Extended mill init to support an existing Maven project

build.mill

@@ -182,6 +182,14 @@ object Deps {
   val sonatypeCentralClient = ivy"com.lumidion::sonatype-central-client-requests:0.3.0"
   val kotlinVersion = "2.0.21"
   val kotlinCompiler = ivy"org.jetbrains.kotlin:kotlin-compiler:$kotlinVersion"
+  val mavenVersion = "3.9.9"
+  val mavenEmbedder = ivy"org.apache.maven:maven-embedder:$mavenVersion"
+  val mavenResolverVersion = "1.9.22"
+  val mavenResolverConnectorBasic = ivy"org.apache.maven.resolver:maven-resolver-connector-basic:$mavenResolverVersion"
+  val mavenResolverSupplier = ivy"org.apache.maven.resolver:maven-resolver-supplier:$mavenResolverVersion"
+  val mavenResolverTransportFile = ivy"org.apache.maven.resolver:maven-resolver-transport-file:$mavenResolverVersion"
+  val mavenResolverTransportHttp = ivy"org.apache.maven.resolver:maven-resolver-transport-http:$mavenResolverVersion"
+  val mavenResolverTransportWagon = ivy"org.apache.maven.resolver:maven-resolver-transport-wagon:$mavenResolverVersion"
 
   object RuntimeDeps {
     val dokkaVersion = "1.9.20"

dist/package.mill

@@ -19,6 +19,7 @@ object `package` extends RootModule with build.MillPublishJavaModule {
 
     def testTransitiveDeps = build.runner.testTransitiveDeps() ++ Seq(
       build.main.graphviz.testDep(),
+      build.main.maven.testDep(),
       build.runner.linenumbers.testDep(),
       build.scalalib.backgroundwrapper.testDep(),
       build.contrib.bloop.testDep(),

