[BUG][KOTLIN] Sanitize names of the adapter variables in anyOf and oneOf model template to avoid compilation errors (#19981)

* [kotlin] Sanitize one_of and any_of model variable names to avoid compilation errors (#19942)

* [kotlin] add missing validateJsonElement method to oneOf and anyOf model templates (#19942)

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

@@ -83,7 +83,7 @@ import java.io.IOException
             {{#anyOf}}
             {{^isArray}}
             {{^vendorExtensions.x-duplicated-data-type}}
-            val adapter{{{dataType}}} = gson.getDelegateAdapter(this, TypeToken.get({{{dataType}}}::class.java))
+            val adapter{{#sanitizeGeneric}}{{{dataType}}}{{/sanitizeGeneric}} = gson.getDelegateAdapter(this, TypeToken.get({{{dataType}}}::class.java))
             {{/vendorExtensions.x-duplicated-data-type}}
             {{/isArray}}
             {{#isArray}}
@@ -122,7 +122,7 @@ import java.io.IOException
                         return
                     {{/isPrimitiveType}}
                     {{^isPrimitiveType}}
-                        val element = adapter{{{dataType}}}.toJsonTree(value.actualInstance as {{{dataType}}}?)
+                        val element = adapter{{#sanitizeGeneric}}{{{dataType}}}{{/sanitizeGeneric}}.toJsonTree(value.actualInstance as {{{dataType}}}?)
                         elementAdapter.write(out, element)
                         return
                     {{/isPrimitiveType}}
@@ -185,7 +185,7 @@ import java.io.IOException
                         for(element in jsonElement.getAsJsonArray()) {
                         {{#items}}
                         {{#isNumber}}
-                            require(jsonElement.getAsJsonPrimitive().isNumber) {
+                            require(element.getAsJsonPrimitive().isNumber) {
                                 String.format("Expected json element to be of type Number in the JSON string but got `%s`", jsonElement.toString())
                             }
                         {{/isNumber}}
@@ -238,4 +238,99 @@ import java.io.IOException
             }.nullSafe() as TypeAdapter<T>
         }
     }
+
+    companion object {
+        /**
+        * Validates the JSON Element and throws an exception if issues found
+        *
+        * @param jsonElement JSON Element
+        * @throws IOException if the JSON Element is invalid with respect to {{classname}}
+        */
+        @Throws(IOException::class)
+        fun validateJsonElement(jsonElement: JsonElement?) {
+            requireNotNull(jsonElement) {
+                "Provided json element must not be null"
+            }
+            var match = 0
+            val errorMessages = ArrayList<String>()
+            {{#composedSchemas}}
+            {{#anyOf}}
+            {{^vendorExtensions.x-duplicated-data-type}}
+            {{^hasVars}}
+            // validate the json string with {{{dataType}}}
+            try {
+                // validate the JSON object to see if any exception is thrown
+            {{^isArray}}
+            {{#isNumber}}
+                require(jsonElement.getAsJsonPrimitive().isNumber()) {
+                    String.format("Expected json element to be of type Number in the JSON string but got `%s`", jsonElement.toString())
+                }
+            {{/isNumber}}
+            {{^isNumber}}
+            {{#isPrimitiveType}}
