Migrate codegen to be a plugin (#3401)

buildSrc/src/main/kotlin/io/opentelemetry/instrumentation/gradle/codegen/ClasspathByteBuddyPlugin.kt

@@ -0,0 +1,72 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+package io.opentelemetry.instrumentation.gradle.codegen
+
+import net.bytebuddy.ByteBuddy
+import net.bytebuddy.build.Plugin
+import net.bytebuddy.description.type.TypeDescription
+import net.bytebuddy.dynamic.ClassFileLocator
+import net.bytebuddy.dynamic.DynamicType
+import java.io.File
+import java.net.URL
+import java.net.URLClassLoader
+
+/**
+ * Starting from version 1.10.15, ByteBuddy gradle plugin transformations require that plugin
+ * classes are given as class instances instead of a class name string. To be able to still use a
+ * plugin implementation that is not a buildscript dependency, this reimplements the previous logic
+ * by taking a delegate class name and class path as arguments and loading the plugin class from the
+ * provided classloader when the plugin is instantiated.
+ */
+class ClasspathByteBuddyPlugin(
+  classPath: Iterable<File>, sourceDirectory: File, className: String
+) : Plugin {
+  private val delegate = pluginFromClassPath(classPath, sourceDirectory, className)
+
+  override fun apply(
+    builder: DynamicType.Builder<*>,
+    typeDescription: TypeDescription,
+    classFileLocator: ClassFileLocator
+  ): DynamicType.Builder<*> {
+    return delegate.apply(builder, typeDescription, classFileLocator)
+  }
+
+  override fun close() {
+    delegate.close()
+  }
+
+  override fun matches(typeDefinitions: TypeDescription): Boolean {
+    return delegate.matches(typeDefinitions)
+  }
+
+  companion object {
+    private fun pluginFromClassPath(
+      classPath: Iterable<File>, sourceDirectory: File, className: String
+    ): Plugin {
+      val classLoader = classLoaderFromClassPath(classPath, sourceDirectory)
+      try {
+        val clazz = Class.forName(className, false, classLoader)
+        return clazz.getDeclaredConstructor().newInstance() as Plugin
+      } catch (e: Exception) {
+        throw IllegalStateException("Failed to create ByteBuddy plugin instance", e)
+      }
+    }
+
+    private fun classLoaderFromClassPath(
+      classPath: Iterable<File>, sourceDirectory: File
+    ): ClassLoader {
+      val urls = mutableListOf<URL>()
+      urls.add(fileAsUrl(sourceDirectory))
+      for (file in classPath) {
+        urls.add(fileAsUrl(file))
+      }
+      return URLClassLoader(urls.toTypedArray(), ByteBuddy::class.java.classLoader)
+    }
+
+    private fun fileAsUrl(file: File): URL {
+      return file.toURI().toURL()
+    }
+  }
+}

buildSrc/src/main/kotlin/io/opentelemetry/instrumentation/gradle/codegen/ClasspathTransformation.kt

@@ -0,0 +1,28 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+package io.opentelemetry.instrumentation.gradle.codegen
+
+import net.bytebuddy.build.Plugin.Factory.UsingReflection.ArgumentResolver
+import net.bytebuddy.build.gradle.Transformation
+import org.gradle.api.tasks.Classpath
+import org.gradle.api.tasks.Input
+import java.io.File
+
+/**
+ * Special implementation of [Transformation] is required as classpath argument must be
+ * exposed to Gradle via [Classpath] annotation, which cannot be done if it is returned by
+ * [Transformation.getArguments].
+ */
+class ClasspathTransformation(
+  @get:Classpath val classpath: Iterable<File>,
+  @get:Input val pluginClassName: String
+) : Transformation() {
+  override fun makeArgumentResolvers(): List<ArgumentResolver> {
+    return listOf(
+      ArgumentResolver.ForIndex(0, classpath),
+      ArgumentResolver.ForIndex(2, pluginClassName)
+    )
+  }
+}