integration/feature/init/src/MillInitMavenTests.scala

@@ -0,0 +1,221 @@
+package mill.integration
+
+import mill.testkit.{IntegrationTester, UtestIntegrationTestSuite}
+import utest._
+
+object MillInitMavenTests extends UtestIntegrationTestSuite {
+
+  private def prep[T](githubSourceZipUrl: String)(f: IntegrationTester => T): T = {
+    val zipFile = os.temp(requests.get(githubSourceZipUrl))
+    val unzipDir = os.unzip(zipFile, os.temp.dir())
+    val sourceDir = os.list(unzipDir).head
+
+    integrationTest { tester =>
+      for (p <- os.list(sourceDir)) os.move.into(p, tester.workspacePath)
+      f(tester)
+    }
+  }
+
+  def tests: Tests = Tests {
+
+    // - Junit5
+    // - maven-compiler-plugin release option
+    test("jansi") {
+      prep("https://github.com/fusesource/jansi/archive/refs/tags/jansi-2.4.1.zip") { tester =>
+        import tester._
+
+        val initRes = eval(("init", "--deps-object", "Deps"))
+        initRes.out.contains(
+          "generated 1 Mill build file(s)"
+        ) ==> true
+        initRes.isSuccess ==> true
+
+        val compileRes = eval("compile")
+        compileRes.err.contains(
+          "compiling 20 Java sources"
+        ) ==> true
+        compileRes.isSuccess ==> true
+
+        val testRes = eval("test")
+        testRes.out.contains(
+          "Test run finished: 0 failed, 1 ignored, 90 total"
+        ) ==> true
+        testRes.isSuccess ==> true
+
+        val publishLocalRes = eval("publishLocal")
+        publishLocalRes.err.contains(
+          "Publishing Artifact(org.fusesource.jansi,jansi,2.4.1)"
+        ) ==> true
+        publishLocalRes.isSuccess ==> true
+      }
+    }
+
+    // - multi-module
+    // - TestNg
+    // - maven-compiler-plugin release option
+    test("dotenv") {
+      prep("https://github.com/shyiko/dotenv/archive/refs/tags/0.1.1.zip") { tester =>
+        import tester._
+
+        val initRes = eval("init")
+        initRes.out.contains(
+          "generated 3 Mill build file(s)"
+        ) ==> true
+        initRes.isSuccess ==> true
+
+        val resolveRes = eval(("resolve", "_"))
+        Seq(
+          "dotenv",
+          "dotenv-guice"
+        ).forall(resolveRes.out.contains) ==> true
+
+        // JavaModule.JavaTests is not picking compileIvyDeps from outer module
+        val compileRes = eval("__.compile")
+        compileRes.err.contains("package com.google.inject does not exist") ==> true
+        compileRes.isSuccess ==> false
+
+        // even if compile error is fixed, TestNg version is not supported
+        // val testRes = eval("__.test")
+        // testRes.isSuccess ==> false
+      }
+    }
+
+    // - multi-module
+    // - Junit5
+    // - submodule e2e directory and artifact name differ
+    test("fastexcel") {
+      prep("https://github.com/dhatim/fastexcel/archive/refs/tags/0.18.4.zip") { tester =>
+        import tester._
+
+        val initRes = eval("init")
+        initRes.out.contains(
+          "generated 4 Mill build file(s)"
+        ) ==> true
+        initRes.isSuccess ==> true
+
+        val resolveRes = eval(("resolve", "_"))
+        Seq(
+          "fastexcel-reader",
+          "fastexcel-writer",
+          "e2e"
+        ).forall(resolveRes.out.contains) ==> true
+
+        // not sure why this happens but pom.xml has a hack to handle JPMS
+        val compileRes = eval("__.compile")
+        Seq(
+          "module not found: org.apache.commons.compress",
+          "module not found: com.fasterxml.aalto",
+          "module not found: opczip"
+        ).forall(compileRes.err.contains) ==> true
+        compileRes.isSuccess ==> false
+      }
+    }
+
+    // - multi-module
+    // - Junit5
+    // - build-helper-maven-plugin
+    // - maven-compiler-plugin compilerArgs options
+    // - submodule directory and artifact names differ
+    // - multi line description, property <argLine.common>
+    // - property <jetty.alpnAgent.path> contains quotes
+    test("netty") {
+      prep("https://github.com/netty/netty/archive/refs/tags/netty-4.1.114.Final.zip") { tester =>
+        import tester._
+
+        val initRes = eval(("init", "--publish-properties"))
+        // cannot resolve native dependencies defined by build extension os-maven-plugin
+        initRes.out.contains(
+          """[codec-http2] dropping classifier ${os.detected.classifier} for dependency io.netty:netty-tcnative:2.0.66.Final
+            |[transport-native-epoll] dropping classifier ${os.detected.classifier} for dependency io.netty:netty-tcnative:2.0.66.Final
+            |[transport-native-kqueue] dropping classifier ${os.detected.classifier} for dependency io.netty:netty-tcnative:2.0.66.Final
+            |[handler] dropping classifier ${os.detected.classifier} for dependency io.netty:netty-tcnative:2.0.66.Final
+            |[example] dropping classifier ${os.detected.classifier} for dependency io.netty:netty-tcnative:2.0.66.Final
+            |[testsuite] dropping classifier ${os.detected.classifier} for dependency io.netty:netty-tcnative:2.0.66.Final
+            |[testsuite-shading] dropping classifier ${os.detected.classifier} for dependency io.netty:netty-tcnative:2.0.66.Final
+            |[transport-blockhound-tests] dropping classifier ${os.detected.classifier} for dependency io.netty:netty-tcnative:2.0.66.Final
+            |[microbench] dropping classifier ${os.detected.classifier} for dependency io.netty:netty-tcnative:2.0.66.Final
+            |""".stripMargin
+        ) ==> true
+        initRes.out.contains(
+          "generated 47 Mill build file(s)"
+        ) ==> true
+        initRes.isSuccess ==> true
+
+        val resolveRes = eval(("resolve", "_"))
+        Seq(
+          "all",
+          "dev-tools",
+          "common",
+          "buffer",
+          "codec",
+          "codec-dns",
+          "codec-haproxy",
+          "codec-http",
+          "codec-http2",
+          "codec-memcache",
+          "codec-mqtt",
+          "codec-redis",
+          "codec-smtp",
+          "codec-socks",
+          "codec-stomp",
+          "codec-xml",
+          "resolver",
+          "resolver-dns",
+          "resolver-dns-classes-macos",
+          "resolver-dns-native-macos",
+          "transport",
+          "transport-native-unix-common-tests",
+          "transport-native-unix-common",
+          "transport-classes-epoll",
+          "transport-native-epoll",
+          "transport-classes-kqueue",
+          "transport-native-kqueue",
+          "transport-rxtx",
+          "transport-sctp",
+          "transport-udt",
+          "handler",
+          "handler-proxy",
+          "handler-ssl-ocsp",
+          "example",
+          "testsuite",
+          "testsuite-autobahn",
+          "testsuite-http2",
+          "testsuite-osgi",
+          "testsuite-shading",
+          "testsuite-native",
+          "testsuite-native-image",
+          "testsuite-native-image-client",
+          "testsuite-native-image-client-runtime-init",
+          "transport-blockhound-tests",
+          "microbench",
+          "bom"
+        ).forall(resolveRes.out.contains) ==> true
+
+        // additional sources defined by build-helper-maven-plugin
+        val sourcesRes = eval(("show", "transport-native-epoll.sources"))
+        Seq(
+          s"$workspacePath/transport-native-epoll/src/main/java",
+          s"$workspacePath/transport-native-epoll/src/main/c"
+        ).forall(sourcesRes.out.contains) ==> true
+
+        // compile succeeds for submodule
+        val compileRes = eval("codec.compile")
+        compileRes.err.contains(
+          "compiling 155 Java sources"
+        ) ==> true
+        compileRes.isSuccess ==> true
+
+        // test compile fails for submodule due to missing native dependency
+        val testRes = eval("codec.test")
+        testRes.err.contains(
+          "package io.netty.nativeimage does not exist"
+        ) ==> true
+        testRes.isSuccess ==> false
+
+        // publishLocal fails for submodule (due to several Javadoc errors)
+        val publishLocalRes = eval("codec.publishLocal")
+        publishLocalRes.isSuccess ==> false
+      }
+    }
+  }
+}

