Add tests for kotlin interop

buildSrc/build.gradle.kts

@@ -14,6 +14,7 @@ repositories {
 
 dependencies {
     implementation(plugin(libs.plugins.errorprone))
+    implementation(plugin(libs.plugins.kotlin.jvm))
 }
 
 fun plugin(plugin: Provider<PluginDependency>): Provider<String> = plugin.map {

buildSrc/src/main/kotlin/internal.kotlin-interop-convention.gradle.kts

@@ -0,0 +1,9 @@
+plugins {
+    id("org.jetbrains.kotlin.jvm")
+}
+
+kotlin {
+    compilerOptions {
+        javaParameters = true
+    }
+}

gradle/libs.versions.toml

@@ -2,6 +2,7 @@
 jspecify = "1.0.0"
 errorprone = "2.48.0"
 errorprone-plugin = "5.1.0"
+kotlin = "2.3.10"
 nmcp = "1.4.4"
 nullaway = "0.13.1"
 problem4j-core = "1.4.3"
@@ -12,6 +13,7 @@ spring-boot = "4.0.3"
 
 [plugins]
 errorprone = { id = "net.ltgt.errorprone", version.ref = "errorprone-plugin" }
+kotlin-jvm = { id = "org.jetbrains.kotlin.jvm", version.ref = "kotlin" }
 nmcp = { id = "com.gradleup.nmcp", version.ref = "nmcp" }
 nmcp-aggregation = { id = "com.gradleup.nmcp.aggregation", version.ref = "nmcp" }
 spotless = { id = "com.diffplug.spotless", version.ref = "spotless" }
@@ -23,6 +25,7 @@ spring-boot-dependencies = { module = "org.springframework.boot:spring-boot-depe
 # direct versions
 errorprone-core = { module = "com.google.errorprone:error_prone_core", version.ref = "errorprone" }
 jspecify = { module = "org.jspecify:jspecify", version.ref = "jspecify" }
+kotlin-reflect = { module = "org.jetbrains.kotlin:kotlin-reflect", version.ref = "kotlin" }
 nullaway = { module = "com.uber.nullaway:nullaway", version.ref = "nullaway" }
 problem4j-core = { module = "io.github.problem4j:problem4j-core", version.ref = "problem4j-core" }
 problem4j-jackson2 = { module = "io.github.problem4j:problem4j-jackson2", version.ref = "problem4j-jackson2" }
@@ -45,6 +48,7 @@ spring-boot-starter-webmvc-test = { module = "org.springframework.boot:spring-bo
 spring-web = { module = "org.springframework:spring-web" }
 jackson2-databind = { module = "com.fasterxml.jackson.core:jackson-databind" }
 jackson3-dataformat-xml = { module = "tools.jackson.dataformat:jackson-dataformat-xml" }
+jackson3-module-kotlin = { module = "tools.jackson.module:jackson-module-kotlin" }
 jakarta-servlet-api = { module = "jakarta.servlet:jakarta.servlet-api" }
 jakarta-validation-api = { module = "jakarta.validation:jakarta.validation-api" }
 junit-platform-launcher = { module = "org.junit.platform:junit-platform-launcher" }

problem4j-spring-webflux/build.gradle.kts

@@ -2,6 +2,7 @@ plugins {
     id("internal.errorprone-convention")
     id("internal.jacoco-convention")
     id("internal.java-library-convention")
+    id("internal.kotlin-interop-convention")
     id("internal.publishing-convention")
     alias(libs.plugins.nmcp)
 }
@@ -25,6 +26,8 @@ dependencies {
     testImplementation(libs.spring.boot.starter.webflux)
     testImplementation(libs.spring.boot.starter.webflux.test)
     testImplementation(libs.spring.boot.validation)
+    testImplementation(libs.jackson3.module.kotlin)
+    testImplementation(libs.kotlin.reflect)
 
     testRuntimeOnly(libs.junit.platform.launcher)
 

problem4j-spring-webflux/src/test/java/io/github/problem4j/spring/webflux/app/rest/BindingKotlinController.java

