Error Prone / NullAway support for JSpecify - added Kotlin

build.gradle

@@ -1,3 +1,6 @@
+import org.jetbrains.kotlin.gradle.dsl.JvmTarget
+import org.jetbrains.kotlin.gradle.dsl.KotlinVersion
+import net.ltgt.gradle.errorprone.CheckSeverity
 import java.text.SimpleDateFormat
 
 plugins {
@@ -12,6 +15,9 @@ plugins {
     id 'com.github.ben-manes.versions' version '0.51.0'
     id "me.champeau.jmh" version "0.7.3"
     id "net.ltgt.errorprone" version '4.2.0'
+
+    // Kotlin just for tests - not
+    id 'org.jetbrains.kotlin.jvm' version '2.1.21'
 }
 
 java {
@@ -20,6 +26,19 @@ java {
     }
 }
 
+kotlin {
+    compilerOptions {
+        apiVersion = KotlinVersion.KOTLIN_2_0
+        languageVersion = KotlinVersion.KOTLIN_2_0
+        jvmTarget = JvmTarget.JVM_11
+        javaParameters = true
+        freeCompilerArgs = [
+                '-Xemit-jvm-type-annotations',
+                '-Xjspecify-annotations=strict',
+        ]
+    }
+}
+
 def getDevelopmentVersion() {
     def output = new StringBuilder()
     def error = new StringBuilder()
@@ -79,9 +98,10 @@ dependencies {
 
     errorprone 'com.uber.nullaway:nullaway:0.12.6'
     errorprone 'com.google.errorprone:error_prone_core:2.37.0'
-}
 
-import net.ltgt.gradle.errorprone.CheckSeverity
+    // just tests
+    testCompileOnly 'org.jetbrains.kotlin:kotlin-stdlib-jdk8'
+}
 
 tasks.withType(JavaCompile) {
     options.release = 11

src/main/java/org/dataloader/DataLoader.java

@@ -68,7 +68,7 @@
  */
 @PublicApi
 @NullMarked
-public class DataLoader<K, V> {
+public class DataLoader<K, V extends @Nullable Object> {
 
     private final @Nullable String name;
     private final DataLoaderHelper<K, V> helper;

src/test/kotlin/org/dataloader/KotlinExamples.kt

@@ -0,0 +1,39 @@
+package org.dataloader
+
+import org.junit.jupiter.api.Test
+import java.util.concurrent.CompletableFuture
+
+/**
+ * Some Kotlin code to prove that are JSpecify annotations work here
+ * as expected in Kotlin land.  We don't intend to ue Kotlin in our tests
+ * or to deliver Kotlin code in the java
+ */
+class KotlinExamples {
+
+    @Test
+    fun `basic kotlin test of non nullable value types`() {
+        val dataLoader: DataLoader<String, String> = DataLoaderFactory.newDataLoader { keys -> CompletableFuture.completedFuture(keys.toList()) }
+
+        val cfA = dataLoader.load("A")
+        val cfB = dataLoader.load("B")
+
+        dataLoader.dispatch()
+
+        cfA.join().equals("A")
+        cfB.join().equals("B")
+    }
+
+    @Test
+    fun `basic kotlin test of nullable value types`() {
+        val dataLoader: DataLoader<String, String?> = DataLoaderFactory.newDataLoader { keys -> CompletableFuture.completedFuture(keys.toList()) }
+
+        val cfA = dataLoader.load("A")
+        val cfB = dataLoader.load("B")
+
+        dataLoader.dispatch()
+
+        cfA.join().equals("A")
+        cfB.join().equals("B")
+    }
+
+}