Use jvmToolchain(8) for the plugin and runtime

Otherwise, if the project using kotlinx-benchmark is configured with an older jvmToolchain than the Java with which Gradle was launched to assemble plugin or runtime, the following error occurs:

Execution failed for task ':jvmBenchmarkGenerate'.
> There was a failure while executing work items
  > A failure occurred while executing kotlinx.benchmark.gradle.JmhBytecodeGeneratorWorker
    > kotlinx/benchmark/gradle/JmhBytecodeGeneratorWorkParameters has been compiled by a more recent version of the Java Runtime (class file version 61.0), this version of the Java Runtime only recognizes class file versions up to 52.0

Similar issue: #176

Author: Abduqodiri Qurbonzoda

integration/src/test/kotlin/kotlinx/benchmark/integration/JvmToolchainsTest.kt

@@ -6,9 +6,17 @@ import kotlin.test.assertEquals
 
 class JvmToolchainsTest : GradleTest() {
     @Test
-    fun testJvmToolchainSetup() {
-        val runner = project("kmp-with-toolchain", true, GradleTestVersion.v8_0) {
+    fun testHigherVersionThanInGradle() {
+        val runner = project("kmp-with-toolchain/higher-version-than-in-gradle", true, GradleTestVersion.v8_0)
+        runner.runAndSucceed("benchmark") {
+            assertEquals(TaskOutcome.SUCCESS, task(":jvmBenchmark")!!.outcome)
+            assertOutputDoesNotContain("<failure>")
         }
+    }
+
+    @Test
+    fun testMinSupportedVersion() {
+        val runner = project("kmp-with-toolchain/min-supported-version", true)
         runner.runAndSucceed("benchmark") {
             assertEquals(TaskOutcome.SUCCESS, task(":jvmBenchmark")!!.outcome)
             assertOutputDoesNotContain("<failure>")

integration/src/test/resources/templates/kmp-with-toolchain/build.gradle renamed to integration/src/test/resources/templates/kmp-with-toolchain/higher-version-than-in-gradle/build.gradle

@@ -0,0 +1,18 @@
+kotlin {
+    jvmToolchain(8)
+    jvm {}
+
+    sourceSets {
+        commonMain {
+            dependencies {
+                implementation("org.jetbrains.kotlinx:kotlinx-benchmark-runtime:0.5.0-SNAPSHOT")
+            }
+        }
+    }
+}
+
+benchmark {
+    targets {
+        register("jvm")
+    }
+}

integration/src/test/resources/templates/kmp-with-toolchain/gradle.properties renamed to integration/src/test/resources/templates/kmp-with-toolchain/higher-version-than-in-gradle/gradle.properties

@@ -0,0 +1 @@
+org.gradle.jvmargs=-Xmx2g -XX:+HeapDumpOnOutOfMemoryError -Dfile.encoding=UTF-8

integration/src/test/resources/templates/kmp-with-toolchain/settings.gradle renamed to integration/src/test/resources/templates/kmp-with-toolchain/higher-version-than-in-gradle/settings.gradle

@@ -0,0 +1,15 @@
+package test
+
+import kotlinx.benchmark.*
+import kotlin.math.*
+
+// Don't really need to measure anything here, just check that the benchmark works
+@State(Scope.Benchmark)
+@Warmup(iterations = 0)
+@Measurement(iterations = 1, time = 100, timeUnit = BenchmarkTimeUnit.MILLISECONDS)
+@OutputTimeUnit(BenchmarkTimeUnit.MILLISECONDS)
+@BenchmarkMode(Mode.Throughput)
+open class CommonBenchmark {
+    @Benchmark
+    open fun mathBenchmark() = 3.14
+}

integration/src/test/resources/templates/kmp-with-toolchain/src/commonMain/kotlin/CommonBenchmark.kt renamed to integration/src/test/resources/templates/kmp-with-toolchain/higher-version-than-in-gradle/src/commonMain/kotlin/CommonBenchmark.kt

@@ -86,11 +86,11 @@ sourceSets {
 }
 
 kotlin {
+    jvmToolchain(8)
+
     @OptIn(ExperimentalBuildToolsApi::class, ExperimentalKotlinGradlePluginApi::class)
     compilerVersion = libs.versions.kotlin.`for`.gradle.plugin.get()
-}
 
-tasks.compileKotlin {
     compilerOptions {
         optIn.addAll(
                 "kotlinx.benchmark.gradle.internal.KotlinxBenchmarkPluginInternalApi",

integration/src/test/resources/templates/kmp-with-toolchain/min-supported-version/build.gradle

@@ -12,6 +12,8 @@ repositories {
 }
 
 kotlin {
+    jvmToolchain(8)
+
     // According to https://kotlinlang.org/docs/native-target-support.html
 
     // Tier 1