Add GenerateEmbeddedJreTask to generate JRE (#740)

* Add GenerateEmbeddedJreTask to create custom JRE

Introduced GenerateEmbeddedJreTask for generating a trimmed JRE using jlink. Added task registration in setupTasks to facilitate custom JRE creation during the build process. This helps minimize the bundled JRE size tailored to specific needs.

* Move registration out of after evaluate

* Improve task api and update docs

* Update task to fix deprecations and address review comments

* Ensure java home from task execution is used

Author: chippmann

docs/src/doc/user-guide/exporting.md

@@ -51,6 +51,26 @@ by using `jlink` with rosetta and an amd64 JDK on an arm64 MacOS.
     For desktop exports you need to make exports based on the platform you're on, as exporting will copy the generated jre folder to
     your export. An MacOS JRE will not work on Windows, so you'll need a Windows host to export for Windows.
 
+Alternatively we provide a configurable gradle task which generates the JRE for your current host OS:
+`./gradlew generateEmbeddedJre`
+
+The task can be configured like so:
+```kotlin
+tasks.withType<GenerateEmbeddedJreTask> {
+    // the values in this example are the default values of the task
+    this.javaHome = System.getProperty("java.home") // path to your java home dir
+    this.arguments = arrayOf(
+        "--strip-debug",
+        "--no-header-files",
+        "--no-man-pages",
+    ) // arguments to pass to the jlink command
+    this.modules = arrayOf(
+        "java.base",
+        "java.logging",
+    ) // java module to include in the jre
+}
+```
+
 ## Specifics
 
 `godot-bootstrap.jar` and `main.jar` are copied into `pck` during the export process.

kt/plugins/godot-gradle-plugin/src/main/kotlin/godot/gradle/projectExt/setupTasks.kt

@@ -1,5 +1,6 @@
 package godot.gradle.projectExt
 
+import godot.gradle.tasks.GenerateEmbeddedJreTask
 import godot.gradle.tasks.android.checkAndroidJarAccessibleTask
 import godot.gradle.tasks.android.checkD8ToolAccessibleTask
 import godot.gradle.tasks.android.createBootstrapDexJarTask
@@ -24,6 +25,11 @@ import godot.gradle.tasks.setupCleanTask
 import org.gradle.api.Project
 
 fun Project.setupTasks() {
+    tasks.register("generateEmbeddedJre", GenerateEmbeddedJreTask::class.java) { task ->
+        task.group = "godot-kotlin-jvm"
+        task.description = "Generates an embedded jre using jlink"
+    }
+
     afterEvaluate {
         with(it) {
             val packageBootstrapJarTask = packageBootstrapJarTask()

kt/plugins/godot-gradle-plugin/src/main/kotlin/godot/gradle/tasks/GenerateEmbeddedJreTask.kt

@@ -0,0 +1,74 @@
+package godot.gradle.tasks
+
+import godot.tools.common.constants.Paths
+import org.gradle.api.DefaultTask
+import org.gradle.api.tasks.Input
+import org.gradle.api.tasks.TaskAction
+import org.gradle.process.ExecOperations
+import java.io.File
+import java.util.*
+import javax.inject.Inject
+
+open class GenerateEmbeddedJreTask @Inject constructor(
+    private val execOperations: ExecOperations,
+) : DefaultTask() {
+
+    @Input
+    var modules: Array<String> = arrayOf(
+        "java.base",
+        "java.logging",
+    )
+
+    @Input
+    var outputDir: String = "${Paths.GODOT_KOTLIN_JVM_DIR}/jre-${getArch()}-${getOs()}"
+
+    @Input
+    var arguments: Array<String> = arrayOf(
+        "--strip-debug",
+        "--no-header-files",
+        "--no-man-pages"
+    )
+
+    @Input
+    var javaHome: String? = null
+
+    @TaskAction
+    fun createJre() {
+        File(outputDir).deleteRecursively()
+
+        val resolvedJavaHome = javaHome ?: System.getProperty("java.home")
+
+        execOperations.exec { spec ->
+            spec.commandLine(
+                "$resolvedJavaHome/bin/jlink",
+                "--add-modules", modules.joinToString(","),
+                "--output", outputDir,
+                *arguments,
+            )
+        }
+
+        logger.lifecycle(
+            "Custom JRE created in $outputDir using modules: '${modules.joinToString(",")}', arguments: '${
+                arguments.joinToString(" ")
+            }' and java home: $resolvedJavaHome"
+        )
+    }
+
+    private fun getArch(): String {
+        return when (val arch = System.getProperty("os.arch")) {
+            "aarch64", "arm64" -> "arm64"
+            "x86_64", "amd64" -> "amd64"
+            else -> throw IllegalArgumentException("Unsupported host architecture: $arch")
+        }
+    }
+
+    private fun getOs(): String {
+        val os = System.getProperty("os.name").lowercase(Locale.US)
+        return when {
+            os.contains("mac", true) -> "macos"
+            os.contains("nix", true) || os.contains("nux", true) || os.contains("aix", true) -> "linux"
+            os.contains("win", true) -> "windows"
+            else -> throw IllegalArgumentException("Unsupported host operating system: $os")
+        }
+    }
+}