+                require(jsonElement.getAsJsonPrimitive().is{{#isBoolean}}Boolean{{/isBoolean}}{{#isString}}String{{/isString}}{{^isString}}{{^isBoolean}}Number{{/isBoolean}}{{/isString}}()) {
+                    String.format("Expected json element to be of type {{#isBoolean}}Boolean{{/isBoolean}}{{#isString}}String{{/isString}}{{^isString}}{{^isBoolean}}Number{{/isBoolean}}{{/isString}} in the JSON string but got `%s`", jsonElement.toString())
+                }
+            {{/isPrimitiveType}}
+            {{/isNumber}}
+            {{^isNumber}}
+            {{^isPrimitiveType}}
+                {{{dataType}}}.validateJsonElement(jsonElement)
+            {{/isPrimitiveType}}
+            {{/isNumber}}
+            {{/isArray}}
+            {{#isArray}}
+                require(jsonElement.isJsonArray) {
+                    String.format("Expected json element to be a array type in the JSON string but got `%s`", jsonElement.toString())
+                }
+
+                // validate array items
+                for(element in jsonElement.getAsJsonArray()) {
+                {{#items}}
+                {{#isNumber}}
+                    require(element.getAsJsonPrimitive().isNumber) {
+                        String.format("Expected json element to be of type Number in the JSON string but got `%s`", jsonElement.toString())
+                    }
+                {{/isNumber}}
+                {{^isNumber}}
+                {{#isPrimitiveType}}
+                    require(element.getAsJsonPrimitive().is{{#isBoolean}}Boolean{{/isBoolean}}{{#isString}}String{{/isString}}{{^isString}}{{^isBoolean}}Number{{/isBoolean}}{{/isString}}) {
+                        String.format("Expected array items to be of type {{#isBoolean}}Boolean{{/isBoolean}}{{#isString}}String{{/isString}}{{^isString}}{{^isBoolean}}Number{{/isBoolean}}{{/isString}} in the JSON string but got `%s`", jsonElement.toString())
+                    }
+                {{/isPrimitiveType}}
+                {{/isNumber}}
+                {{^isNumber}}
+                {{^isPrimitiveType}}
+                    {{{dataType}}}.validateJsonElement(element)
+                {{/isPrimitiveType}}
+                {{/isNumber}}
+                {{/items}}
+                }
+            {{/isArray}}
+                match++
+            } catch (e: Exception) {
+                // Validation failed, continue
+                errorMessages.add(String.format("Validation for {{{dataType}}} failed with `%s`.", e.message))
+            }
+            {{/hasVars}}
+            {{#hasVars}}
+            // validate json string for {{{.}}}
+            try {
+                // validate the JSON object to see if any exception is thrown
+                {{.}}.validateJsonElement(jsonElement)
+                match++
+            } catch (e: Exception) {
+                // validation failed, continue
+                errorMessages.add(String.format("Validation for {{{.}}} failed with `%s`.", e.message))
+            }
+            {{/hasVars}}
+            {{/vendorExtensions.x-duplicated-data-type}}
+            {{/anyOf}}
+            {{/composedSchemas}}
+
+            if (match != 1) {
+                throw IOException(String.format("Failed validation for {{classname}}: %d classes match result, expected 1. Detailed failure message for oneOf schemas: %s. JSON: %s", match, errorMessages, jsonElement.toString()))
+            }
+        }
+    }
 }

