[#4650] Fix StackOverflowError for recursive composite schemas (#11620)

The generator ran into a loop when a composite schema recursively added itself. This change provides a reproducing example and fixes the issue by extending DefaultCodegen#addProperties() by an additional circuit breaker parameter.

When additionalProperties() is called with a schema instance for which the properties have already been added, the method directly returns and does not run into the loop.

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

@@ -2535,14 +2535,14 @@ public class DefaultCodegen implements CodegenConfig {
                 if (allDefinitions != null && refSchema != null) {
                     if (allParents.contains(ref) && supportsMultipleInheritance) {
                         // multiple inheritance
-                        addProperties(allProperties, allRequired, refSchema);
+                        addProperties(allProperties, allRequired, refSchema, new HashSet<>());
                     } else if (parentName != null && parentName.equals(ref) && supportsInheritance) {
                         // single inheritance
-                        addProperties(allProperties, allRequired, refSchema);
+                        addProperties(allProperties, allRequired, refSchema, new HashSet<>());
                     } else {
                         // composition
-                        addProperties(properties, required, refSchema);
+                        addProperties(properties, required, refSchema, new HashSet<>());
-                        addProperties(allProperties, allRequired, refSchema);
+                        addProperties(allProperties, allRequired, refSchema, new HashSet<>());
                     }
                 }
 
@@ -2579,10 +2579,10 @@ public class DefaultCodegen implements CodegenConfig {
             if (component.get$ref() == null) {
                 if (component != null) {
                     // component is the child schema
-                    addProperties(properties, required, component);
+                    addProperties(properties, required, component, new HashSet<>());
 
                     // includes child's properties (all, required) in allProperties, allRequired
-                    addProperties(allProperties, allRequired, component);
+                    addProperties(allProperties, allRequired, component, new HashSet<>());
                 }
                 break; // at most one child only
             }
@@ -3266,14 +3266,18 @@ public class DefaultCodegen implements CodegenConfig {
      * @param properties     all properties
      * @param required       required property only
      * @param schema         schema in which the properties will be added to the lists
+     * @param visitedSchemas circuit-breaker - the schemas with which the method was called before for recursive structures
      */
-    protected void addProperties(Map<String, Schema> properties, List<String> required, Schema schema) {
+    protected void addProperties(Map<String, Schema> properties, List<String> required, Schema schema, Set<Schema> visitedSchemas) {
+        if (!visitedSchemas.add(schema)) {
+            return;
+        }
         if (schema instanceof ComposedSchema) {
             ComposedSchema composedSchema = (ComposedSchema) schema;
 
             if (composedSchema.getAllOf() != null) {
                 for (Schema component : composedSchema.getAllOf()) {
-                    addProperties(properties, required, component);
+                    addProperties(properties, required, component, visitedSchemas);
                 }
             }
 
@@ -3283,13 +3287,13 @@ public class DefaultCodegen implements CodegenConfig {
 
             if (composedSchema.getOneOf() != null) {
                 for (Schema component : composedSchema.getOneOf()) {
-                    addProperties(properties, required, component);
+                    addProperties(properties, required, component, visitedSchemas);
                 }
             }
 
             if (composedSchema.getAnyOf() != null) {
                 for (Schema component : composedSchema.getAnyOf()) {
-                    addProperties(properties, required, component);
+                    addProperties(properties, required, component, visitedSchemas);
                 }
             }
 
@@ -3298,7 +3302,7 @@ public class DefaultCodegen implements CodegenConfig {
 
         if (StringUtils.isNotBlank(schema.get$ref())) {
             Schema interfaceSchema = ModelUtils.getReferencedSchema(this.openAPI, schema);
-            addProperties(properties, required, interfaceSchema);
+            addProperties(properties, required, interfaceSchema, visitedSchemas);
             return;
         }
         if (schema.getProperties() != null) {
@@ -6247,7 +6251,7 @@ public class DefaultCodegen implements CodegenConfig {
         // TODO in the future have this return one codegenParameter of type object or composed which includes all definition
         // that will be needed for complex composition use cases
         // https://github.com/OpenAPITools/openapi-generator/issues/10415
-        addProperties(properties, allRequired, schema);
+        addProperties(properties, allRequired, schema, new HashSet<>());
 
         if (!properties.isEmpty()) {
             for (Map.Entry<String, Schema> entry : properties.entrySet()) {

