Add support for oneOf with discriminator when using kotlinx.serialization (#22373)

* Generate wrappers for oneOf with discriminator when using kotlinx.serialization

* Add spec with oneOf using discriminator

* Add config to generate samples

* Generate samples

* Update samples

* Change naming of wrapper classes

* Fix empty model test

* Update GH workflow with new samples

Author: diastremskii

.github/workflows/samples-kotlin-client.yaml

@@ -72,6 +72,7 @@ jobs:
           - samples/client/others/kotlin-jvm-okhttp-path-comments
           - samples/client/others/kotlin-integer-enum
           - samples/client/petstore/kotlin-allOf-discriminator-kotlinx-serialization
+          - samples/client/others/kotlin-oneOf-discriminator-kotlinx-serialization
     steps:
       - uses: actions/checkout@v5
       - uses: actions/setup-java@v5

bin/configs/kotlin-oneOf-discriminator-kotlinx-serialization.yaml

@@ -0,0 +1,12 @@
+generatorName: kotlin
+outputDir: samples/client/others/kotlin-oneOf-discriminator-kotlinx-serialization
+inputSpec: modules/openapi-generator/src/test/resources/3_0/kotlin/polymorphism-oneof-discriminator.yaml
+templateDir: modules/openapi-generator/src/main/resources/kotlin-client
+additionalProperties:
+  artifactId: kotlin-oneOf-discriminator
+  serializableModel: "false"
+  dateLibrary: java8
+  library: jvm-retrofit2
+  enumUnknownDefaultCase: true
+  serializationLibrary: kotlinx_serialization
+  generateOneOfAnyOfWrappers: true

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

@@ -20,6 +20,7 @@
 import com.fasterxml.jackson.databind.node.ArrayNode;
 import com.google.common.collect.ImmutableMap;
 import com.samskivert.mustache.Mustache;
+import com.samskivert.mustache.Template;
 import io.swagger.v3.oas.models.media.Schema;
 import io.swagger.v3.oas.models.media.StringSchema;
 import lombok.Getter;
@@ -35,6 +36,9 @@
 import org.slf4j.LoggerFactory;
 
 import java.io.File;
+import java.io.IOException;
+import java.io.StringWriter;
+import java.io.Writer;
 import java.util.*;
 import java.util.function.Function;
 import java.util.regex.Pattern;
@@ -1172,4 +1176,15 @@ protected void doDataTypeAssignment(final String returnType, DataTypeAssigner da
             }
         }
     }
+
+    protected static abstract class CustomLambda implements Mustache.Lambda {
+        @Override
+        public void execute(Template.Fragment frag, Writer out) throws IOException {
+            final StringWriter tempWriter = new StringWriter();
+            frag.execute(tempWriter);
+            out.write(formatFragment(tempWriter.toString()));
+        }
+
+        public abstract String formatFragment(String fragment);
+    }
 }

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

@@ -22,7 +22,6 @@
 import lombok.Setter;
 import org.apache.commons.lang3.StringUtils;
 import org.openapitools.codegen.*;
-import org.openapitools.codegen.meta.features.*;
 import org.openapitools.codegen.model.ModelMap;
 import org.openapitools.codegen.model.ModelsMap;
 import org.openapitools.codegen.model.OperationMap;
@@ -40,10 +39,8 @@
 import java.util.stream.Collectors;
 import java.util.stream.Stream;
 
-import com.samskivert.mustache.Mustache;
 import lombok.Getter;
 import lombok.Setter;
-import org.apache.commons.lang3.StringUtils;
 import org.openapitools.codegen.CliOption;
 import org.openapitools.codegen.CodegenConstants;
 import org.openapitools.codegen.CodegenModel;
@@ -60,14 +57,7 @@
 import org.openapitools.codegen.meta.features.SchemaSupportFeature;
 import org.openapitools.codegen.meta.features.SecurityFeature;
 import org.openapitools.codegen.meta.features.WireFormatFeature;
-import org.openapitools.codegen.model.ModelMap;
-import org.openapitools.codegen.model.ModelsMap;
-import org.openapitools.codegen.model.OperationMap;
-import org.openapitools.codegen.model.OperationsMap;
 import org.openapitools.codegen.templating.mustache.ReplaceAllLambda;
-import org.openapitools.codegen.utils.ProcessUtils;
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
 
 import static java.util.Collections.sort;
 