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

@@ -83,7 +83,7 @@ import java.io.IOException
             {{#oneOf}}
             {{^isArray}}
             {{^vendorExtensions.x-duplicated-data-type}}
-            val adapter{{{dataType}}} = gson.getDelegateAdapter(this, TypeToken.get({{{dataType}}}::class.java))
+            val adapter{{#sanitizeGeneric}}{{{dataType}}}{{/sanitizeGeneric}} = gson.getDelegateAdapter(this, TypeToken.get({{{dataType}}}::class.java))
             {{/vendorExtensions.x-duplicated-data-type}}
             {{/isArray}}
             {{#isArray}}
@@ -122,7 +122,7 @@ import java.io.IOException
                         return
                     {{/isPrimitiveType}}
                     {{^isPrimitiveType}}
-                        val element = adapter{{{dataType}}}.toJsonTree(value.actualInstance as {{{dataType}}}?)
+                        val element = adapter{{#sanitizeGeneric}}{{{dataType}}}{{/sanitizeGeneric}}.toJsonTree(value.actualInstance as {{{dataType}}}?)
                         elementAdapter.write(out, element)
                         return
                     {{/isPrimitiveType}}
@@ -179,7 +179,7 @@ import java.io.IOException
                         for(element in jsonElement.getAsJsonArray()) {
                         {{#items}}
                         {{#isNumber}}
-                            require(jsonElement.getAsJsonPrimitive().isNumber) {
+                            require(element.getAsJsonPrimitive().isNumber) {
                                 String.format("Expected json element to be of type Number in the JSON string but got `%s`", jsonElement.toString())
                             }
                         {{/isNumber}}
@@ -236,4 +236,99 @@ import java.io.IOException
             }.nullSafe() as TypeAdapter<T>
         }
     }
+
+    companion object {
+        /**
+        * Validates the JSON Element and throws an exception if issues found
+        *
+        * @param jsonElement JSON Element
+        * @throws IOException if the JSON Element is invalid with respect to {{classname}}
+        */
+        @Throws(IOException::class)
+        fun validateJsonElement(jsonElement: JsonElement?) {
+            requireNotNull(jsonElement) {
+                "Provided json element must not be null"
+            }
+            var match = 0
+            val errorMessages = ArrayList<String>()
+            {{#composedSchemas}}
+            {{#oneOf}}
+            {{^vendorExtensions.x-duplicated-data-type}}
+            {{^hasVars}}
+            // validate the json string with {{{dataType}}}
+            try {
+                // validate the JSON object to see if any exception is thrown
+            {{^isArray}}
+            {{#isNumber}}
+                require(jsonElement.getAsJsonPrimitive().isNumber()) {
+                    String.format("Expected json element to be of type Number in the JSON string but got `%s`", jsonElement.toString())
+                }
+            {{/isNumber}}
+            {{^isNumber}}
+            {{#isPrimitiveType}}
+                require(jsonElement.getAsJsonPrimitive().is{{#isBoolean}}Boolean{{/isBoolean}}{{#isString}}String{{/isString}}{{^isString}}{{^isBoolean}}Number{{/isBoolean}}{{/isString}}()) {
+                    String.format("Expected json element to be of type {{#isBoolean}}Boolean{{/isBoolean}}{{#isString}}String{{/isString}}{{^isString}}{{^isBoolean}}Number{{/isBoolean}}{{/isString}} in the JSON string but got `%s`", jsonElement.toString())
+                }
+            {{/isPrimitiveType}}
+            {{/isNumber}}
+            {{^isNumber}}
+            {{^isPrimitiveType}}
+                {{{dataType}}}.validateJsonElement(jsonElement)
+            {{/isPrimitiveType}}
+            {{/isNumber}}
+            {{/isArray}}
+            {{#isArray}}
+                require(jsonElement.isJsonArray) {
+                    String.format("Expected json element to be a array type in the JSON string but got `%s`", jsonElement.toString())
+                }
+
+                // validate array items
+                for(element in jsonElement.getAsJsonArray()) {
+                {{#items}}
+                {{#isNumber}}
+                    require(jsonElement.getAsJsonPrimitive().isNumber) {
+                        String.format("Expected json element to be of type Number in the JSON string but got `%s`", jsonElement.toString())
+                    }
+                {{/isNumber}}
+                {{^isNumber}}
+                {{#isPrimitiveType}}
+                    require(element.getAsJsonPrimitive().is{{#isBoolean}}Boolean{{/isBoolean}}{{#isString}}String{{/isString}}{{^isString}}{{^isBoolean}}Number{{/isBoolean}}{{/isString}}) {
+                        String.format("Expected array items to be of type {{#isBoolean}}Boolean{{/isBoolean}}{{#isString}}String{{/isString}}{{^isString}}{{^isBoolean}}Number{{/isBoolean}}{{/isString}} in the JSON string but got `%s`", jsonElement.toString())
+                    }
+                {{/isPrimitiveType}}
+                {{/isNumber}}
+                {{^isNumber}}
+                {{^isPrimitiveType}}
+                    {{{dataType}}}.validateJsonElement(element)
+                {{/isPrimitiveType}}
+                {{/isNumber}}
+                {{/items}}
+                }
+            {{/isArray}}
+                match++
+            } catch (e: Exception) {
+                // Validation failed, continue
+                errorMessages.add(String.format("Validation for {{{dataType}}} failed with `%s`.", e.message))
+            }
+            {{/hasVars}}
+            {{#hasVars}}
+            // validate json string for {{{.}}}
+            try {
+                // validate the JSON object to see if any exception is thrown
+                {{.}}.validateJsonElement(jsonElement)
+                match++
+            } catch (e: Exception) {
+                // validation failed, continue
+                errorMessages.add(String.format("Validation for {{{.}}} failed with `%s`.", e.message))
+            }
+            {{/hasVars}}
+            {{/vendorExtensions.x-duplicated-data-type}}
+            {{/oneOf}}
+            {{/composedSchemas}}
+
+            if (match != 1) {
+                throw IOException(String.format("Failed validation for {{classname}}: %d classes match result, expected 1. Detailed failure message for oneOf schemas: %s. JSON: %s", match, errorMessages, jsonElement.toString()))
+            }
+        }
+    }
 }

