[kotlin-server] Add configurable inheritance modes

docs/generators/kotlin-server.md

@@ -34,6 +34,7 @@ These options may be applied as additional-properties (cli) or configOptions (pl
 |groupId|Generated artifact package's organization (i.e. maven groupId).| |org.openapitools|
 |implicitHeaders|Skip header parameters in the generated API methods.| |false|
 |interfaceOnly|Whether to generate only API interface stubs without the server files. This option is currently supported only when using jaxrs-spec library.| |false|
+|inheritanceMode|Strategy for model inheritance generation. Values: `none`, `sealed`, `abstract`, `composition`.|<dl><dt>**none**</dt><dd>Flatten inheritance metadata (no discriminator/parent shaping).</dd><dt>**sealed**</dt><dd>Use sealed/interface-oriented shaping.</dd><dt>**abstract**</dt><dd>Use abstract base class shaping.</dd><dt>**composition**</dt><dd>Flatten inheritance and generate discriminator owners as composition wrappers (`value: Any`).</dd></dl>|sealed (ktor/javalin), abstract (jaxrs-spec)|
 |library|library template (sub-template)|<dl><dt>**ktor**</dt><dd>ktor framework</dd><dt>**ktor2**</dt><dd>ktor (2.x) framework</dd><dt>**jaxrs-spec**</dt><dd>JAX-RS spec only</dd><dt>**javalin5**</dt><dd>Javalin 5</dd><dt>**javalin6**</dt><dd>Javalin 6</dd></dl>|ktor|
 |modelMutable|Create mutable models| |false|
 |omitGradleWrapper|Whether to omit Gradle wrapper for creating a sub project.| |false|

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

@@ -109,6 +109,7 @@ public class KotlinServerCodegen extends AbstractKotlinCodegen implements BeanVa
     @Getter
     @Setter
     private Boolean delegatePatternEnabled = false;
+    private String inheritanceMode;
 
     /**
      * Constructs an instance of `KotlinServerCodegen`.
@@ -184,6 +185,17 @@ public KotlinServerCodegen() {
         addSwitch(USE_JAKARTA_EE, Constants.USE_JAKARTA_EE_DESC, useJakartaEe);
         addSwitch(Constants.FIX_JACKSON_JSON_TYPE_INFO_INHERITANCE, Constants.FIX_JACKSON_JSON_TYPE_INFO_INHERITANCE_DESC, fixJacksonJsonTypeInfoInheritance);
         addSwitch(Constants.DELEGATE_PATTERN, Constants.DELEGATE_PATTERN_DESC, getDelegatePatternEnabled());
+        addOption(Constants.INHERITANCE_MODE, Constants.INHERITANCE_MODE_DESC,
+                defaultInheritanceModeForLibrary(DEFAULT_LIBRARY), buildInheritanceModeOptions());
+    }
+
+    private Map<String, String> buildInheritanceModeOptions() {
+        Map<String, String> options = new HashMap<>();
+        options.put(Constants.INHERITANCE_MODE_NONE, "Flat models (no inheritance-aware shaping)");
+        options.put(Constants.INHERITANCE_MODE_SEALED, "Sealed/interface oriented inheritance");
+        options.put(Constants.INHERITANCE_MODE_ABSTRACT, "Abstract base classes and concrete children");
+        options.put(Constants.INHERITANCE_MODE_COMPOSITION, "Composition wrappers for polymorphism");
+        return options;
     }
 
     @Override
@@ -271,6 +283,37 @@ public void processOpts() {
             LOGGER.info("`library` option is empty. Default to {}", DEFAULT_LIBRARY);
         }
 
