Set release or target/sourceCompatibility conditionally

Author: emlun

buildSrc/src/main/kotlin/project-convention-java.gradle.kts

@@ -13,7 +13,13 @@ tasks.withType(JavaCompile::class) {
     options.compilerArgs.add("-Xlint:deprecation")
     options.compilerArgs.add("-Xlint:unchecked")
     options.encoding = "UTF-8"
-    options.release.set(8)
+
+    if (JavaVersion.current().isJava9Compatible) {
+        options.release.set(8)
+    } else {
+        targetCompatibility = "1.8"
+        sourceCompatibility = "1.8"
+    }
 }
 
 tasks.withType(Test::class) {