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

@@ -0,0 +1,29 @@
+package org.openapitools.codegen.kotlin;
+
+import lombok.Getter;
+import org.jetbrains.kotlin.com.intellij.openapi.util.text.Strings;
+
+@Getter
+enum ClientLibrary {
+    JVM_KTOR("main/kotlin"),
+    JVM_OKHTTP4("main/kotlin"),
+    JVM_SPRING_WEBCLIENT("main/kotlin"),
+    JVM_SPRING_RESTCLIENT("main/kotlin"),
+    JVM_RETROFIT2("main/kotlin"),
+    MULTIPLATFORM("commonMain/kotlin"),
+    JVM_VOLLEY("gson", "main/java"),
+    JVM_VERTX("main/kotlin");
+    private final String serializationLibrary;
+    private final String libraryName;
+    private final String sourceRoot;
+
+    ClientLibrary(String serializationLibrary, String sourceRoot) {
+        this.serializationLibrary = serializationLibrary;
+        this.sourceRoot = sourceRoot;
+        this.libraryName = Strings.toLowerCase(this.name()).replace("_", "-");
+    }
+
+    ClientLibrary(String sourceRoot) {
+        this("jackson", sourceRoot);
+    }
+}

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

@@ -22,7 +22,7 @@ import static org.openapitools.codegen.TestUtils.assertFileContains;
 
 public class KotlinClientCodegenApiTest {
 
-    @DataProvider(name = "pathResponses")
+    @DataProvider(name = "clientLibraries")
     public Object[][] pathResponses() {
         return new Object[][]{
                 {ClientLibrary.JVM_KTOR},
@@ -36,7 +36,7 @@ public class KotlinClientCodegenApiTest {
         };
     }
 
-    @Test(dataProvider = "pathResponses")
+    @Test(dataProvider = "clientLibraries")
     void testPathVariableIsNotEscaped_19930(ClientLibrary library) throws IOException {
 
         OpenAPI openAPI = new OpenAPIParser()
@@ -76,29 +76,4 @@ public class KotlinClientCodegenApiTest {
         codegen.additionalProperties().put(KotlinClientCodegen.DATE_LIBRARY, "kotlinx-datetime");
         return codegen;
     }
-
-    @Getter
-    private enum ClientLibrary {
-        JVM_KTOR("main/kotlin"),
-        JVM_OKHTTP4("main/kotlin"),
-        JVM_SPRING_WEBCLIENT("main/kotlin"),
-        JVM_SPRING_RESTCLIENT("main/kotlin"),
-        JVM_RETROFIT2("main/kotlin"),
-        MULTIPLATFORM("commonMain/kotlin"),
-        JVM_VOLLEY("gson", "main/java"),
-        JVM_VERTX("main/kotlin");
-        private final String serializationLibrary;
-        private final String libraryName;
-        private final String sourceRoot;
-
-        ClientLibrary(String serializationLibrary, String sourceRoot) {
-            this.serializationLibrary = serializationLibrary;
-            this.sourceRoot = sourceRoot;
-            this.libraryName = Strings.toLowerCase(this.name()).replace("_", "-");
-        }
-
-        ClientLibrary(String sourceRoot) {
-            this("jackson", sourceRoot);
-        }
-    }
 }

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

@@ -433,6 +433,66 @@ public class KotlinClientCodegenModelTest {
         configAssert.assertValue(KotlinClientCodegen.FAIL_ON_UNKNOWN_PROPERTIES, codegen::isFailOnUnknownProperties, Boolean.FALSE);
     }
 