+        inheritanceMode = defaultInheritanceModeForLibrary(library);
+        if (additionalProperties.containsKey(Constants.INHERITANCE_MODE)) {
+            String configuredInheritanceMode = String.valueOf(additionalProperties.get(Constants.INHERITANCE_MODE));
+            if (!isValidInheritanceMode(configuredInheritanceMode)) {
+                throw new IllegalArgumentException(String.format(
+                        "Invalid %s value '%s'. Supported values are: %s, %s, %s, %s",
+                        Constants.INHERITANCE_MODE,
+                        configuredInheritanceMode,
+                        Constants.INHERITANCE_MODE_NONE,
+                        Constants.INHERITANCE_MODE_SEALED,
+                        Constants.INHERITANCE_MODE_ABSTRACT,
+                        Constants.INHERITANCE_MODE_COMPOSITION));
+            }
+            inheritanceMode = configuredInheritanceMode;
+        }
+
+        if (Constants.JAXRS_SPEC.equals(library) && Constants.INHERITANCE_MODE_SEALED.equals(inheritanceMode)) {
+            throw new IllegalArgumentException(String.format(
+                    "Library '%s' does not support inheritanceMode '%s'. Use '%s', '%s', or '%s'.",
+                    Constants.JAXRS_SPEC,
+                    Constants.INHERITANCE_MODE_SEALED,
+                    Constants.INHERITANCE_MODE_NONE,
+                    Constants.INHERITANCE_MODE_ABSTRACT,
+                    Constants.INHERITANCE_MODE_COMPOSITION));
+        }
+        additionalProperties.put(Constants.INHERITANCE_MODE, inheritanceMode);
+        additionalProperties.put(Constants.X_INHERITANCE_MODE_NONE, Constants.INHERITANCE_MODE_NONE.equals(inheritanceMode));
+        additionalProperties.put(Constants.X_INHERITANCE_MODE_SEALED, Constants.INHERITANCE_MODE_SEALED.equals(inheritanceMode));
+        additionalProperties.put(Constants.X_INHERITANCE_MODE_ABSTRACT, Constants.INHERITANCE_MODE_ABSTRACT.equals(inheritanceMode));
+        additionalProperties.put(Constants.X_INHERITANCE_MODE_COMPOSITION, Constants.INHERITANCE_MODE_COMPOSITION.equals(inheritanceMode));
+
         if (isKtor()) {
             typeMapping.put("date-time", "kotlin.String");
             typeMapping.put("DateTime", "kotlin.String");
@@ -436,12 +479,36 @@ public static class Constants {
         public static final String USE_TAGS_DESC = "use tags for creating interface and controller classnames.";
         public static final String DELEGATE_PATTERN = "delegatePattern";
         public static final String DELEGATE_PATTERN_DESC = "Whether to generate the server files using the delegate pattern. This option is currently supported only when using ktor library.";
+        public static final String INHERITANCE_MODE = "inheritanceMode";
+        public static final String INHERITANCE_MODE_DESC = "Strategy for model inheritance generation. Values: none, sealed, abstract, composition.";
+        public static final String INHERITANCE_MODE_NONE = "none";
+        public static final String INHERITANCE_MODE_SEALED = "sealed";
+        public static final String INHERITANCE_MODE_ABSTRACT = "abstract";
+        public static final String INHERITANCE_MODE_COMPOSITION = "composition";
+        public static final String X_INHERITANCE_MODE_NONE = "x-inheritance-mode-none";
+        public static final String X_INHERITANCE_MODE_SEALED = "x-inheritance-mode-sealed";
+        public static final String X_INHERITANCE_MODE_ABSTRACT = "x-inheritance-mode-abstract";
+        public static final String X_INHERITANCE_MODE_COMPOSITION = "x-inheritance-mode-composition";
     }
 
     @Override
     public Map<String, ModelsMap> postProcessAllModels(Map<String, ModelsMap> objs) {
         objs = super.postProcessAllModels(objs);
 
