chore: set Java LTS release for build script compilation

Previously the build failed if the default Java was newer than 20.

Now we explicitly specify jvmTarget for the build script compilation.

Note: it does not impact the target JVM for the resulting JMeter binaries.

build-logic-commons/gradle-plugin/build.gradle.kts

@@ -16,6 +16,8 @@
  */
 
 import org.gradle.kotlin.dsl.support.expectedKotlinDslPluginsVersion
+import org.jetbrains.kotlin.gradle.dsl.JvmTarget
+import org.jetbrains.kotlin.gradle.tasks.KotlinCompile
 
 plugins {
     `kotlin-dsl`
@@ -29,4 +31,25 @@ dependencies {
     // to make it work.
     // See https://github.com/gradle/gradle/issues/17016 regarding expectedKotlinDslPluginsVersion
     implementation("org.gradle.kotlin.kotlin-dsl:org.gradle.kotlin.kotlin-dsl.gradle.plugin:$expectedKotlinDslPluginsVersion")
+    // It seems to be the best way to make KotlinCompile available for use in build-logic.kotlin-dsl-gradle-plugin.gradle.kts
+    implementation("org.jetbrains.kotlin.jvm:org.jetbrains.kotlin.jvm.gradle.plugin:$embeddedKotlinVersion")
+}
+
+// We need to figure out a version that is supported by the current JVM, and by the Kotlin Gradle plugin
+val currentJava = JavaVersion.current()
+if (currentJava > JavaVersion.VERSION_1_8) {
+    // We want an LTS Java release for build script compilation
+    val latestSupportedLts = listOf("25", "21", "17", "11")
+        .intersect(JvmTarget.values().mapTo(mutableSetOf()) { it.target })
+        .first { JavaVersion.toVersion(it) <= currentJava }
+
+    tasks.withType<JavaCompile>().configureEach {
+        options.release.set(JavaVersion.toVersion(latestSupportedLts).majorVersion.toInt())
+    }
+
+    tasks.withType<KotlinCompile>().configureEach {
+        kotlinOptions {
+            jvmTarget = latestSupportedLts
+        }
+    }
 }

build-logic-commons/gradle-plugin/src/main/kotlin/build-logic.kotlin-dsl-gradle-plugin.gradle.kts

@@ -15,6 +15,9 @@
  * limitations under the License.
  */
 
+import org.jetbrains.kotlin.gradle.dsl.JvmTarget
+import org.jetbrains.kotlin.gradle.tasks.KotlinCompile
+
 plugins {
     id("java-library")
     id("org.gradle.kotlin.kotlin-dsl") // this is 'kotlin-dsl' without version
@@ -24,3 +27,21 @@ tasks.validatePlugins {
     failOnWarning.set(true)
     enableStricterValidation.set(true)
 }
+
+val currentJava = JavaVersion.current()
+if (currentJava > JavaVersion.VERSION_1_8) {
+    // We want an LTS Java release for build script compilation
+    val latestSupportedLts = listOf("25", "21", "17", "11")
+        .intersect(JvmTarget.values().mapTo(mutableSetOf()) { it.target })
+        .first { JavaVersion.toVersion(it) <= currentJava }
+
+    tasks.withType<JavaCompile>().configureEach {
+        options.release.set(JavaVersion.toVersion(latestSupportedLts).majorVersion.toInt())
+    }
+
+    tasks.withType<KotlinCompile>().configureEach {
+        kotlinOptions {
+            jvmTarget = latestSupportedLts
+        }
+    }
+}