+    @DataProvider(name = "gsonClientLibraries")
+    public Object[][] pathResponses() {
+        return new Object[][]{
+                {ClientLibrary.JVM_KTOR},
+                {ClientLibrary.JVM_OKHTTP4},
+                {ClientLibrary.JVM_RETROFIT2},
+                {ClientLibrary.MULTIPLATFORM},
+                {ClientLibrary.JVM_VOLLEY},
+                {ClientLibrary.JVM_VERTX}
+        };
+    }
+
+    @Test(dataProvider = "gsonClientLibraries")
+    public void testLocalVariablesUseSanitizedDataTypeNamesForOneOfProperty_19942(ClientLibrary clientLibrary) throws IOException {
+        File output = Files.createTempDirectory("test").toFile();
+        String path = output.getAbsolutePath();
+        output.deleteOnExit();
+
+        final CodegenConfigurator configurator = new CodegenConfigurator()
+                .setGeneratorName("kotlin")
+                .setLibrary(clientLibrary.getLibraryName())
+                .setInputSpec("src/test/resources/3_0/issue_19942.json")
+                .addAdditionalProperty("omitGradleWrapper", true)
+                .addAdditionalProperty("serializationLibrary", "gson")
+                .addAdditionalProperty("dateLibrary", "kotlinx-datetime")
+                .addAdditionalProperty("useSpringBoot3", "true")
+                .addAdditionalProperty("generateOneOfAnyOfWrappers", true)
+                .setOutputDir(output.getAbsolutePath().replace("\\", "/"));
+        DefaultGenerator generator = new DefaultGenerator();
+
+        generator.opts(configurator.toClientOptInput()).generate();
+
+        TestUtils.assertFileNotContains(Paths.get(path + "/src/" + clientLibrary.getSourceRoot() + "/org/openapitools/client/models/ObjectWithComplexOneOfId.kt"),
+                "val adapterkotlin.String", "val adapterjava.math.BigDecimal");
+    }
+
+    @Test(dataProvider = "gsonClientLibraries")
+    public void testLocalVariablesUseSanitizedDataTypeNamesForAnyOfProperty_19942(ClientLibrary clientLibrary) throws IOException {
+        File output = Files.createTempDirectory("test").toFile();
+        String path = output.getAbsolutePath();
+        output.deleteOnExit();
+
+        final CodegenConfigurator configurator = new CodegenConfigurator()
+                .setGeneratorName("kotlin")
+                .setLibrary(clientLibrary.getLibraryName())
+                .setInputSpec("src/test/resources/3_0/issue_19942.json")
+                .addAdditionalProperty("omitGradleWrapper", true)
+                .addAdditionalProperty("serializationLibrary", "gson")
+                .addAdditionalProperty("dateLibrary", "kotlinx-datetime")
+                .addAdditionalProperty("useSpringBoot3", "true")
+                .addAdditionalProperty("generateOneOfAnyOfWrappers", true)
+                .setOutputDir(output.getAbsolutePath().replace("\\", "/"));
+        DefaultGenerator generator = new DefaultGenerator();
+
+        generator.opts(configurator.toClientOptInput()).generate();
+
+        TestUtils.assertFileNotContains(Paths.get(path + "/src/" + clientLibrary.getSourceRoot() + "/org/openapitools/client/models/ObjectWithComplexAnyOfId.kt"),
+                "val adapterkotlin.String", "val adapterjava.math.BigDecimal");
+    }
+
     private static class ModelNameTest {
         private final String expectedName;
         private final String expectedClassName;

modules/openapi-generator/src/test/resources/3_0/issue_19942.json

@@ -0,0 +1,72 @@
+{
+  "openapi": "3.0.1",
+  "info": {
+    "title": "xxxxx",
+    "version": "1.0"
+  },
+  "servers": [
+    {
+      "url": "https://xxxxx"
+    },
+    {
+      "url": "http://localhost:3000"
+    }
+  ],
+  "paths": {
+    "/test": {
+      "get": {
+        "operationId": "testOneOf",
+        "tags": [
+          "testOneOf"
+        ],
+        "summary": "fetches oneOf id",
+        "responses": {
+          "200": {
+            "description": "ok",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/ObjectWithComplexOneOf"
+                }
+              }
+            }
+          }
+        }
+      }
+    }
+  },
+  "components" : {
+    "schemas": {
+      "ObjectWithComplexOneOf" : {
+        "type": "object",
+        "properties": {
+          "id": {
+            "oneOf": [
+              {
+                "type": "string"
+              },
+              {
+                "type": "number"
+              }
+            ]
+          }
+        }
+      },
+      "ObjectWithComplexAnyOf" : {
+        "type": "object",
+        "properties": {
+          "id": {
+            "anyOf": [
+              {
+                "type": "string"
+              },
+              {
+                "type": "number"
+              }
+            ]
+          }
+        }
+      }
+    }
+  }
+}

samples/client/petstore/kotlin-model-prefix-type-mappings/src/main/kotlin/org/openapitools/client/models/ApiAnyOfUserOrPet.kt

