Prefer Class-File API on Java 24 or above

Author: Goooler

build.gradle.kts

@@ -4,9 +4,11 @@ import org.gradle.api.plugins.JavaPlugin.API_ELEMENTS_CONFIGURATION_NAME
 import org.gradle.api.plugins.JavaPlugin.JAVADOC_ELEMENTS_CONFIGURATION_NAME
 import org.gradle.api.plugins.JavaPlugin.RUNTIME_ELEMENTS_CONFIGURATION_NAME
 import org.gradle.api.plugins.JavaPlugin.SOURCES_ELEMENTS_CONFIGURATION_NAME
+import org.gradle.language.base.plugins.LifecycleBasePlugin.VERIFICATION_GROUP
 import org.gradle.plugin.compatibility.compatibility
 import org.jetbrains.kotlin.gradle.dsl.JvmDefaultMode
 import org.jetbrains.kotlin.gradle.dsl.JvmTarget
+import org.jetbrains.kotlin.gradle.dsl.KotlinJvmCompilerOptions
 import org.jetbrains.kotlin.gradle.dsl.KotlinVersion
 import org.jetbrains.kotlin.gradle.dsl.abi.ExperimentalAbiValidation
 
@@ -46,6 +48,8 @@ kotlin {
   }
 }
 
+addMultiReleaseSourceSet(24)
+
 lint {
   baseline = file("gradle/lint-baseline.xml")
   ignoreTestFixturesSources = true
@@ -240,6 +244,10 @@ buildConfig {
   }
 }
 
+tasks.jar {
+  manifest.attributes("Multi-Release" to true)
+}
+
 tasks.pluginUnderTestMetadata { pluginClasspath.from(testPluginClasspath) }
 
 tasks.check { dependsOn(tasks.withType<Test>()) }
@@ -254,3 +262,35 @@ tasks.clean {
       rootDir.resolve("site"),
     )
 }
+
+fun addMultiReleaseSourceSet(version: Int) {
+  kotlin.target.compilations.create("java${version}") {
+    associateWith(kotlin.target.compilations.getByName("main"))
+    compileTaskProvider {
+      compilerOptions {
+        this@compilerOptions as KotlinJvmCompilerOptions
+        jvmTarget = JvmTarget.fromTarget(version.toString())
+        freeCompilerArgs.add("-Xjdk-release=$version")
+      }
+    }
+    compileJavaTaskProvider { options.release = version }
+
+    tasks.jar { from(output.allOutputs) { into("META-INF/versions/$version") } }
+
+    val versionedTest =
+      tasks.register("testJava${version}", Test::class) {
+        useJUnitPlatform()
+        group = VERIFICATION_GROUP
+        description = "Runs test suite using Java $version toolchain."
+        val testSourceSet = sourceSets.test.get()
+        testClassesDirs = testSourceSet.output.classesDirs
+        val testCpWithoutMainOutput = testSourceSet.runtimeClasspath - sourceSets.main.get().output
+        // Prefer MR classes on the classpath, so remove main output.
+        classpath = files(tasks.jar.flatMap { it.archiveFile }) + testCpWithoutMainOutput
+        javaLauncher = javaToolchains.launcherFor {
+          languageVersion = JavaLanguageVersion.of(version)
+        }
+      }
+    tasks.check { dependsOn(versionedTest) }
+  }
+}

gradle.properties

@@ -2,6 +2,11 @@
 # https://kotlinlang.org/docs/gradle-configure-project.html#dependency-on-the-standard-library
 kotlin.stdlib.default.dependency=false
 
+# Keep associated Kotlin compilations from depending on archive tasks (e.g., jar), which can create circular task graphs in multi-release setups.
+# https://kotlinlang.org/docs/gradle-configure-project.html#disable-use-of-artifact-in-compilation-task
+# https://kotlinlang.org/docs/whatsnew2020.html#added-task-dependency-for-rare-cases-when-the-compile-task-lacks-one-on-an-artifact
+kotlin.build.archivesTaskOutputAsFriendModule=false
+
 org.gradle.caching=true
 org.gradle.configuration-cache=true
 org.gradle.configuration-cache.parallel=true

settings.gradle.kts

@@ -12,7 +12,10 @@ pluginManagement {
   }
 }
 
-plugins { id("com.gradle.develocity") version "4.5.0" }
+plugins {
+  id("com.gradle.develocity") version "4.5.0"
+  id("org.gradle.toolchains.foojay-resolver-convention") version "1.0.0"
+}
 
 develocity {
   buildScan {