@@ -0,0 +1,140 @@
+/*
+ * Copyright (c) 2025-2026 The Problem4J Authors
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+package io.github.problem4j.spring.webflux.app.rest;
+
+import io.github.problem4j.spring.webflux.app.model.KotlinModel;
+import org.springframework.http.MediaType;
+import org.springframework.web.bind.annotation.PostMapping;
+import org.springframework.web.bind.annotation.RequestBody;
+import org.springframework.web.bind.annotation.RequestMapping;
+import org.springframework.web.bind.annotation.RestController;
+
+@RestController
+@RequestMapping("/binding-kotlin")
+public class BindingKotlinController {
+
+  @PostMapping(path = "/int", consumes = MediaType.APPLICATION_JSON_VALUE)
+  public String intValue(@RequestBody KotlinModel.KotlinIntRequest request) {
+    return "OK";
+  }
+
+  @PostMapping(path = "/long", consumes = MediaType.APPLICATION_JSON_VALUE)
+  public String longValue(@RequestBody KotlinModel.KotlinLongRequest request) {
+    return "OK";
+  }
+
+  @PostMapping(path = "/short", consumes = MediaType.APPLICATION_JSON_VALUE)
+  public String shortValue(@RequestBody KotlinModel.KotlinShortRequest request) {
+    return "OK";
+  }
+
+  @PostMapping(path = "/byte", consumes = MediaType.APPLICATION_JSON_VALUE)
+  public String byteValue(@RequestBody KotlinModel.KotlinByteRequest request) {
+    return "OK";
+  }
+
+  @PostMapping(path = "/float", consumes = MediaType.APPLICATION_JSON_VALUE)
+  public String floatValue(@RequestBody KotlinModel.KotlinFloatRequest request) {
+    return "OK";
+  }
+
+  @PostMapping(path = "/double", consumes = MediaType.APPLICATION_JSON_VALUE)
+  public String doubleValue(@RequestBody KotlinModel.KotlinDoubleRequest request) {
+    return "OK";
+  }
+
+  @PostMapping(path = "/boolean", consumes = MediaType.APPLICATION_JSON_VALUE)
+  public String booleanValue(@RequestBody KotlinModel.KotlinBooleanRequest request) {
+    return "OK";
+  }
+
+  @PostMapping(path = "/nested/int", consumes = MediaType.APPLICATION_JSON_VALUE)
+  public String nestedInt(@RequestBody KotlinModel.KotlinNestedIntRequest request) {
+    return "OK";
+  }
+
+  @PostMapping(path = "/nested/long", consumes = MediaType.APPLICATION_JSON_VALUE)
+  public String nestedLong(@RequestBody KotlinModel.KotlinNestedLongRequest request) {
+    return "OK";
+  }
+
+  @PostMapping(path = "/nested/short", consumes = MediaType.APPLICATION_JSON_VALUE)
+  public String nestedShort(@RequestBody KotlinModel.KotlinNestedShortRequest request) {
+    return "OK";
+  }
+
+  @PostMapping(path = "/nested/byte", consumes = MediaType.APPLICATION_JSON_VALUE)
+  public String nestedByte(@RequestBody KotlinModel.KotlinNestedByteRequest request) {
+    return "OK";
+  }
+
+  @PostMapping(path = "/nested/float", consumes = MediaType.APPLICATION_JSON_VALUE)
+  public String nestedFloat(@RequestBody KotlinModel.KotlinNestedFloatRequest request) {
+    return "OK";
+  }
+
+  @PostMapping(path = "/nested/double", consumes = MediaType.APPLICATION_JSON_VALUE)
+  public String nestedDouble(@RequestBody KotlinModel.KotlinNestedDoubleRequest request) {
+    return "OK";
+  }
+
+  @PostMapping(path = "/nested/boolean", consumes = MediaType.APPLICATION_JSON_VALUE)
+  public String nestedBoolean(@RequestBody KotlinModel.KotlinNestedBooleanRequest request) {
+    return "OK";
+  }
+
+  @PostMapping(path = "/complex", consumes = MediaType.APPLICATION_JSON_VALUE)
+  public String complex(@RequestBody KotlinModel.KotlinComplexRequest request) {
+    return "OK";
+  }
+
+  @PostMapping(path = "/nullable", consumes = MediaType.APPLICATION_JSON_VALUE)
+  public String nullable(@RequestBody KotlinModel.KotlinNullableRequest request) {
+    return "OK";
+  }
+
+  @PostMapping(path = "/default", consumes = MediaType.APPLICATION_JSON_VALUE)
+  public String defaultValue(@RequestBody KotlinModel.KotlinDefaultRequest request) {
+    return "OK";
+  }
+
+  @PostMapping(path = "/list/non-null-elements", consumes = MediaType.APPLICATION_JSON_VALUE)
+  public String listNonNull(@RequestBody KotlinModel.KotlinListNonNullRequest request) {
+    return "OK";
+  }
+
+  @PostMapping(path = "/list/nullable-elements", consumes = MediaType.APPLICATION_JSON_VALUE)
+  public String listNullableElements(
+      @RequestBody KotlinModel.KotlinListNullableElementsRequest request) {
+    return "OK";
+  }
+
+  @PostMapping(path = "/map/non-null-values", consumes = MediaType.APPLICATION_JSON_VALUE)
+  public String mapNonNull(@RequestBody KotlinModel.KotlinMapValueNonNullRequest request) {
+    return "OK";
+  }
+
+  @PostMapping(path = "/map/nullable-values", consumes = MediaType.APPLICATION_JSON_VALUE)
+  public String mapNullable(@RequestBody KotlinModel.KotlinMapValueNullableRequest request) {
+    return "OK";
+  }
+}