[KOTLIN-SPRING] Add oneOf sealed interface support with discriminator

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
Co-Authored-By: brohacz <brohacz@users.noreply.github.com>
Co-Authored-By: KZwolski <KZwolski@users.noreply.github.com>

Author: 4 people

.github/workflows/samples-kotlin-server-jdk17.yaml

@@ -4,6 +4,7 @@ on:
   push:
     paths:
       - 'samples/server/others/kotlin-server/**'
+      - 'samples/server/others/kotlin-springboot/**'
       - 'samples/server/petstore/kotlin-springboot-3*/**'
       - 'samples/server/petstore/kotlin-server/**'
       - 'samples/server/petstore/kotlin-server-modelMutable/**'
@@ -18,6 +19,7 @@ on:
   pull_request:
     paths:
       - 'samples/server/others/kotlin-server/**'
+      - 'samples/server/others/kotlin-springboot/**'
       - 'samples/server/petstore/kotlin-springboot-3*/**'
       - 'samples/server/petstore/kotlin-server/**'
       - 'samples/server/petstore/kotlin-server-modelMutable/**'
@@ -42,6 +44,9 @@ jobs:
       matrix:
         sample:
           # server
+          - samples/server/others/kotlin-springboot/oneOf-discriminator
+          - samples/server/others/kotlin-springboot/oneOf-discriminator-const
+          - samples/server/others/kotlin-springboot/oneOf-enum-discriminator
           - samples/server/others/kotlin-server/polymorphism-allof-and-discriminator
           - samples/server/others/kotlin-server/polymorphism-and-discriminator-disabled-jackson-fix
           - samples/server/others/kotlin-server/polymorphism-and-discriminator

.github/workflows/samples-kotlin-server-jdk21.yaml

@@ -4,11 +4,13 @@ on:
   push:
     paths:
       - 'samples/server/others/kotlin-server/**'
+      - 'samples/server/others/kotlin-springboot/**'
       - 'samples/server/petstore/kotlin-server/**'
       - 'samples/server/petstore/kotlin-server-required-and-nullable-properties/**'
   pull_request:
     paths:
       - 'samples/server/others/kotlin-server/**'
+      - 'samples/server/others/kotlin-springboot/**'
       - 'samples/server/petstore/kotlin-server/**'
       - 'samples/server/petstore/kotlin-server-required-and-nullable-properties/**'
 
@@ -23,6 +25,9 @@ jobs:
       fail-fast: false
       matrix:
         sample:
+          - samples/server/others/kotlin-springboot/oneOf-discriminator
+          - samples/server/others/kotlin-springboot/oneOf-discriminator-const
+          - samples/server/others/kotlin-springboot/oneOf-enum-discriminator
           - samples/server/others/kotlin-server/polymorphism-allof-and-discriminator
           - samples/server/others/kotlin-server/polymorphism-and-discriminator-disabled-jackson-fix
           - samples/server/others/kotlin-server/polymorphism-and-discriminator

bin/configs/kotlin-spring-boot-oneof-discriminator-const.yaml

@@ -0,0 +1,11 @@
+generatorName: kotlin-spring
+outputDir: samples/server/others/kotlin-springboot/oneOf-discriminator-const
+library: spring-boot
+inputSpec: modules/openapi-generator/src/test/resources/3_1/polymorphism-and-discriminator.yaml
+templateDir: modules/openapi-generator/src/main/resources/kotlin-spring
+additionalProperties:
+  documentationProvider: none
+  annotationLibrary: none
+  useSwaggerUI: "false"
+  interfaceOnly: "true"
+  useSpringBoot3: "true"

bin/configs/kotlin-spring-boot-oneof-discriminator.yaml

@@ -0,0 +1,11 @@
+generatorName: kotlin-spring
+outputDir: samples/server/others/kotlin-springboot/oneOf-discriminator
+library: spring-boot
+inputSpec: modules/openapi-generator/src/test/resources/3_0/kotlin/polymorphism-oneof-discriminator.yaml
+templateDir: modules/openapi-generator/src/main/resources/kotlin-spring
+additionalProperties:
+  documentationProvider: none
+  annotationLibrary: none
+  useSwaggerUI: "false"
+  interfaceOnly: "true"
+  useSpringBoot3: "true"

bin/configs/kotlin-spring-boot-oneof-enum-discriminator.yaml

@@ -0,0 +1,11 @@
+generatorName: kotlin-spring
+outputDir: samples/server/others/kotlin-springboot/oneOf-enum-discriminator
+library: spring-boot
+inputSpec: modules/openapi-generator/src/test/resources/3_0/kotlin/polymorphism-oneof-enum-discriminator.yaml
+templateDir: modules/openapi-generator/src/main/resources/kotlin-spring
+additionalProperties:
+  documentationProvider: none
+  annotationLibrary: none
+  useSwaggerUI: "false"
+  interfaceOnly: "true"
+  useSpringBoot3: "true"

docs/generators/kotlin-spring.md

@@ -313,7 +313,7 @@ These options may be applied as additional-properties (cli) or configOptions (pl
 |Union|✗|OAS3
 |allOf|✗|OAS2,OAS3
 |anyOf|✗|OAS3
-|oneOf|✗|OAS3
+|oneOf|✓|OAS3
 |not|✗|OAS3
 
