Ability to relocate/shade in assembly

build.sc

@@ -74,6 +74,7 @@ object Deps {
   val utest = ivy"com.lihaoyi::utest:0.7.4"
   val zinc = ivy"org.scala-sbt::zinc:1.4.0-M1"
   val bsp = ivy"ch.epfl.scala:bsp4j:2.0.0-M4"
+  val jarjarabrams = ivy"com.eed3si9n.jarjarabrams::jarjar-abrams-core:0.3.0"
 }
 
 trait MillPublishModule extends PublishModule{
@@ -167,7 +168,8 @@ object main extends MillModule {
       // Necessary so we can share the JNA classes throughout the build process
       Deps.jna,
       Deps.jnaPlatform,
-      Deps.coursier
+      Deps.coursier,
+      Deps.jarjarabrams
     )
 
     def generatedSources = T {

docs/pages/2 - Configuring Mill.md

@@ -513,7 +513,7 @@ compilation output, but if there is more than one or the main class comes from
 some library you can explicitly specify which one to use. This also adds the
 main class to your `foo.jar` and `foo.assembly` jars.
 
-## Merge/exclude files from assembly
+## Merge/exclude/relocate files from assembly
 
 When you make a runnable jar of your project with `assembly` command,
 you may want to exclude some files from a final jar (like signature files, and manifest files from library jars),
@@ -532,7 +532,8 @@ object foo extends ScalaModule {
   def assemblyRules = Seq(
     Rule.Append("application.conf"), // all application.conf files will be concatenated into single file
     Rule.AppendPattern(".*\\.conf"), // all *.conf files will be concatenated into single file
-    Rule.ExcludePattern("*.temp") // all *.temp files will be excluded from a final jar
+    Rule.ExcludePattern("*.temp"), // all *.temp files will be excluded from a final jar
+    Rule.Relocate("shapeless.**", "shade.shapless.@1") // the `shapeless` package will be shaded under the `shade` package
   )
 }
 ```

main/src/modules/Assembly.scala

@@ -1,11 +1,13 @@
 package mill.modules
 
-import java.io.InputStream
+import com.eed3si9n.jarjarabrams.{ShadePattern, Shader}
+import java.io.{ByteArrayInputStream, InputStream}
 import java.util.jar.JarFile
 import java.util.regex.Pattern
 import mill.Agg
 import os.Generator
 import scala.collection.JavaConverters._
+import scala.tools.nsc.io.Streamable
 
 object Assembly {
 
@@ -30,6 +32,8 @@ object Assembly {
 
     case class Exclude(path: String) extends Rule
 
+    case class Relocate(from: String, to: String) extends Rule
+
     object ExcludePattern {
       def apply(pattern: String): ExcludePattern = ExcludePattern(Pattern.compile(pattern))
     }
@@ -74,20 +78,35 @@ object Assembly {
     }
   }
 
-  def loadClasspath(
-    inputPaths: Agg[os.Path]
+  def loadShadedClasspath(
+    inputPaths: Agg[os.Path],
+    assemblyRules: Seq[Assembly.Rule]
   ): Generator[(String, UnopenedInputStream)] = {
+    val shadeRules = assemblyRules.collect {
+      case Rule.Relocate(from, to) => ShadePattern.Rename(List(from -> to)).inAll
+    }
+    val shader =
+      if (shadeRules.isEmpty) (name: String, inputStream: UnopenedInputStream) => Some(name -> inputStream)
+      else {
+        val shader = Shader.bytecodeShader(shadeRules, verbose = false)
+        (name: String, inputStream: UnopenedInputStream) =>
+          shader(Streamable.bytes(inputStream()), name).map {
+            case (bytes, name) =>
+              name -> (() => new ByteArrayInputStream(bytes) { override def close(): Unit = inputStream().close() })
+          }
+      }
+
     Generator.from(inputPaths).filter(os.exists).flatMap { path =>
       if (os.isFile(path)) {
         val jarFile = new JarFile(path.toIO)
         Generator.from(jarFile.entries().asScala.filterNot(_.isDirectory))
-          .map(entry => entry.getName -> (() => jarFile.getInputStream(entry)))
+          .flatMap(entry => shader(entry.getName, () => jarFile.getInputStream(entry)))