main/init/package.mill

@@ -4,7 +4,8 @@ import mill._
 import scala.util.matching.Regex
 
 object `package` extends RootModule with build.MillPublishScalaModule {
-  def moduleDeps = Seq(build.main)
+
+  def moduleDeps = Seq(build.main, build.scalalib)
 
   override def resources = Task {
     super.resources() ++ Seq(exampleList())

main/init/src/mill/init/InitMavenModule.scala

@@ -0,0 +1,95 @@
+package mill.init
+
+import coursier.LocalRepositories
+import coursier.maven.MavenRepository
+import mill.api.{Loose, PathRef}
+import mill.define.{Discover, ExternalModule, TaskModule}
+import mill.scalalib.scalafmt.ScalafmtWorkerModule
+import mill.util.{Jvm, Util}
+import mill.{Command, T, Task}
+
+import scala.util.control.NoStackTrace
+
+@mill.api.experimental
+object InitMavenModule extends ExternalModule with InitMavenModule with TaskModule {
+
+  lazy val millDiscover: Discover = Discover[this.type]
+}
+
+/**
+ * Defines a [[InitModule.init task]] to convert a Maven build to Mill.
+ */
+@mill.api.experimental
+trait InitMavenModule extends TaskModule {
+
+  def defaultCommandName(): String = "init"
+
+  /**
+   * Classpath containing [[buildGenMainClass build file generator]].
+   */
+  def buildGenClasspath: T[Loose.Agg[PathRef]] = T {
+    val repositories = Seq(
+      LocalRepositories.ivy2Local,
+      MavenRepository("https://repo1.maven.org/maven2"),
+      MavenRepository("https://oss.sonatype.org/content/repositories/releases")
+    )
+    Util.millProjectModule("mill-main-maven", repositories)
+  }
+
+  /**
+   * Mill build file generator application entrypoint.
+   */
+  def buildGenMainClass: T[String] = "mill.main.maven.BuildGen"
+
+  /**
+   * Scalafmt configuration file for formatting generated Mill build files.
+   */
+  def initScalafmtConfig: T[PathRef] = T {
+    val config = millSourcePath / ".scalafmt.conf"
+    if (!os.exists(config)) {
+      T.log.info(s"creating Scalafmt configuration file $config ...")
+      os.write(
+        config,
+        s"""version = "3.8.4-RC1"
+           |runner.dialect = scala213
+           |""".stripMargin
+      )
+    }
+    PathRef(config)
+  }
+
+  /**
+   * Generates and formats Mill build files for an existing Maven project.
+   *
+   * @param args arguments for the [[buildGenMainClass build file generator]]
+   */
+  def init(args: String*): Command[Unit] = Task.Command {
+    val root = millSourcePath
+
+    val mainClass = buildGenMainClass()
+    val classPath = buildGenClasspath().map(_.path)
+    val exit = Jvm.callSubprocess(
+      mainClass = mainClass,
+      classPath = classPath,
+      mainArgs = args,
+      workingDir = root
+    ).exitCode
+
+    if (exit == 0) {
+      val files = os.walk.stream(root, skip = (root / "out").equals)
+        .filter(_.ext == "mill")
+        .map(PathRef(_))
+        .toSeq
+      val config = initScalafmtConfig()
+      T.log.info("formatting Mill build files ...")
+      ScalafmtWorkerModule.worker().reformat(files, config)
+
+      T.log.info("init completed, run \"mill resolve _\" to list available tasks")
+    } else {
+      throw InitMavenException(s"$mainClass exit($exit)")
+    }
+  }
+}
+
+@mill.api.experimental
+case class InitMavenException(message: String) extends Exception(message) with NoStackTrace