@@ -569,6 +559,7 @@ public void processOpts() {
         // as the parser interrupts that as a start of a multiline comment.
         // We replace paths like `/v1/foo/*` with `/v1/foo/<*>` to avoid this
         additionalProperties.put("sanitizePathComment", new ReplaceAllLambda("\\/\\*", "/<*>"));
+        additionalProperties.put("fnToOneOfWrapperName", new ToOneOfWrapperName());
     }
 
     private void processDateLibrary() {
@@ -974,11 +965,21 @@ public Map<String, ModelsMap> postProcessAllModels(Map<String, ModelsMap> objs)
                     if (discriminator == null) {
                         continue;
                     }
+
+                    // When using generateOneOfAnyOfWrappers and encountering oneOf, we keep discriminator properties,
+                    // because single entity can be referenced in multiple "parent" entities,
+                    // so discriminator for one might not be discriminator for another.
+                    boolean shouldKeepDiscriminatorField = generateOneOfAnyOfWrappers && cm.oneOf != null && !cm.oneOf.isEmpty();
+
+                    if (shouldKeepDiscriminatorField) {
+                        continue;
+                    }
+
                     // Remove discriminator property from the base class, it is not needed in the generated code
                     getAllVarProperties(cm).forEach(list -> list.removeIf(var -> var.name.equals(discriminator.getPropertyName())));
 
                     for (CodegenDiscriminator.MappedModel mappedModel : discriminator.getMappedModels()) {
-                        // Add the mapping name to additionalProperties.disciminatorValue
+                        // Add the mapping name to additionalProperties.discriminatorValue
                         // The mapping name is used to define SerializedName, which in result makes derived classes
                         // found by kotlinx-serialization during deserialization
                         CodegenProperty additionalProperties = mappedModel.getModel().getAdditionalProperties();
@@ -996,7 +997,6 @@ public Map<String, ModelsMap> postProcessAllModels(Map<String, ModelsMap> objs)
                             mappedModel.getModel().setHasVars(false);
                         }
                     }
-
                 }
             }
         }
@@ -1141,6 +1141,13 @@ private void adjustEnumRefDefault(CodegenParameter param) {
         param.defaultValue = type + "." + param.enumDefaultValue;
     }
 
+    private class ToOneOfWrapperName extends CustomLambda {
+        @Override
+        public String formatFragment(String fragment) {
+            return toModelName(StringUtils.lowerCase(fragment)) + "Wrapper";
+        }
+    }
+
     @Override
     public void postProcess() {
         System.out.println("################################################################################");

modules/openapi-generator/src/main/resources/kotlin-client/oneof_class.mustache

@@ -37,6 +37,28 @@ import kotlinx.serialization.builtins.serializer
 import kotlinx.serialization.encoding.Decoder
 import kotlinx.serialization.encoding.Encoder
 {{/enumUnknownDefaultCase}}
+{{^enumUnknownDefaultCase}}
+{{#generateOneOfAnyOfWrappers}}
+{{#discriminator}}
+import kotlinx.serialization.KSerializer
+import kotlinx.serialization.encoding.Decoder
+import kotlinx.serialization.encoding.Encoder
+{{/discriminator}}
+{{/generateOneOfAnyOfWrappers}}
+{{/enumUnknownDefaultCase}}
+{{#generateOneOfAnyOfWrappers}}
+{{#discriminator}}
+import kotlinx.serialization.SerializationException
+import kotlinx.serialization.descriptors.SerialDescriptor
+import kotlinx.serialization.descriptors.buildClassSerialDescriptor
+import kotlinx.serialization.json.JsonDecoder
+import kotlinx.serialization.json.JsonEncoder
+import kotlinx.serialization.json.JsonObject
+import kotlinx.serialization.json.JsonPrimitive
+import kotlinx.serialization.json.jsonObject
+import kotlinx.serialization.json.jsonPrimitive
+{{/discriminator}}
+{{/generateOneOfAnyOfWrappers}}
 {{#hasEnums}}
 {{/hasEnums}}
 {{/kotlinx_serialization}}
@@ -57,7 +79,9 @@ import java.io.Serializable
 import {{roomModelPackage}}.{{classname}}RoomModel
 import {{packageName}}.infrastructure.ITransformForStorage
 {{/generateRoomModels}}
+{{^kotlinx_serialization}}
 import java.io.IOException
+{{/kotlinx_serialization}}
 