@@ -111,4 +111,43 @@ data class ApiAnyOfUserOrPet(var actualInstance: Any? = null) {
             }.nullSafe() as TypeAdapter<T>
         }
     }
+
+    companion object {
+        /**
+        * Validates the JSON Element and throws an exception if issues found
+        *
+        * @param jsonElement JSON Element
+        * @throws IOException if the JSON Element is invalid with respect to ApiAnyOfUserOrPet
+        */
+        @Throws(IOException::class)
+        fun validateJsonElement(jsonElement: JsonElement?) {
+            requireNotNull(jsonElement) {
+                "Provided json element must not be null"
+            }
+            var match = 0
+            val errorMessages = ArrayList<String>()
+            // validate the json string with ApiUser
+            try {
+                // validate the JSON object to see if any exception is thrown
+                ApiUser.validateJsonElement(jsonElement)
+                match++
+            } catch (e: Exception) {
+                // Validation failed, continue
+                errorMessages.add(String.format("Validation for ApiUser failed with `%s`.", e.message))
+            }
+            // validate the json string with ApiPet
+            try {
+                // validate the JSON object to see if any exception is thrown
+                ApiPet.validateJsonElement(jsonElement)
+                match++
+            } catch (e: Exception) {
+                // Validation failed, continue
+                errorMessages.add(String.format("Validation for ApiPet failed with `%s`.", e.message))
+            }
+
+            if (match != 1) {
+                throw IOException(String.format("Failed validation for ApiAnyOfUserOrPet: %d classes match result, expected 1. Detailed failure message for oneOf schemas: %s. JSON: %s", match, errorMessages, jsonElement.toString()))
+            }
+        }
+    }
 }

samples/client/petstore/kotlin-model-prefix-type-mappings/src/main/kotlin/org/openapitools/client/models/ApiAnyOfUserOrPetOrArrayString.kt

@@ -144,4 +144,61 @@ data class ApiAnyOfUserOrPetOrArrayString(var actualInstance: Any? = null) {
             }.nullSafe() as TypeAdapter<T>
         }
     }
+
+    companion object {
+        /**
+        * Validates the JSON Element and throws an exception if issues found
+        *
+        * @param jsonElement JSON Element
+        * @throws IOException if the JSON Element is invalid with respect to ApiAnyOfUserOrPetOrArrayString
+        */
+        @Throws(IOException::class)
+        fun validateJsonElement(jsonElement: JsonElement?) {
+            requireNotNull(jsonElement) {
+                "Provided json element must not be null"
+            }
+            var match = 0
+            val errorMessages = ArrayList<String>()
+            // validate the json string with ApiUser
+            try {
+                // validate the JSON object to see if any exception is thrown
+                ApiUser.validateJsonElement(jsonElement)
+                match++
+            } catch (e: Exception) {
+                // Validation failed, continue
+                errorMessages.add(String.format("Validation for ApiUser failed with `%s`.", e.message))
+            }
+            // validate the json string with ApiPet
+            try {
+                // validate the JSON object to see if any exception is thrown
+                ApiPet.validateJsonElement(jsonElement)
+                match++
+            } catch (e: Exception) {
+                // Validation failed, continue
+                errorMessages.add(String.format("Validation for ApiPet failed with `%s`.", e.message))
+            }
+            // validate the json string with kotlin.collections.List<kotlin.String>
+            try {
+                // validate the JSON object to see if any exception is thrown
+                require(jsonElement.isJsonArray) {
+                    String.format("Expected json element to be a array type in the JSON string but got `%s`", jsonElement.toString())
+                }
+
+                // validate array items
+                for(element in jsonElement.getAsJsonArray()) {
+                    require(element.getAsJsonPrimitive().isString) {
+                        String.format("Expected array items to be of type String in the JSON string but got `%s`", jsonElement.toString())
+                    }
+                }
+                match++
+            } catch (e: Exception) {
+                // Validation failed, continue
+                errorMessages.add(String.format("Validation for kotlin.collections.List<kotlin.String> failed with `%s`.", e.message))
+            }
+
+            if (match != 1) {
+                throw IOException(String.format("Failed validation for ApiAnyOfUserOrPetOrArrayString: %d classes match result, expected 1. Detailed failure message for oneOf schemas: %s. JSON: %s", match, errorMessages, jsonElement.toString()))
+            }
+        }
+    }
 }

samples/client/petstore/kotlin-model-prefix-type-mappings/src/main/kotlin/org/openapitools/client/models/ApiUserOrPet.kt

