Fix issue #15298

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

@@ -3147,8 +3147,12 @@ protected void setAddProps(Schema schema, IJsonSchemaValidationProperties proper
      * @param sc                 The Schema that may contain the discriminator
      * @param discPropName       The String that is the discriminator propertyName in the schema
      */
-    private CodegenProperty discriminatorFound(String composedSchemaName, Schema sc, String discPropName, OpenAPI openAPI) {
+    private CodegenProperty discriminatorFound(String composedSchemaName, Schema sc, String discPropName, OpenAPI openAPI, Set<Schema> visitedSchemas) {
         Schema refSchema = ModelUtils.getReferencedSchema(openAPI, sc);
+        if (visitedSchemas.contains(refSchema)) {
+            return null;
+        }
+        visitedSchemas.add(refSchema);
         if (refSchema.getProperties() != null && refSchema.getProperties().get(discPropName) != null) {
             Schema discSchema = (Schema) refSchema.getProperties().get(discPropName);
             CodegenProperty cp = new CodegenProperty();
@@ -3166,7 +3170,7 @@ private CodegenProperty discriminatorFound(String composedSchemaName, Schema sc,
             if (composedSchema.getAllOf() != null) {
                 // If our discriminator is in one of the allOf schemas break when we find it
                 for (Schema allOf : composedSchema.getAllOf()) {
-                    CodegenProperty cp = discriminatorFound(composedSchemaName, allOf, discPropName, openAPI);
+                    CodegenProperty cp = discriminatorFound(composedSchemaName, allOf, discPropName, openAPI, visitedSchemas);
                     if (cp != null) {
                         return cp;
                     }
@@ -3177,7 +3181,7 @@ private CodegenProperty discriminatorFound(String composedSchemaName, Schema sc,
                 CodegenProperty cp = new CodegenProperty();
                 for (Schema oneOf : composedSchema.getOneOf()) {
                     String modelName = ModelUtils.getSimpleRef(oneOf.get$ref());
-                    CodegenProperty thisCp = discriminatorFound(composedSchemaName, oneOf, discPropName, openAPI);
+                    CodegenProperty thisCp = discriminatorFound(composedSchemaName, oneOf, discPropName, openAPI, visitedSchemas);
                     if (thisCp == null) {
                         LOGGER.warn(
                                 "'{}' defines discriminator '{}', but the referenced OneOf schema '{}' is missing {}",
@@ -3200,7 +3204,7 @@ private CodegenProperty discriminatorFound(String composedSchemaName, Schema sc,
                 CodegenProperty cp = new CodegenProperty();
                 for (Schema anyOf : composedSchema.getAnyOf()) {
                     String modelName = ModelUtils.getSimpleRef(anyOf.get$ref());
-                    CodegenProperty thisCp = discriminatorFound(composedSchemaName, anyOf, discPropName, openAPI);
+                    CodegenProperty thisCp = discriminatorFound(composedSchemaName, anyOf, discPropName, openAPI, visitedSchemas);
                     if (thisCp == null) {
                         LOGGER.warn(
                                 "'{}' defines discriminator '{}', but the referenced AnyOf schema '{}' is missing {}",
@@ -3355,7 +3359,8 @@ protected List<MappedModel> getOneOfAnyOfDescendants(String composedSchemaName,
                             "Invalid inline schema defined in oneOf/anyOf in '{}'. Per the OpenApi spec, for this case when a composed schema defines a discriminator, the oneOf/anyOf schemas must use $ref. Change this inline definition to a $ref definition",
                             composedSchemaName);
                 }
-                CodegenProperty df = discriminatorFound(composedSchemaName, sc, discPropName, openAPI);
+                HashSet<Schema> visitedSchemas = new HashSet<>();
+                CodegenProperty df = discriminatorFound(composedSchemaName, sc, discPropName, openAPI, visitedSchemas);
                 String modelName = ModelUtils.getSimpleRef(ref);
                 if (df == null || !df.isString || df.required != true) {
                     String msgSuffix = "";

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

@@ -2666,7 +2666,37 @@ public void testEnumCaseSensitive_issue8084() throws IOException {
                 .bodyContainsLines("if (b.value.equals(value)) {");
     }
 