+        if (Constants.INHERITANCE_MODE_NONE.equals(inheritanceMode)) {
+            flattenInheritanceForNoneMode(objs);
+            return objs;
+        }
+
+        if (Constants.INHERITANCE_MODE_COMPOSITION.equals(inheritanceMode)) {
+            applyCompositionMode(objs);
+            return objs;
+        }
+
+        if (!isInheritancePostProcessingEnabled()) {
+            return objs;
+        }
+
         // For libraries that use Jackson, set up parent-child relationships for discriminator children
         // This enables proper polymorphism support with @JsonTypeInfo and @JsonSubTypes annotations
         if (usesJacksonSerialization()) {
@@ -920,4 +987,112 @@ private static String getCommonPath(String path1, String path2) {
         }
         return builder.toString();
     }
+
+    private static String defaultInheritanceModeForLibrary(String currentLibrary) {
+        return Constants.JAXRS_SPEC.equals(currentLibrary)
+                ? Constants.INHERITANCE_MODE_ABSTRACT
+                : Constants.INHERITANCE_MODE_SEALED;
+    }
+
+    private static boolean isValidInheritanceMode(String value) {
+        return Constants.INHERITANCE_MODE_NONE.equals(value)
+                || Constants.INHERITANCE_MODE_SEALED.equals(value)
+                || Constants.INHERITANCE_MODE_ABSTRACT.equals(value)
+                || Constants.INHERITANCE_MODE_COMPOSITION.equals(value);
+    }
+
+    private static void flattenInheritanceForNoneMode(Map<String, ModelsMap> objs) {
+        for (ModelsMap modelsMap : objs.values()) {
+            for (ModelMap modelMap : modelsMap.getModels()) {
+                CodegenModel model = modelMap.getModel();
+
+                model.setDiscriminator(null);
+                model.setParent(null);
+                model.getVendorExtensions().remove("x-parent-ctor-args");
+                model.getVendorExtensions().remove("x-discriminator-has-parent-properties");
+                model.getVendorExtensions().remove("x-discriminator-visible-true");
+
+                if (model.interfaces != null) {
+                    model.interfaces.clear();
+                }
+
+                for (CodegenProperty prop : model.getAllVars()) {
+                    prop.isInherited = false;
+                }
+                for (CodegenProperty prop : model.getVars()) {
+                    prop.isInherited = false;
+                }
+                for (CodegenProperty prop : model.getRequiredVars()) {
+                    prop.isInherited = false;
+                }
+                for (CodegenProperty prop : model.getOptionalVars()) {
+                    prop.isInherited = false;
+                }
+            }
+        }
+    }
+
+    private static void applyCompositionMode(Map<String, ModelsMap> objs) {
+        Set<String> discriminatorOwners = new HashSet<>();
+        for (ModelsMap modelsMap : objs.values()) {
+            for (ModelMap modelMap : modelsMap.getModels()) {
+                CodegenModel model = modelMap.getModel();
+                if (model.getDiscriminator() != null
+                        && model.getDiscriminator().getMappedModels() != null
+                        && !model.getDiscriminator().getMappedModels().isEmpty()) {
+                    discriminatorOwners.add(model.getClassname());
+                }
+            }
+        }
+
+        flattenInheritanceForNoneMode(objs);
+
+        for (ModelsMap modelsMap : objs.values()) {
+            for (ModelMap modelMap : modelsMap.getModels()) {
+                CodegenModel model = modelMap.getModel();
+                if (discriminatorOwners.contains(model.getClassname())) {
+                    replaceWithCompositionWrapper(model);
+                }
+            }
+        }
+    }
+
+    private static void replaceWithCompositionWrapper(CodegenModel model) {
+        CodegenProperty wrapperValue = new CodegenProperty();
+        wrapperValue.baseName = "value";
+        wrapperValue.name = "value";
+        wrapperValue.dataType = "kotlin.Any";
+        wrapperValue.datatypeWithEnum = "kotlin.Any";
+        wrapperValue.required = true;
+        wrapperValue.isNullable = false;
+        wrapperValue.isReadOnly = false;
+
+        model.getVars().clear();
+        model.getAllVars().clear();
+        model.getRequiredVars().clear();
+        model.getOptionalVars().clear();
+        model.getMandatory().clear();
+        model.getAllMandatory().clear();
+        model.oneOf.clear();
+        model.anyOf.clear();
+        model.allOf.clear();
+
+        model.getVars().add(wrapperValue);
+        model.getAllVars().add(wrapperValue);
+        model.getRequiredVars().add(wrapperValue);
+        model.getMandatory().add("value");
+        model.getAllMandatory().add("value");
+
+        model.hasVars = true;
+        model.hasRequired = true;
+        model.hasOptional = false;
+        model.emptyVars = false;
+        model.getVendorExtensions().put("x-composition-wrapper", true);
+    }
+
+    private boolean isInheritancePostProcessingEnabled() {
+        // `none` and `composition` are handled in dedicated short-circuit paths.
+        return !Constants.INHERITANCE_MODE_NONE.equals(inheritanceMode)
+                && !Constants.INHERITANCE_MODE_COMPOSITION.equals(inheritanceMode);
+    }
 }