@@ -115,4 +115,43 @@ data class ApiUserOrPet(var actualInstance: Any? = null) {
             }.nullSafe() as TypeAdapter<T>
         }
     }
+
+    companion object {
+        /**
+        * Validates the JSON Element and throws an exception if issues found
+        *
+        * @param jsonElement JSON Element
+        * @throws IOException if the JSON Element is invalid with respect to ApiUserOrPet
+        */
+        @Throws(IOException::class)
+        fun validateJsonElement(jsonElement: JsonElement?) {
+            requireNotNull(jsonElement) {
+                "Provided json element must not be null"
+            }
+            var match = 0
+            val errorMessages = ArrayList<String>()
+            // validate the json string with ApiUser
+            try {
+                // validate the JSON object to see if any exception is thrown
+                ApiUser.validateJsonElement(jsonElement)
+                match++
+            } catch (e: Exception) {
+                // Validation failed, continue
+                errorMessages.add(String.format("Validation for ApiUser failed with `%s`.", e.message))
+            }
+            // validate the json string with ApiPet
+            try {
+                // validate the JSON object to see if any exception is thrown
+                ApiPet.validateJsonElement(jsonElement)
+                match++
+            } catch (e: Exception) {
+                // Validation failed, continue
+                errorMessages.add(String.format("Validation for ApiPet failed with `%s`.", e.message))
+            }
+
+            if (match != 1) {
+                throw IOException(String.format("Failed validation for ApiUserOrPet: %d classes match result, expected 1. Detailed failure message for oneOf schemas: %s. JSON: %s", match, errorMessages, jsonElement.toString()))
+            }
+        }
+    }
 }

samples/client/petstore/kotlin-model-prefix-type-mappings/src/main/kotlin/org/openapitools/client/models/ApiUserOrPetOrArrayString.kt

@@ -147,4 +147,61 @@ data class ApiUserOrPetOrArrayString(var actualInstance: Any? = null) {
             }.nullSafe() as TypeAdapter<T>
         }
     }
+
+    companion object {
+        /**
+        * Validates the JSON Element and throws an exception if issues found
+        *
+        * @param jsonElement JSON Element
+        * @throws IOException if the JSON Element is invalid with respect to ApiUserOrPetOrArrayString
+        */
+        @Throws(IOException::class)
+        fun validateJsonElement(jsonElement: JsonElement?) {
+            requireNotNull(jsonElement) {
+                "Provided json element must not be null"
+            }
+            var match = 0
+            val errorMessages = ArrayList<String>()
+            // validate the json string with ApiUser
+            try {
+                // validate the JSON object to see if any exception is thrown
+                ApiUser.validateJsonElement(jsonElement)
+                match++
+            } catch (e: Exception) {
+                // Validation failed, continue
+                errorMessages.add(String.format("Validation for ApiUser failed with `%s`.", e.message))
+            }
+            // validate the json string with ApiPet
+            try {
+                // validate the JSON object to see if any exception is thrown
+                ApiPet.validateJsonElement(jsonElement)
+                match++
+            } catch (e: Exception) {
+                // Validation failed, continue
+                errorMessages.add(String.format("Validation for ApiPet failed with `%s`.", e.message))
+            }
+            // validate the json string with kotlin.collections.List<kotlin.String>
+            try {
+                // validate the JSON object to see if any exception is thrown
+                require(jsonElement.isJsonArray) {
+                    String.format("Expected json element to be a array type in the JSON string but got `%s`", jsonElement.toString())
+                }
+
+                // validate array items
+                for(element in jsonElement.getAsJsonArray()) {
+                    require(element.getAsJsonPrimitive().isString) {
+                        String.format("Expected array items to be of type String in the JSON string but got `%s`", jsonElement.toString())
+                    }
+                }
+                match++
+            } catch (e: Exception) {
+                // Validation failed, continue
+                errorMessages.add(String.format("Validation for kotlin.collections.List<kotlin.String> failed with `%s`.", e.message))
+            }
+
+            if (match != 1) {
+                throw IOException(String.format("Failed validation for ApiUserOrPetOrArrayString: %d classes match result, expected 1. Detailed failure message for oneOf schemas: %s. JSON: %s", match, errorMessages, jsonElement.toString()))
+            }
+        }
+    }
 }