+    @Test
+    public void shouldNotFallWithNPEOrStackOverflow() throws IOException {
+        File output = Files.createTempDirectory("test").toFile().getCanonicalFile();
+        output.deleteOnExit();
 
+        OpenAPI openAPI = new OpenAPIParser()
+                .readLocation("src/test/resources/3_0/issue_spring_codegen_polymorphism.yaml", null, new ParseOptions()).getOpenAPI();
+
+        SpringCodegen codegen = new SpringCodegen();
+        codegen.setOutputDir(output.getAbsolutePath());
+        codegen.additionalProperties().put(SpringCodegen.DATE_LIBRARY, "java8-localdatetime");
+        codegen.additionalProperties().put(INTERFACE_ONLY, "true");
+        codegen.additionalProperties().put(USE_ONE_OF_INTERFACES, "false");
+        codegen.additionalProperties().put(CodegenConstants.SERIALIZABLE_MODEL, "true");
+        codegen.additionalProperties().put(CodegenConstants.HIDE_GENERATION_TIMESTAMP, "true");
+        codegen.additionalProperties().put(USE_TAGS, "true");
+
+        ClientOptInput input = new ClientOptInput();
+        input.openAPI(openAPI);
+        input.config(codegen);
+
+        DefaultGenerator generator = new DefaultGenerator();
+        generator.setGeneratorPropertyDefault(CodegenConstants.LIBRARY, "spring-cloud");
+        generator.setGeneratorPropertyDefault(CodegenConstants.MODEL_TESTS, "false");
+        generator.setGeneratorPropertyDefault(CodegenConstants.MODEL_DOCS, "false");
+        generator.setGeneratorPropertyDefault(CodegenConstants.APIS, "true");
+        generator.setGeneratorPropertyDefault(CodegenConstants.MODELS, "true");
+        generator.setGeneratorPropertyDefault(CodegenConstants.SUPPORTING_FILES, "false");
+
+        generator.opts(input).generate();
+    }
 
     @Test
     public void multiLineOperationDescription() throws IOException {
@@ -2692,4 +2722,5 @@ public void multiLineTagDescription() throws IOException {
         JavaFileAssert.assertThat(files.get("PingTagApi.java"))
                 .fileContains("This is a multine tag : * tag item 1 * tag item 2 ");
     }
+
 }

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

@@ -0,0 +1,74 @@
+openapi: 3.0.2
+info:
+  title: Polymorphism Java Example
+  version: 1.0.0
+  contact:
+    name: polydectes
+    email: 12345@sharklasers.com
+servers:
+  - url: 'https://localhost'
+tags:
+  - name: Example
+paths:
+  '/animal':
+    post:
+      tags:
+        - Example
+      operationId: createAnAnimal
+      requestBody:
+        required: true
+        content:
+          application/json:
+            schema:
+              $ref: '#/components/schemas/Animal'
+      responses:
+        '200':
+          $ref: '#/components/responses/200-OK'
+        '400':
+          $ref: '#/components/responses/400-BadRequest'
+components:
+  responses:
+    200-OK:
+      description: OK
+      content:
+        application/json:
+          schema:
+            $ref: '#/components/schemas/Animal'
+    400-BadRequest:
+      description: Error
+      content:
+        application/json:
+          schema:
+            $ref: '#/components/schemas/ErrorResponse'
+  schemas:
+    Animal:
+      type: object
+      oneOf:
+        - $ref: '#/components/schemas/Cat'
+        - $ref: '#/components/schemas/Dog'
+      discriminator:
+        propertyName: animalType
+    Cat:
+      type: object
+      allOf:
+        - $ref: '#/components/schemas/Animal'
+      properties:
+        acceptableAsHousepet:
+          type: boolean
+    Dog:
+      type: object
+      allOf:
+        - $ref: '#/components/schemas/Animal'
+      properties:
+        canBeTrained:
+          type: string
+    OkResponse:
+      type: object
+      properties:
+        id:
+          type: string
+    ErrorResponse:
+      type: object
+      properties:
+        message:
+          type: string