modules/openapi-generator/src/main/resources/kotlin-server/data_class.mustache

@@ -85,7 +85,7 @@ import java.io.Serializable
 {{#discriminator}}
 {{>typeInfoAnnotation}}
 {{#vendorExtensions.x-discriminator-has-parent-properties}}
-sealed class {{classname}}(
+{{#x-inheritance-mode-abstract}}abstract class{{/x-inheritance-mode-abstract}}{{^x-inheritance-mode-abstract}}sealed class{{/x-inheritance-mode-abstract}} {{classname}}(
 {{#requiredVars}}
 {{>data_class_sealed_var}}{{^-last}},
 {{/-last}}{{/requiredVars}}{{#hasRequired}}{{#hasOptional}},
@@ -94,7 +94,7 @@ sealed class {{classname}}(
 )
 {{/vendorExtensions.x-discriminator-has-parent-properties}}
 {{^vendorExtensions.x-discriminator-has-parent-properties}}
-sealed class {{classname}}
+{{#x-inheritance-mode-abstract}}abstract class{{/x-inheritance-mode-abstract}}{{^x-inheritance-mode-abstract}}sealed class{{/x-inheritance-mode-abstract}} {{classname}}
 {{/vendorExtensions.x-discriminator-has-parent-properties}}
 {{/discriminator}}
 {{^discriminator}}

modules/openapi-generator/src/main/resources/kotlin-server/libraries/jaxrs-spec/data_class.mustache

@@ -29,22 +29,28 @@ import java.io.Serializable
 {{/isDeprecated}}
 {{>additionalModelTypeAnnotations}}
 
-{{#nonPublicApi}}internal {{/nonPublicApi}}{{#discriminator}}interface{{/discriminator}}{{^discriminator}}data class{{/discriminator}} {{classname}}{{^discriminator}} (
+{{#nonPublicApi}}internal {{/nonPublicApi}}{{#discriminator}}{{#x-inheritance-mode-abstract}}abstract class{{/x-inheritance-mode-abstract}}{{^x-inheritance-mode-abstract}}interface{{/x-inheritance-mode-abstract}}{{/discriminator}}{{^discriminator}}data class{{/discriminator}} {{classname}}{{^discriminator}} (
 
 {{#allVars}}
 {{#required}}{{>data_class_req_var}}{{/required}}{{^required}}{{>data_class_opt_var}}{{/required}}{{^-last}},{{/-last}}
 
 {{/allVars}}
-){{/discriminator}}{{#parent}}{{^serializableModel}}{{^parcelizeModels}} : {{{parent}}}{{#isMap}}(){{/isMap}}{{#isArray}}(){{/isArray}}{{/parcelizeModels}}{{/serializableModel}}{{/parent}}{{#parent}}{{#serializableModel}}{{^parcelizeModels}} : {{{parent}}}{{#isMap}}(){{/isMap}}{{#isArray}}(){{/isArray}}, Serializable{{/parcelizeModels}}{{/serializableModel}}{{/parent}}{{#parent}}{{^serializableModel}}{{#parcelizeModels}} : {{{parent}}}{{#isMap}}(){{/isMap}}{{#isArray}}(){{/isArray}}, Parcelable{{/parcelizeModels}}{{/serializableModel}}{{/parent}}{{#parent}}{{#serializableModel}}{{#parcelizeModels}} : {{{parent}}}{{#isMap}}(){{/isMap}}{{#isArray}}(){{/isArray}}, Serializable, Parcelable{{/parcelizeModels}}{{/serializableModel}}{{/parent}}{{^parent}}{{#serializableModel}}{{^parcelizeModels}} : Serializable{{/parcelizeModels}}{{/serializableModel}}{{/parent}}{{^parent}}{{^serializableModel}}{{#parcelizeModels}} : Parcelable{{/parcelizeModels}}{{/serializableModel}}{{/parent}}{{^parent}}{{#serializableModel}}{{#parcelizeModels}} : Serializable, Parcelable{{/parcelizeModels}}{{/serializableModel}}{{/parent}}{{#vendorExtensions.x-has-data-class-body}} {
+){{/discriminator}}{{#discriminator}}{{#x-inheritance-mode-abstract}}(
+
+{{#allVars}}
+{{#required}}{{>data_class_sealed_var}}{{/required}}{{^required}}{{>data_class_sealed_var}}{{/required}}{{^-last}},{{/-last}}
+
+{{/allVars}}
+){{/x-inheritance-mode-abstract}}{{/discriminator}}{{#parent}}{{^serializableModel}}{{^parcelizeModels}} : {{{parent}}}{{#vendorExtensions.x-parent-ctor-args}}({{{.}}}){{/vendorExtensions.x-parent-ctor-args}}{{^vendorExtensions.x-parent-ctor-args}}{{#isMap}}(){{/isMap}}{{#isArray}}(){{/isArray}}{{/vendorExtensions.x-parent-ctor-args}}{{/parcelizeModels}}{{/serializableModel}}{{/parent}}{{#parent}}{{#serializableModel}}{{^parcelizeModels}} : {{{parent}}}{{#isMap}}(){{/isMap}}{{#isArray}}(){{/isArray}}, Serializable{{/parcelizeModels}}{{/serializableModel}}{{/parent}}{{#parent}}{{^serializableModel}}{{#parcelizeModels}} : {{{parent}}}{{#isMap}}(){{/isMap}}{{#isArray}}(){{/isArray}}, Parcelable{{/parcelizeModels}}{{/serializableModel}}{{/parent}}{{#parent}}{{#serializableModel}}{{#parcelizeModels}} : {{{parent}}}{{#isMap}}(){{/isMap}}{{#isArray}}(){{/isArray}}, Serializable, Parcelable{{/parcelizeModels}}{{/serializableModel}}{{/parent}}{{^parent}}{{#serializableModel}}{{^parcelizeModels}} : Serializable{{/parcelizeModels}}{{/serializableModel}}{{/parent}}{{^parent}}{{^serializableModel}}{{#parcelizeModels}} : Parcelable{{/parcelizeModels}}{{/serializableModel}}{{/parent}}{{^parent}}{{#serializableModel}}{{#parcelizeModels}} : Serializable, Parcelable{{/parcelizeModels}}{{/serializableModel}}{{/parent}}{{#vendorExtensions.x-has-data-class-body}} {
 {{/vendorExtensions.x-has-data-class-body}}
 {{#serializableModel}}
     {{#nonPublicApi}}internal {{/nonPublicApi}}companion object {
         private const val serialVersionUID: Long = 123
     }
 {{/serializableModel}}
-{{#discriminator}}{{#vars}}{{#required}}
+{{#discriminator}}{{^x-inheritance-mode-abstract}}{{#vars}}{{#required}}
 {{>interface_req_var}}{{/required}}{{^required}}
-{{>interface_opt_var}}{{/required}}{{/vars}}{{/discriminator}}
+{{>interface_opt_var}}{{/required}}{{/vars}}{{/x-inheritance-mode-abstract}}{{/discriminator}}
 {{#hasEnums}}
 {{#vars}}
 {{#isEnum}}

