DOCS, "false");
+        generator.setGeneratorPropertyDefault(CodegenConstants.MODELS, "true");
+        generator.setGeneratorPropertyDefault(CodegenConstants.LEGACY_DISCRIMINATOR_BEHAVIOR, "false");
+
+        codegen.setUseOneOfInterfaces(true);
+        codegen.setLegacyDiscriminatorBehavior(false);
+
+        generator.opts(input).generate();
+
+        // The discriminator (string, format: uri) is inherited from the base PetUriDisc via allOf.
+        // The oneOf interface getter must use URI, matching the concrete base class, not String,
+        // otherwise the generated code does not compile (issue #18693).
+        assertFileContains(
+                Paths.get(outputPath + "/src/main/java/org/openapitools/model/PetResponseUriDisc.java"),
+                "public URI getPetType();"
+        );
+        assertFileContains(
+                Paths.get(outputPath + "/src/main/java/org/openapitools/model/PetUriDisc.java"),
+                "public URI getPetType()"
+        );
+    }
+
     @Test
     void testOneOfWithEnumDiscriminator() throws IOException {
         File output = Files.createTempDirectory("test").toFile().getCanonicalFile();

modules/openapi-generator/src/test/java/org/openapitools/codegen/kotlin/spring/KotlinSpringServerCodegenTest.java

@@ -121,6 +121,39 @@ public void testNoRequestMappingAnnotation_spring_cloud_default() throws IOExcep
         );
     }
 
+    @Test
+    public void testOneOfInterfaceInheritedEnumDiscriminator() throws IOException {
+        // Cross-generator check for the DefaultCodegen discriminator-type fix: the kotlin-spring
+        // oneof_interface template emits the discriminator getter type too. Issue #22541: the
+        // inline-enum discriminator is inherited from a base schema via allOf, so the sealed
+        // interface must use the enum type rather than String.
+        File output = Files.createTempDirectory("test").toFile().getCanonicalFile();
+        output.deleteOnExit();
+
+        final KotlinSpringServerCodegen codegen = new KotlinSpringServerCodegen();
+        codegen.setOutputDir(output.getAbsolutePath());
+        codegen.setUseOneOfInterfaces(true);
+        codegen.setLegacyDiscriminatorBehavior(false);
+
+        DefaultGenerator generator = new DefaultGenerator();
+        generator.setGenerateMetadata(false);
+        generator.setGeneratorPropertyDefault(CodegenConstants.MODELS, "true");
+        generator.setGeneratorPropertyDefault(CodegenConstants.APIS, "false");
+        generator.setGeneratorPropertyDefault(CodegenConstants.MODEL_TESTS, "false");
+        generator.setGeneratorPropertyDefault(CodegenConstants.MODEL_DOCS, "false");
+        generator.setGeneratorPropertyDefault(CodegenConstants.LEGACY_DISCRIMINATOR_BEHAVIOR, "false");
+
+        generator.opts(new ClientOptInput()
+                        .openAPI(TestUtils.parseSpec("src/test/resources/3_0/oneOfDiscriminator.yaml"))
+                        .config(codegen))
+                .generate();
+
+        assertFileContains(
+                Paths.get(output + "/src/main/kotlin/org/openapitools/model/PetResponseEnumDisc.kt"),
+                "val petType: PetType"
+        );
+    }
+
     @Test
     public void testNoRequestMappingAnnotationNone() throws IOException {
         File output = generatePetstoreWithRequestMappingMode(KotlinSpringServerCodegen.RequestMappingMode.none);

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

@@ -298,3 +298,61 @@ components:
         - $ref: '#/components/schemas/FruitType'
       discriminator:
         propertyName: fruitType
+    # oneOf interface whose discriminator property is an inline enum inherited from a shared base
+    # schema (PetEnumDisc) via allOf. The interface getter must use the same enum type the
+    # concrete classes generate, not String. Ref: issue #22541.
+    PetResponseEnumDisc:
+      oneOf:
+        - $ref: '#/components/schemas/DogEnumDisc'
+        - $ref: '#/components/schemas/CatEnumDisc'
+    PetEnumDisc:
+      type: object
+      required:
+        - petType
+      properties:
+        petType:
+          type: string
+          enum:
+            - dog
+            - cat
+      discriminator:
+        propertyName: petType
+        mapping:
+          dog: DogEnumDisc
+          cat: CatEnumDisc
+    DogEnumDisc:
+      type: object
+      allOf:
+        - $ref: '#/components/schemas/PetEnumDisc'
+    CatEnumDisc:
+      type: object
+      allOf:
+        - $ref: '#/components/schemas/PetEnumDisc'
+    # oneOf interface whose discriminator property is an inline string with a non-string format
+    # (uri) inherited from a shared base schema (PetUriDisc) via allOf. The interface getter must
+    # use URI, matching the concrete classes, not String. Ref: issue #18693.
+    PetResponseUriDisc:
+      oneOf:
+        - $ref: '#/components/schemas/DogUriDisc'
+        - $ref: '#/components/schemas/CatUriDisc'
+    PetUriDisc:
+      type: object
+      required:
+        - petType
+      properties:
+        petType:
+          type: string
+          format: uri
+      discriminator:
+        propertyName: petType
+        mapping:
+          dog: DogUriDisc
+          cat: CatUriDisc
+    DogUriDisc:
+      type: object
+      allOf:
+        - $ref: '#/components/schemas/PetUriDisc'
+    CatUriDisc:
+      type: object
+      allOf:
+        - $ref: '#/components/schemas/PetUriDisc'