Optimize embeddable JARs

Exclude the compiler dummy JAR from the resulting shadow JAR

buildSrc/src/main/kotlin/embeddable.kt

@@ -1,10 +1,8 @@
 @file:Suppress("unused") // usages in build scripts are not tracked properly
 
 import com.github.jengelman.gradle.plugins.shadow.tasks.ShadowJar
-import org.gradle.api.GradleException
 import org.gradle.api.Project
 import org.gradle.api.file.DuplicatesStrategy
-import org.gradle.api.tasks.bundling.Zip
 import org.gradle.jvm.tasks.Jar
 import org.gradle.kotlin.dsl.task
 import org.gradle.kotlin.dsl.*
@@ -104,23 +102,22 @@ fun Project.embeddableCompilerDummyForDependenciesRewriting(taskName: String = "
     }
 }
 
-fun Project.rewriteDepsToShadedJar(originalJarTask: Jar, shadowJarTask: Zip, body: Jar.() -> Unit = {}): Jar {
-    val originalFiles by lazy {
-        val jarContents = zipTree(originalJarTask.outputs.files.singleFile).files
-        val basePath = jarContents.find { it.name == "MANIFEST.MF" }?.parentFile?.parentFile ?: throw GradleException("cannot determine the jar root dir")
-        jarContents.map { it.relativeTo(basePath).path }.toSet()
+fun Project.rewriteDepsToShadedJar(originalJarTask: Jar, shadowJarTask: Jar, body: Jar.() -> Unit = {}): Jar {
+    originalJarTask.apply {
+        classifier = "original"
     }
-    return task<Jar>("rewrittenDepsJar") {
-        originalJarTask.apply {
-            classifier = "original"
-        }
-        shadowJarTask.apply {
-            dependsOn(originalJarTask)
-            from(originalJarTask)// { include("**") }
-            classifier = "shadow"
-        }
-        dependsOn(shadowJarTask)
-        from(project.zipTree(shadowJarTask.outputs.files.singleFile)) { include { originalFiles.any { originalFile -> it.file.canonicalPath.endsWith(originalFile) } } }
+
+    val compilerDummyJarFile by lazy { configurations.getAt("compilerDummyJar").singleFile }
+
+    return shadowJarTask.apply {
+        dependsOn(originalJarTask)
+        from(originalJarTask)// { include("**") }
+
+        // When Gradle traverses the inputs, reject the shaded compiler JAR,
+        // which leads to the content of that JAR being excluded as well:
+        exclude { it.file == compilerDummyJarFile }
+
+        classifier = null
         body()
     }
 }