Add Java version check

paperweight-core/src/main/kotlin/io/papermc/paperweight/core/PaperweightCore.kt

@@ -42,6 +42,7 @@ import org.gradle.kotlin.dsl.*
 
 class PaperweightCore : Plugin<Project> {
     override fun apply(target: Project) {
+        checkJavaVersion()
         Git.checkForGit()
 
         val ext = target.extensions.create(PAPERWEIGHT_EXTENSION, PaperweightCoreExtension::class, target)

paperweight-lib/src/main/kotlin/io/papermc/paperweight/util/utils.kt

@@ -32,6 +32,7 @@ import io.papermc.paperweight.util.constants.*
 import java.io.File
 import java.io.InputStream
 import java.io.OutputStream
+import java.lang.management.ManagementFactory
 import java.lang.reflect.Type
 import java.net.URI
 import java.net.URL
@@ -317,3 +318,29 @@ fun FileCollection.toJarClassProviderRoots(): List<ClassProviderRoot> =
         .filter { p -> p.isLibraryJar }
         .map { p -> ClassProviderRoot.fromJar(p) }
         .toList()
+
+private fun javaVersion(): Int {
+    val version = System.getProperty("java.specification.version")
+    val parts = version.split("\\.".toRegex()).dropLastWhile { it.isEmpty() }.toTypedArray()
+    val errorMsg = "Could not determine version of the current JVM"
+    check(parts.isNotEmpty()) { errorMsg }
+    return if (parts[0] == "1") {
+        check(parts.size >= 2) { errorMsg }
+        parts[1].toInt()
+    } else {
+        parts[0].toInt()
+    }
+}
+
+fun checkJavaVersion() {
+    val minimumJava = 11
+    val ver = javaVersion()
+    if (ver < minimumJava) {
+        var msg = "paperweight requires Gradle to be run with a Java $minimumJava runtime or newer."
+        val runtimeMX = ManagementFactory.getRuntimeMXBean()
+        if (runtimeMX != null) {
+            msg += " Current runtime: Java ${runtimeMX.specVersion} (${runtimeMX.vmName} ${runtimeMX.vmVersion})"
+        }
+        throw PaperweightException(msg)
+    }
+}

paperweight-patcher/src/main/kotlin/io/papermc/paperweight/patcher/PaperweightPatcher.kt

@@ -48,6 +48,7 @@ import org.gradle.kotlin.dsl.registering
 class PaperweightPatcher : Plugin<Project> {
 
     override fun apply(target: Project) {
+        checkJavaVersion()
         Git.checkForGit()
 
         val patcher = target.extensions.create(PAPERWEIGHT_EXTENSION, PaperweightPatcherExtension::class, target)

paperweight-userdev/src/main/kotlin/io/papermc/paperweight/userdev/PaperweightUser.kt

@@ -65,6 +65,8 @@ abstract class PaperweightUser : Plugin<Project> {
     abstract val javaToolchainService: JavaToolchainService
 
     override fun apply(target: Project) {
+        checkJavaVersion()
+
         val sharedCacheRootRoot = target.gradle.gradleUserHomeDir.toPath().resolve("caches/paperweight-userdev")
         val sharedCacheRoot = if (target.sharedCaches) {
             logger.lifecycle("paperweight-userdev experimental shared caches are enabled.")