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

@@ -629,14 +629,14 @@ public class PythonClientCodegen extends PythonLegacyClientCodegen {
         }
         for (Schema sc : oneOfanyOfSchemas) {
             Schema refSchema = ModelUtils.getReferencedSchema(this.openAPI, sc);
-            addProperties(otherProperties, otherRequired, refSchema);
+            addProperties(otherProperties, otherRequired, refSchema, new HashSet<>());
         }
         Set<String> otherRequiredSet = new HashSet<>(otherRequired);
 
         List<Schema> allOf = cs.getAllOf();
         if ((schema.getProperties() != null && !schema.getProperties().isEmpty()) || allOf != null) {
             // NOTE: this function also adds the allOf properties inside schema
-            addProperties(selfProperties, selfRequired, schema);
+            addProperties(selfProperties, selfRequired, schema, new HashSet<>());
         }
         if (result.discriminator != null) {
             selfRequired.add(result.discriminator.getPropertyBaseName());

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

@@ -744,4 +744,24 @@ public class DefaultGeneratorTest {
             templates.toFile().delete();
         }
     }
+
+    @Test
+    public void testRecursionBug4650() {
+        OpenAPI openAPI = TestUtils.parseFlattenSpec("src/test/resources/bugs/recursion-bug-4650.yaml");
+        ClientOptInput opts = new ClientOptInput();
+        opts.openAPI(openAPI);
+        DefaultCodegen config = new DefaultCodegen();
+        config.setStrictSpecBehavior(false);
+        opts.config(config);
+        final DefaultGenerator generator = new DefaultGenerator();
+        generator.opts(opts);
+        generator.configureGeneratorProperties();
+
+        List<File> files = new ArrayList<>();
+        List<String> filteredSchemas = ModelUtils.getSchemasUsedOnlyInFormParam(openAPI);
+        List<Object> allModels = new ArrayList<>();
+        // The bug causes a StackOverflowError when calling generateModels
+        generator.generateModels(files, allModels, filteredSchemas);
+        // all fine, we have passed
+    }
 }

modules/openapi-generator/src/test/resources/bugs/recursion-bug-4650.yaml

@@ -0,0 +1,64 @@
+openapi: 3.0.1
+info:
+  title: Test
+  version: v1
+paths:
+  /api/v1/filters:
+    get:
+      responses:
+        '200':
+          description: default response
+          content:
+            '*/*':
+              schema:
+                $ref: '#/components/schemas/Filter'
+components:
+  schemas:
+    AndFilter:
+      type: object
+      allOf:
+        - $ref: '#/components/schemas/Filter'
+        - type: object
+          properties:
+            operator:
+              type: string
+              default: and
+              enum:
+                - and
+                - or
+            filters:
+              type: array
+              items:
+                $ref: '#/components/schemas/Filter'
+    Filter:
+      type: object
+      properties:
+        operator:
+          type: string
+          enum:
+            - and
+            - or
+      example:
+        operator: eq
+        field: name
+        value: john
+      discriminator:
+        propertyName: operator
+        mapping:
+          and: '#/components/schemas/AndFilter'
+          or: '#/components/schemas/OrFilter'
+      oneOf:
+        - $ref: '#/components/schemas/AndFilter'
+        - $ref: '#/components/schemas/OrFilter'
+    OrFilter:
+      type: object
+      allOf:
+        - $ref: '#/components/schemas/Filter'
+        - type: object
+          properties:
+            operator:
+              type: string
+              default: or
+              enum:
+                - and
+                - or