 /**
  * {{{description}}}
@@ -66,12 +90,68 @@ import java.io.IOException
 {{#parcelizeModels}}
 @Parcelize
 {{/parcelizeModels}}
+{{^generateOneOfAnyOfWrappers}}
+{{^discriminator}}
 {{#multiplatform}}{{^discriminator}}@Serializable{{/discriminator}}{{/multiplatform}}{{#kotlinx_serialization}}{{#serializableModel}}@KSerializable{{/serializableModel}}{{^serializableModel}}@Serializable{{/serializableModel}}{{/kotlinx_serialization}}{{#moshi}}{{#moshiCodeGen}}@JsonClass(generateAdapter = true){{/moshiCodeGen}}{{/moshi}}{{#jackson}}{{#discriminator}}{{>typeInfoAnnotation}}{{/discriminator}}{{/jackson}}
+{{/discriminator}}
+{{/generateOneOfAnyOfWrappers}}
+{{#kotlinx_serialization}}
+{{#generateOneOfAnyOfWrappers}}
+{{#discriminator}}
+@Serializable(with = {{classname}}Serializer::class)
+{{/discriminator}}
+{{/generateOneOfAnyOfWrappers}}
+{{/kotlinx_serialization}}
 {{#isDeprecated}}
 @Deprecated(message = "This schema is deprecated.")
 {{/isDeprecated}}
 {{>additionalModelTypeAnnotations}}
+{{#kotlinx_serialization}}
+{{#nonPublicApi}}internal {{/nonPublicApi}}{{^nonPublicApi}}{{#explicitApi}}public {{/explicitApi}}{{/nonPublicApi}}sealed interface {{classname}} {
+{{#discriminator.mappedModels}}
+    @JvmInline
+    {{^nonPublicApi}}{{#explicitApi}}public {{/explicitApi}}{{/nonPublicApi}} value class {{#fnToOneOfWrapperName}}{{mappingName}}{{/fnToOneOfWrapperName}}(val value: {{modelName}}) : {{classname}}
 
+{{/discriminator.mappedModels}}
+}
+
+{{#nonPublicApi}}internal {{/nonPublicApi}}{{^nonPublicApi}}{{#explicitApi}}public {{/explicitApi}}{{/nonPublicApi}}object {{classname}}Serializer : KSerializer<{{classname}}> {
+    override val descriptor: SerialDescriptor = buildClassSerialDescriptor("{{classname}}")
+
+    override fun serialize(encoder: Encoder, value: {{classname}}) {
+        require(encoder is JsonEncoder)
+        val jsonObject = when (value) {
+{{#discriminator.mappedModels}}
+            is {{classname}}.{{#fnToOneOfWrapperName}}{{mappingName}}{{/fnToOneOfWrapperName}} -> {
+                val jsonMap = encoder.json.encodeToJsonElement({{modelName}}.serializer(), value.value).jsonObject.toMutableMap()
+                jsonMap["{{discriminator.propertyBaseName}}"] = JsonPrimitive("{{mappingName}}")
+                JsonObject(jsonMap)
+            }
+{{/discriminator.mappedModels}}
+        }
+        encoder.encodeJsonElement(jsonObject)
+    }
+
+    override fun deserialize(decoder: Decoder): {{classname}} {
+        require(decoder is JsonDecoder)
+        val element = decoder.decodeJsonElement().jsonObject
+
+        val discriminatorValue = element["{{discriminator.propertyBaseName}}"]?.jsonPrimitive?.content
+            ?: throw SerializationException("Missing {{discriminator.propertyBaseName}} field")
+
+        return when (discriminatorValue) {
+{{#discriminator.mappedModels}}
+            "{{mappingName}}" -> {
+                val decoded = decoder.json.decodeFromJsonElement({{modelName}}.serializer(), element)
+                {{classname}}.{{#fnToOneOfWrapperName}}{{mappingName}}{{/fnToOneOfWrapperName}}(decoded)
+            }
+{{/discriminator.mappedModels}}
+            else -> throw SerializationException("Unknown {{classname}} {{discriminator.propertyBaseName}}: $discriminatorValue")
+        }
+    }
+}
+{{/kotlinx_serialization}}
+{{^kotlinx_serialization}}
 {{#nonPublicApi}}internal {{/nonPublicApi}}{{^nonPublicApi}}{{#explicitApi}}public {{/explicitApi}}{{/nonPublicApi}}data class {{classname}}(var actualInstance: Any? = null) {
 
     {{^nonPublicApi}}{{#explicitApi}}public {{/explicitApi}}{{/nonPublicApi}}class CustomTypeAdapterFactory : TypeAdapterFactory {
@@ -332,4 +412,5 @@ import java.io.IOException
             }
         }
     }
-}
+}
+{{/kotlinx_serialization}}

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

@@ -43,7 +43,7 @@
 import java.util.Map;
 
 import static org.openapitools.codegen.CodegenConstants.*;
-import static org.openapitools.codegen.TestUtils.assertFileContains;
+import static org.openapitools.codegen.languages.KotlinClientCodegen.GENERATE_ONEOF_ANYOF_WRAPPERS;
 