 ### Security Feature

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

@@ -421,10 +421,28 @@ public String modelFileFolder() {
     }
 
     @Override
+    @SuppressWarnings("unchecked")
     public Map<String, ModelsMap> postProcessAllModels(Map<String, ModelsMap> objs) {
         objs = super.postProcessAllModels(objs);
         objs = super.updateAllModels(objs);
 
+        // Bridge x-implements (set by oneOf pipeline) into x-kotlin-implements (read by Kotlin templates)
+        for (ModelsMap modelsAttrs : objs.values()) {
+            for (ModelMap mo : modelsAttrs.getModels()) {
+                CodegenModel cm = mo.getModel();
+                List<String> xImplements = (List<String>) cm.getVendorExtensions().get(CodegenConstants.X_IMPLEMENTS);
+                if (xImplements != null && !xImplements.isEmpty()) {
+                    List<String> kotlinImplements = (List<String>) cm.getVendorExtensions()
+                            .computeIfAbsent(VendorExtension.X_KOTLIN_IMPLEMENTS.getName(), k -> new ArrayList<>());
+                    for (String iface : xImplements) {
+                        if (!kotlinImplements.contains(iface)) {
+                            kotlinImplements.add(iface);
+                        }
+                    }
+                }
+            }
+        }
+
         if (!additionalModelTypeAnnotations.isEmpty()) {
             for (String modelName : objs.keySet()) {
                 Map<String, Object> models = (Map<String, Object>) objs.get(modelName);

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

@@ -49,6 +49,7 @@
 import java.util.*;
 import java.util.regex.Matcher;
 import java.util.stream.Collectors;
+import java.util.stream.Stream;
 
 import static org.openapitools.codegen.utils.CamelizeOption.LOWERCASE_FIRST_LETTER;
 import static org.openapitools.codegen.utils.StringUtils.camelize;
@@ -224,7 +225,8 @@ public KotlinSpringServerCodegen() {
                         GlobalFeature.ParameterStyling
                 )
                 .includeSchemaSupportFeatures(
-                        SchemaSupportFeature.Polymorphism
+                        SchemaSupportFeature.Polymorphism,
+                        SchemaSupportFeature.oneOf
                 )
                 .includeParameterFeatures(
                         ParameterFeature.Cookie
@@ -233,6 +235,9 @@ public KotlinSpringServerCodegen() {
 
         reservedWords.addAll(VARIABLE_RESERVED_WORDS);
 
+        // Enable oneOf interface generation (mirrors SpringCodegen behavior)
+        useOneOfInterfaces = true;
+
         outputFolder = "generated-code/kotlin-spring";
         embeddedTemplateDir = templateDir = "kotlin-spring";
 
@@ -1328,10 +1333,50 @@ public void postProcessModelProperty(CodegenModel model, CodegenProperty propert
         }
     }
 
+    @Override
+    public void addImportsToOneOfInterface(List<Map<String, String>> imports) {
+        if (additionalProperties.containsKey("jackson")) {
+            for (String i : Arrays.asList("JsonSubTypes", "JsonTypeInfo", "JsonIgnoreProperties")) {
+                Map<String, String> oneImport = new HashMap<>();
+                oneImport.put("import", importMapping.get(i));
+                if (!imports.contains(oneImport)) {
+                    imports.add(oneImport);
+                }
+            }
+        }
+    }
+
     @Override
     public Map<String, ModelsMap> postProcessAllModels(Map<String, ModelsMap> objs) {
         objs = super.postProcessAllModels(objs);
 
