[kotlin] implement serializable data classes (#8317)

Author: LucasKuhlemann

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

@@ -208,6 +208,7 @@ public KotlinSpringServerCodegen() {
                 " (contexts) added to single project.", beanQualifiers);
         addSwitch(USE_SPRING_BOOT3, "Generate code and provide dependencies for use with Spring Boot 3.x. (Use jakarta instead of javax in imports). Enabling this option will also enable `useJakartaEe`.", useSpringBoot3);
         addSwitch(APPEND_REQUEST_TO_HANDLER, "Append ServerHttpRequest to handler method for getting request stuff", false);
+        addSwitch(CodegenConstants.SERIALIZABLE_MODEL, "toggle \"implements Serializable\" for generated models", null);
         supportedLibraries.put(SPRING_BOOT, "Spring-boot Server application.");
         supportedLibraries.put(SPRING_CLOUD_LIBRARY,
                 "Spring-Cloud-Feign client with Spring-Boot auto-configured settings.");

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

@@ -14,7 +14,7 @@
 {{/-last}}{{/requiredVars}}{{#hasRequired}}{{#hasOptional}},
 {{/hasOptional}}{{/hasRequired}}{{#optionalVars}}{{>dataClassOptVar}}{{^-last}},
 {{/-last}}{{/optionalVars}}
-) {{/discriminator}}{{#parent}}: {{{.}}}{{/parent}}{
+) {{/discriminator}}{{#parent}}: {{{.}}}{{#serializableModel}}, Serializable{{/serializableModel}}{{/parent}}{{#serializableModel}}: Serializable{{/serializableModel}} {
 {{#discriminator}}
     {{#requiredVars}}
         {{>interfaceReqVar}}
@@ -33,4 +33,9 @@
         @JsonProperty({{{value}}}) {{{name}}}({{{value}}}){{^-last}},{{/-last}}{{/enumVars}}{{/allowableValues}}
     }
 {{/isEnum}}{{/vars}}{{/hasEnums}}
+{{#serializableModel}}
+    companion object {
+        private const val serialVersionUID: kotlin.Long = 1
+    }
+{{/serializableModel}}
 }

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

@@ -3,6 +3,9 @@ package {{package}}
 import java.util.Objects
 {{#imports}}import {{import}}
 {{/imports}}
+{{#serializableModel}}
+import java.io.Serializable
+{{/serializableModel}}
 {{#useBeanValidation}}
 import {{javaxPackage}}.validation.constraints.DecimalMax
 import {{javaxPackage}}.validation.constraints.DecimalMin

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

@@ -115,6 +115,7 @@ public void testSettersForConfigValues() throws Exception {
         codegen.setServiceImplementation(true);
         codegen.setUseBeanValidation(false);
         codegen.setReactive(false);
+        codegen.setSerializableModel(true);
         codegen.processOpts();
 
         Assert.assertEquals(codegen.modelPackage(), "xx.yyyyyyyy.model");
@@ -137,6 +138,8 @@ public void testSettersForConfigValues() throws Exception {
         Assert.assertEquals(codegen.additionalProperties().get(KotlinSpringServerCodegen.USE_BEANVALIDATION), false);
         Assert.assertFalse(codegen.isReactive());
         Assert.assertEquals(codegen.additionalProperties().get(KotlinSpringServerCodegen.REACTIVE), false);
+        Assert.assertTrue(codegen.isSerializableModel());
+        Assert.assertEquals(codegen.additionalProperties().get(CodegenConstants.SERIALIZABLE_MODEL), true);
     }
 
     @Test
@@ -678,4 +681,35 @@ public void givenMultipartForm_whenGenerateReactiveServer_thenParameterAreCreate
                            "@Parameter(description = \"image to upload\") @Valid @RequestPart(\"image\", required = false) image: org.springframework.core.io.Resource?");
 
     }
-}
+
+    @Test
+    public void generateSerializableModel() throws Exception {
+        File output = Files.createTempDirectory("test").toFile().getCanonicalFile();
+        output.deleteOnExit();
+        String outputPath = output.getAbsolutePath().replace('\\', '/');
+
+        KotlinSpringServerCodegen codegen = new KotlinSpringServerCodegen();
+        codegen.setOutputDir(output.getAbsolutePath());
+        codegen.additionalProperties().put(CodegenConstants.SERIALIZABLE_MODEL, true);
+
+        ClientOptInput input = new ClientOptInput()
+                .openAPI(TestUtils.parseSpec("src/test/resources/3_0/kotlin/petstore.yaml"))
+                .config(codegen);
+        DefaultGenerator generator = new DefaultGenerator();
+
+        generator.setGeneratorPropertyDefault(CodegenConstants.MODELS, "true");
+        generator.setGeneratorPropertyDefault(CodegenConstants.MODEL_TESTS, "false");
+        generator.setGeneratorPropertyDefault(CodegenConstants.MODEL_DOCS, "false");
+        generator.setGeneratorPropertyDefault(CodegenConstants.APIS, "false");
+        generator.setGeneratorPropertyDefault(CodegenConstants.SUPPORTING_FILES, "false");
+
+        generator.opts(input).generate();
+
+        assertFileContains(
+                Paths.get(outputPath + "/src/main/kotlin/org/openapitools/model/Pet.kt"),
+                "import java.io.Serializable",
+                ") : Serializable {",
+                "private const val serialVersionUID: kotlin.Long = 1"
+        );
+    }
+}