       }
       else {
         os.walk
           .stream(path)
           .filter(os.isFile)
-          .map(subPath => subPath.relativeTo(path).toString -> (() => os.read.inputStream(subPath)))
+          .flatMap(subPath => shader(subPath.relativeTo(path).toString, () => os.read.inputStream(subPath)))
       }
     }
   }

main/src/modules/Jvm.scala

@@ -286,7 +286,7 @@ object Jvm {
     manifest.build.write(manifestOut)
     manifestOut.close()
 
-    val mappings = Assembly.loadClasspath(inputPaths)
+    val mappings = Assembly.loadShadedClasspath(inputPaths, assemblyRules)
     Assembly.groupAssemblyEntries(mappings, assemblyRules).foreach {
       case (mapping, entry) =>
         val path = zipFs.getPath(mapping).toAbsolutePath

scalalib/test/resources/hello-world-deps/core/src/Main.scala

@@ -0,0 +1,13 @@
+import akka.http.scaladsl.model.{ContentTypes, HttpEntity}
+import akka.http.scaladsl.server.Directives._
+
+object Main extends App {
+  val route =
+    path("hello") {
+      get {
+        complete(HttpEntity(ContentTypes.`text/html(UTF-8)`, "<h1>Say hello to akka-http</h1>"))
+      }
+    }
+
+  println(route)
+}

scalalib/test/src/HelloWorldTests.scala

@@ -87,6 +87,14 @@ object HelloWorldTests extends TestSuite {
     }
   }
 
+  object HelloWorldAkkaHttpRelocate extends HelloBase {
+    object core extends HelloWorldModuleWithMain {
+      def ivyDeps = akkaHttpDeps
+
+      def assemblyRules = Seq(Assembly.Rule.Relocate("akka.**", "shaded.akka.@1"))
+    }
+  }
+
   object HelloWorldAkkaHttpNoRules extends HelloBase {
     object core extends HelloWorldModuleWithMain {
       def ivyDeps = akkaHttpDeps
@@ -684,9 +692,7 @@ object HelloWorldTests extends TestSuite {
               referenceContent.contains("Akka Stream Reference Config File"),
               // our application config is present too
               referenceContent.contains("My application Reference Config File"),
-              referenceContent.contains(
-                """akka.http.client.user-agent-header="hello-world-client""""
-              )
+              referenceContent.contains("""akka.http.client.user-agent-header="hello-world-client"""")
             )
           }
 
@@ -767,6 +773,34 @@ object HelloWorldTests extends TestSuite {
           resourcePath = helloWorldMultiResourcePath
         )
 
+        def checkRelocate[M <: TestUtil.BaseModule](module: M,
+                                                   target: Target[PathRef],
+                                                   resourcePath: os.Path = resourcePath
+                                                  ) =
+          workspaceTest(module, resourcePath) { eval =>
+            val Right((result, _)) = eval.apply(target)
+
+            val jarFile = new JarFile(result.path.toIO)
+
+            assert(!jarEntries(jarFile).contains("akka/http/scaladsl/model/HttpEntity.class"))
+            assert(jarEntries(jarFile).contains("shaded/akka/http/scaladsl/model/HttpEntity.class"))
+          }
+
+        'relocate - {
+          'withDeps - checkRelocate(
+            HelloWorldAkkaHttpRelocate,
+            HelloWorldAkkaHttpRelocate.core.assembly
+          )
+
+          'run - workspaceTest(
+            HelloWorldAkkaHttpRelocate,
+            resourcePath = os.pwd / 'scalalib / 'test / 'resources / "hello-world-deps"
+          ) { eval =>
+            val Right((_, evalCount)) = eval.apply(HelloWorldAkkaHttpRelocate.core.runMain("Main"))
+            assert(evalCount > 0)
+          }
+        }
+
         'writeDownstreamWhenNoRule - {
           'withDeps - workspaceTest(HelloWorldAkkaHttpNoRules) { eval =>
             val Right((result, _)) = eval.apply(HelloWorldAkkaHttpNoRules.core.assembly)