+        Map<String, CodegenModel> allModelsMap = getAllModels(objs);
+
+        // For each oneOf interface with a discriminator, mark the discriminator property
+        // as inherited in each subtype and set its default value from the discriminator mapping
+        for (CodegenModel cm : allModelsMap.values()) {
+            if (Boolean.TRUE.equals(cm.vendorExtensions.get(CodegenConstants.X_IS_ONE_OF_INTERFACE))
+                    && cm.discriminator != null) {
+                String discrimBaseName = cm.discriminator.getPropertyBaseName();
+                String discrimType = cm.discriminator.getPropertyType();
+                boolean isEnumDiscriminator = cm.discriminator.getIsEnum();
+
+                // Build child name -> mapping name lookup from discriminator mappings
+                Map<String, String> childToMappingName = new HashMap<>();
+                for (CodegenDiscriminator.MappedModel mm : cm.discriminator.getMappedModels()) {
+                    childToMappingName.put(mm.getModelName(), mm.getMappingName());
+                }
+
+                for (String childName : cm.oneOf) {
+                    CodegenModel child = allModelsMap.get(childName);
+                    if (child != null) {
+                        String mappingName = childToMappingName.get(childName);
+                        markPropertyAsInherited(child, discrimBaseName, discrimType, mappingName, isEnumDiscriminator);
+                    }
+                }
+            }
+        }
+
         if (substituteGenericPagedModel && !pagedModelRegistry.isEmpty()) {
             if (getAnnotationLibrary() == AnnotationLibrary.NONE) {
                 // No @ApiResponse annotations are generated when annotationLibrary=none,
@@ -1375,6 +1420,47 @@ public Map<String, ModelsMap> postProcessAllModels(Map<String, ModelsMap> objs)
         return objs;
     }
 
+    /**
+     * Marks the discriminator property as inherited on a subtype and sets its default value
+     * from the discriminator mapping, so the constructor has the correct default.
+     */
+    private void markPropertyAsInherited(CodegenModel model, String baseName, String dataType,
+                                         String discriminatorValue, boolean isEnumDiscriminator) {
+        Stream.of(model.vars, model.requiredVars, model.optionalVars, model.allVars)
+                .flatMap(List::stream)
+                .filter(p -> baseName.equals(p.baseName))
+                .forEach(p -> {
+                    p.isInherited = true;
+                    // Discriminator properties must match the parent interface type (non-null, required)
+                    if (dataType != null) {
+                        p.dataType = dataType;
+                        p.datatypeWithEnum = dataType;
+                        p.isNullable = false;
+                        p.required = true;
+                    }
+                    if (discriminatorValue != null) {
+                        if (isEnumDiscriminator) {
+                            p.defaultValue = dataType + "." + toEnumVarName(discriminatorValue, dataType);
+                        } else {
+                            p.defaultValue = "\"" + escapeText(discriminatorValue) + "\"";
+                        }
+                    }
+                });
+        // Move discriminator property from optionalVars to requiredVars if needed.
+        // Safe to modify optionalVars here — the stream above has fully completed.
+        if (dataType != null) {
+            model.optionalVars.stream()
+                    .filter(p -> baseName.equals(p.baseName))
+                    .findFirst()
+                    .ifPresent(p -> {
+                        model.optionalVars.remove(p);
+                        model.requiredVars.add(p);
+                    });
+            model.hasRequired = !model.requiredVars.isEmpty();
+            model.hasOptional = !model.optionalVars.isEmpty();
+        }
+    }
+
     @Override
     public ModelsMap postProcessModelsEnum(ModelsMap objs) {
         objs = super.postProcessModelsEnum(objs);

modules/openapi-generator/src/main/resources/kotlin-spring/dataClass.mustache

@@ -1,8 +1,11 @@
 /**
  * {{{description}}}
-{{#vars}}
+{{#requiredVars}}
+ * @param {{name}} {{{description}}}
+{{/requiredVars}}
+{{#optionalVars}}
  * @param {{name}} {{{description}}}
-{{/vars}}
+{{/optionalVars}}
  */{{#discriminator}}
 {{>typeInfoAnnotation}}{{/discriminator}}
 {{#additionalModelTypeAnnotations}}
@@ -54,7 +57,7 @@
             @JsonCreator
             fun forValue(value: {{#isContainer}}{{#items}}{{{dataType}}}{{/items}}{{/isContainer}}{{^isContainer}}{{{dataType}}}{{/isContainer}}): {{{nameInPascalCase}}} {
                 return values().firstOrNull{it -> it.value == value}
-                    ?: throw IllegalArgumentException("Unexpected value '$value' for enum '{{classname}}'")
+                    ?: throw IllegalArgumentException("Unexpected value '$value' for enum '{{nameInPascalCase}}'")
             }
         }
     }

modules/openapi-generator/src/main/resources/kotlin-spring/model.mustache

@@ -23,6 +23,6 @@ import io.swagger.annotations.ApiModelProperty
 
 {{#models}}
 {{#model}}
-{{#isEnum}}{{>enumClass}}{{/isEnum}}{{^isEnum}}{{>dataClass}}{{/isEnum}}
+{{#isEnum}}{{>enumClass}}{{/isEnum}}{{^isEnum}}{{#vendorExtensions.x-is-one-of-interface}}{{>oneof_interface}}{{/vendorExtensions.x-is-one-of-interface}}{{^vendorExtensions.x-is-one-of-interface}}{{>dataClass}}{{/vendorExtensions.x-is-one-of-interface}}{{/isEnum}}
 {{/model}}
 {{/models}}