 @SuppressWarnings("static-method")
 public class KotlinClientCodegenModelTest {
@@ -502,7 +502,7 @@ private void givenSchemaObjectPropertyNameContainsDollarSignWhenGenerateThenDoll
 //        properties.put(CodegenConstants.LIBRARY, ClientLibrary.JVM_KTOR);
         properties.put(CodegenConstants.ENUM_PROPERTY_NAMING, CodegenConstants.ENUM_PROPERTY_NAMING_TYPE.UPPERCASE.toString());
         properties.put(SERIALIZATION_LIBRARY, KotlinClientCodegen.SERIALIZATION_LIBRARY_TYPE.gson.toString());
-        properties.put(KotlinClientCodegen.GENERATE_ONEOF_ANYOF_WRAPPERS, true);
+        properties.put(GENERATE_ONEOF_ANYOF_WRAPPERS, true);
         properties.put(API_PACKAGE, "com.toasttab.service.scim.api");
         properties.put(MODEL_PACKAGE, "com.toasttab.service.scim.models");
         properties.put(PACKAGE_NAME, "com.toasttab.service.scim");
@@ -661,6 +661,7 @@ public void emptyModelKotlinxSerializationTest() throws IOException {
                 .setGeneratorName("kotlin")
                 .setAdditionalProperties(new HashMap<>() {{
                     put(CodegenConstants.MODEL_PACKAGE, "model");
+                    put(GENERATE_ONEOF_ANYOF_WRAPPERS, false);
                     put(SERIALIZATION_LIBRARY, "kotlinx_serialization");
                 }})
                 .setInputSpec("src/test/resources/3_0/kotlin/empty-model.yaml")

modules/openapi-generator/src/test/resources/3_0/kotlin/polymorphism-oneof-discriminator.yaml

@@ -0,0 +1,83 @@
+openapi: 3.0.1
+info:
+  title: Example
+  description: An example
+  version: '0.1'
+  contact:
+    email: [email protected]
+    url: 'https://example.org'
+servers:
+  - url: http://example.org
+tags:
+  - name: bird
+paths:
+  '/v1/bird/{id}':
+    get:
+      tags:
+        - bird
+      responses:
+        '200':
+          description: OK
+          content:
+            application/json:
+              schema:
+                $ref: '#/components/schemas/animal'
+      operationId: get-bird
+    parameters:
+      - schema:
+          type: string
+          format: uuid
+        name: id
+        in: path
+        required: true
+components:
+  schemas:
+    animal:
+      title: An animal
+      oneOf:
+        - $ref: '#/components/schemas/bird'
+        - $ref: '#/components/schemas/robobird'
+      discriminator:
+        propertyName: discriminator
+        mapping:
+          BIRD: '#/components/schemas/bird'
+          ROBOBIRD: '#/components/schemas/robobird'
+    another_animal:
+      title: Another animal
+      oneOf:
+        - $ref: '#/components/schemas/bird'
+        - $ref: '#/components/schemas/robobird'
+      discriminator:
+        propertyName: another_discriminator
+        mapping:
+          ANOTHER_BIRD: '#/components/schemas/bird'
+          ANOTHER_ROBOBIRD: '#/components/schemas/robobird'
+
+    bird:
+      title: A bird
+      required:
+        - discriminator
+        - another_discriminator
+      properties:
+        propertyA:
+          type: string
+        sameNameProperty:
+          type: integer
+        discriminator:
+          type: string
+        another_discriminator:
+          type: string
+    robobird:
+      title: A robo-bird
+      required:
+        - discriminator
+        - another_discriminator
+      properties:
+        propertyB:
+          type: string
+        sameNameProperty:
+          type: string
+        discriminator:
+          type: string
+        another_discriminator:
+          type: string

samples/client/others/kotlin-oneOf-discriminator-kotlinx-serialization/.openapi-generator-ignore

@@ -0,0 +1,23 @@
+# OpenAPI Generator Ignore
+# Generated by openapi-generator https://github.com/openapitools/openapi-generator
+
+# Use this file to prevent files from being overwritten by the generator.
+# The patterns follow closely to .gitignore or .dockerignore.
+
+# As an example, the C# client generator defines ApiClient.cs.
+# You can make changes and tell OpenAPI Generator to ignore just this file by uncommenting the following line:
+#ApiClient.cs
+
+# You can match any string of characters against a directory, file or extension with a single asterisk (*):
+#foo/*/qux
+# The above matches foo/bar/qux and foo/baz/qux, but not foo/bar/baz/qux
+
+# You can recursively match patterns against a directory, file or extension with a double asterisk (**):
+#foo/**/qux
+# This matches foo/bar/qux, foo/baz/qux, and foo/bar/baz/qux
+
+# You can also negate patterns with an exclamation (!).
+# For example, you can ignore all files in a docs folder with the file extension .md:
+#docs/*.md
+# Then explicitly reverse the ignore rule for a single file:
+#!docs/README.md