Add gradle debug plugin

build.gradle

@@ -13,6 +13,7 @@ buildscript {
 }
 
 plugins {
+  id "datadog.gradle-debug"
   id "datadog.dependency-locking"
 
   id "com.diffplug.spotless" version "6.13.0"

buildSrc/build.gradle.kts

@@ -5,6 +5,12 @@ plugins {
   id("com.diffplug.spotless") version "6.13.0"
 }
 
+java {
+  toolchain {
+    languageVersion = JavaLanguageVersion.of(8)
+  }
+}
+
 gradlePlugin {
   plugins {
     create("instrument-plugin") {

buildSrc/src/main/kotlin/datadog.gradle-debug.gradle.kts

@@ -0,0 +1,108 @@
+/*
+ * Gradle debugging plugin for dd-trace-java builds.
+ */
+
+val ddGradleDebugEnabled = project.hasProperty("ddGradleDebug")
+val logPath = rootProject.layout.buildDirectory.file("datadog.gradle-debug.log")
+
+fun inferJdkFromJavaHome(javaHome: String?): String {
+  val effectiveJavaHome = javaHome ?: System.getenv("JAVA_HOME")
+  if (effectiveJavaHome == null) {
+    throw IllegalStateException("JAVA_HOME is not set")
+  }
+  val javaExecutable = File(effectiveJavaHome, "bin/java").absolutePath
+  return try {
+    val process = ProcessBuilder(javaExecutable, "-version")
+        .redirectErrorStream(true)
+        .start()
+    val output = process.inputStream.bufferedReader().readText()
+    val versionLine = output.lines().firstOrNull() ?: ""
+    val versionMatch = Regex("version\\s+\"([0-9._]+)\"").find(versionLine)
+    versionMatch?.let {
+        val version = it.groupValues[1]
+        when {
+            version.startsWith("1.") -> version.substring(2, 3)
+            else -> version.split('.').first()
+        }
+    } ?: "unknown"
+  } catch (e: Exception) {
+    "error: ${e.message}"
+  }
+}
+
+fun getJdkFromCompilerOptions(co: CompileOptions): String? {
+  if (co.isFork) {
+    val fo = co.forkOptions
+    val javaHome = fo.javaHome
+    if (javaHome != null) {
+      return inferJdkFromJavaHome(javaHome.toString())
+    }
+  }
+  return null
+}
+
+fun printJdkForProjectTasks(project: Project, logFile: File) {
+  project.tasks.forEach { task ->
+    val data = mutableMapOf<String, String>()
+    data["task"] = task.path.toString()
+    if (task is JavaExec) {
+      val launcher = task.javaLauncher.get()
+      data["jdk"] = launcher.metadata.languageVersion.toString()
+    } else if (task is Javadoc) {
+      val tool = task.javadocTool.get()
+      data["jdk"] = tool.metadata.languageVersion.toString()
+    } else if (task is Test) {
+      val launcher = task.javaLauncher.get()
+      data["jdk"] = launcher.metadata.languageVersion.toString()
+    } else if (task is Exec) {
+      val java_home = task.environment.get("JAVA_HOME")?.toString()
+      data["jdk"] = inferJdkFromJavaHome(java_home)
+    } else if (task is JavaCompile) {
+      val compiler = task.javaCompiler.get()
+      data["jdk"] = compiler.metadata.languageVersion.toString()
+      val jdkFromJavaHome = getJdkFromCompilerOptions(task.options)
+      if (jdkFromJavaHome != null && jdkFromJavaHome != data["jdk"]) {
+        data["java_home"] = jdkFromJavaHome
+      }
+    } else if (task is GroovyCompile) {
+      val launcher = task.javaLauncher.get()
+      data["jdk"] = launcher.metadata.languageVersion.toString()
+      val jdkFromJavaHome = getJdkFromCompilerOptions(task.options)
+      if (jdkFromJavaHome != null && jdkFromJavaHome != data["jdk"]) {
+        data["java_home"] = jdkFromJavaHome
+      }
+    } else if (task is ScalaCompile) {
+      val launcher = task.javaLauncher.get()
+      data["jdk"] = launcher.metadata.languageVersion.toString()
+      val jdkFromJavaHome = getJdkFromCompilerOptions(task.options)
+      if (jdkFromJavaHome != null && jdkFromJavaHome != data["jdk"]) {
+        data["java_home"] = jdkFromJavaHome
+      }
+    } else {
+      data["jdk"] = "unknown"
+    }
+    val json = data.entries.joinToString(prefix = "{", postfix = "}") { (k, v) -> "\"$k\":\"$v\"" }
+    logFile.appendText("$json\n")
+  }
+}
+
+class DebugBuildListener : org.gradle.BuildListener {
+  override fun settingsEvaluated(settings: Settings) = Unit
+
+  override fun projectsLoaded(gradle: Gradle) = Unit
+
+  override fun buildFinished(result: BuildResult) = Unit
+
+  override fun projectsEvaluated(gradle: Gradle) {
+    val logFile = logPath.get().asFile
+    logFile.writeText("")
+    gradle.rootProject.allprojects.forEach { project ->
+        printJdkForProjectTasks(project, logFile)
+    }
+  }
+}
+
+if (ddGradleDebugEnabled) {
+  logger.lifecycle("datadog.gradle-debug plugin is enabled")
+  gradle.addListener(DebugBuildListener())
+}