modules/openapi-generator/src/main/resources/kotlin-server/libraries/jaxrs-spec/data_class_opt_var.mustache

@@ -3,4 +3,4 @@
 {{/description}}
 
     @JsonProperty("{{#lambda.escapeDollar}}{{baseName}}{{/lambda.escapeDollar}}")
-{{#useBeanValidation}}{{>beanValidation}}{{>beanValidationModel}}{{/useBeanValidation}}    {{>modelMutable}} {{{name}}}: {{#isEnum}}{{classname}}.{{nameInPascalCase}}{{/isEnum}}{{^isEnum}}{{{dataType}}}{{/isEnum}}? = {{{defaultValue}}}{{^defaultValue}}null{{/defaultValue}}
+{{#useBeanValidation}}{{>beanValidation}}{{>beanValidationModel}}{{/useBeanValidation}}    {{#isInherited}}override {{/isInherited}}{{>modelMutable}} {{{name}}}: {{#isEnum}}{{classname}}.{{nameInPascalCase}}{{/isEnum}}{{^isEnum}}{{{dataType}}}{{/isEnum}}? = {{{defaultValue}}}{{^defaultValue}}null{{/defaultValue}}

modules/openapi-generator/src/main/resources/kotlin-server/libraries/jaxrs-spec/data_class_req_var.mustache

@@ -3,4 +3,4 @@
 {{/description}}
 
     @JsonProperty("{{#lambda.escapeDollar}}{{baseName}}{{/lambda.escapeDollar}}")
-{{#useBeanValidation}}{{>beanValidation}}{{>beanValidationModel}}{{/useBeanValidation}}    {{>modelMutable}} {{{name}}}: {{#isEnum}}{{classname}}.{{nameInPascalCase}}{{/isEnum}}{{^isEnum}}{{{dataType}}}{{/isEnum}}
+{{#useBeanValidation}}{{>beanValidation}}{{>beanValidationModel}}{{/useBeanValidation}}    {{#isInherited}}override {{/isInherited}}{{>modelMutable}} {{{name}}}: {{#isEnum}}{{classname}}.{{nameInPascalCase}}{{/isEnum}}{{^isEnum}}{{{dataType}}}{{/isEnum}}