Support mill init from an existing sbt project

.github/actions/post-build-setup/action.yml

@@ -34,4 +34,6 @@ runs:
         name: ${{ inputs.os }}-selective-execution-artifact
 
     - run: mv out/mill-selective-execution/mill-selective-execution.json out/mill-selective-execution.json
-      shell: bash
+      shell: bash
+
+    - uses: sbt/setup-sbt@v1

.github/actions/pre-build-setup/action.yml

@@ -65,4 +65,4 @@ runs:
     - uses: actions/checkout@v4
 
     - run: echo temurin:${{ inputs.java-version }} > .mill-jvm-version
-      shell: bash
+      shell: bash

.github/workflows/autofix.yml

@@ -7,6 +7,8 @@ jobs:
     steps:
       - uses: actions/checkout@v4
 
+      - uses: sbt/setup-sbt@v1
+
       - run: |
           ./mill __.fix + mill.javalib.palantirformat.PalantirFormatModule/ + mill.scalalib.scalafmt.ScalafmtModule/ + mill.kotlinlib.ktlint.KtlintModule/
           ./mill --meta-level 1 mill.scalalib.scalafmt.ScalafmtModule/

build.mill

@@ -53,8 +53,11 @@ object Deps {
   // and then add to it `bridgeScalaVersions`
   val scalaVersion = "3.6.2"
   val scala2Version = "2.13.15"
+  // The Scala 2.12.x version
+  val scalaVersion212 = "2.12.20"
   // The Scala 2.12.x version to use for some workers
-  val workerScalaVersion212 = "2.12.20"
+  val workerScalaVersion212 = scalaVersion212
+  val sbtScalaVersion212 = scalaVersion212
 
   val testScala213Version = "2.13.15"
   // Scala Native 4.2 will not get releases for new Scala version
@@ -194,7 +197,8 @@ object Deps {
   val sourcecode = ivy"com.lihaoyi::sourcecode:0.4.3-M5"
   val upickle = ivy"com.lihaoyi::upickle:4.1.0"
   val windowsAnsi = ivy"io.github.alexarchambault.windows-ansi:windows-ansi:0.0.6"
-  val zinc = ivy"org.scala-sbt::zinc:1.10.7".withDottyCompat(scalaVersion)
+  val sbtVersion = "1.10.7"
+  val zinc = ivy"org.scala-sbt::zinc:$sbtVersion".withDottyCompat(scalaVersion)
   // keep in sync with doc/antora/antory.yml
   val bsp4j = ivy"ch.epfl.scala:bsp4j:2.2.0-M2"
   val fansi = ivy"com.lihaoyi::fansi:0.5.0"
@@ -220,6 +224,7 @@ object Deps {
     ivy"org.apache.maven.resolver:maven-resolver-transport-wagon:$mavenResolverVersion"
   val coursierJvmIndexVersion = "0.0.4-84-f852c6"
   val gradleApi = ivy"dev.gradleplugins:gradle-api:8.11.1"
+  val sbt = ivy"org.scala-sbt:sbt:$sbtVersion"
 
   object RuntimeDeps {
     val dokkaVersion = "2.0.0"
@@ -713,16 +718,18 @@ trait MillStableScalaModule extends MillPublishScalaModule with Mima {
   }
 }
 
+trait MillPublishCrossScalaModule extends MillPublishJavaModule with CrossScalaModule
+
 object bridge extends Cross[BridgeModule](compilerBridgeScalaVersions)
-trait BridgeModule extends MillPublishJavaModule with CrossScalaModule {
+trait BridgeModule extends MillPublishCrossScalaModule {
   def scalaVersion = crossScalaVersion
   def publishVersion = bridgeVersion
   def artifactName = "mill-scala-compiler-bridge"
   def pomSettings = commonPomSettings(artifactName())
   def crossFullScalaVersion = true
   def ivyDeps = Agg(
-    ivy"org.scala-sbt:compiler-interface:${Deps.zinc.version}",
-    ivy"org.scala-sbt:util-interface:${Deps.zinc.version}"
+    ivy"org.scala-sbt:compiler-interface:${Deps.sbtVersion}",
+    ivy"org.scala-sbt:util-interface:${Deps.sbtVersion}"
   ) ++ Agg(
     if (ZincWorkerUtil.isScala3(crossScalaVersion))
       ivy"org.scala-lang::scala3-compiler:${crossScalaVersion}"
@@ -737,7 +744,7 @@ trait BridgeModule extends MillPublishJavaModule with CrossScalaModule {
   def compilerBridgeIvyDeps: T[Agg[Dep]] = Agg(
     (if (ZincWorkerUtil.isScala3(crossScalaVersion))
        ivy"org.scala-lang:scala3-sbt-bridge:${crossScalaVersion}"
-     else ivy"org.scala-sbt::compiler-bridge:${Deps.zinc.version}").exclude("*" -> "*")
+     else ivy"org.scala-sbt::compiler-bridge:${Deps.sbtVersion}").exclude("*" -> "*")
   )
 
   def compilerBridgeSourceJars: T[Agg[PathRef]] = Task {

dist/package.mill

@@ -75,6 +75,7 @@ object `package` extends RootModule with InstallModule {
       build.main.graphviz.testDep(),
       build.main.init.maven.testDep(),
       build.main.init.gradle.testDep(),
+      build.main.init.sbt.testDep(),
       build.scalalib.backgroundwrapper.testDep(),
       build.contrib.bloop.testDep(),
       build.contrib.buildinfo.testDep(),

example/package.mill

@@ -64,6 +64,7 @@ object `package` extends RootModule with Module {
     object web extends Cross[ExampleCrossModule](build.listIn(millSourcePath / "web"))
     object native extends Cross[ExampleCrossModule](build.listIn(millSourcePath / "native"))
     object spark extends Cross[ExampleCrossModule](build.listIn(millSourcePath / "spark"))
+    object migrating extends Cross[ExampleCrossModule](build.listIn(millSourcePath / "migrating"))
   }
   object javascriptlib extends Module {
     object basic extends Cross[ExampleCrossModule](build.listIn(millSourcePath / "basic"))

example/scalalib/migrating/1-sbt-complete/build.mill

@@ -0,0 +1,23 @@
+/** Usage
+
+> rm build.mill # remove any existing build file
+
+> git init .
+> git remote add -f origin https://github.com/scalacenter/library-example.git
+> git checkout v1.0.1
+
+> ./mill init
+converting module library-example
+Dependency Dependency(com.lightbend.paradox,paradox-theme-generic,false,0.4.4,Some(paradox-theme)) with an unknown configuration "paradox-theme" is dropped.
+Dependency Dependency(com.lightbend.paradox,paradox-theme-generic,false,0.4.4,Some(paradox-theme)) with an unknown configuration "paradox-theme" is dropped.
+generated 1 Mill build file(s)
+removing existing Mill build files
+writing Mill build file to build.mill
+converted sbt build to Mill
+formatting Mill build files
+Formatting 1 Scala sources
+init completed, run "mill resolve _" to list available tasks
+
+> ./mill compile
+done compiling
+*/

example/scalalib/migrating/2-sbt-incomplete/build.mill

@@ -0,0 +1,25 @@
+/** Usage
+
+> rm build.mill # remove any existing build file
+
+> git init .
+> git remote add -f origin https://github.com/tototoshi/scala-csv.git
+> git checkout 2.0.0
+
+> ./mill init
+converting sbt build
+Running the added `millInitExportBuild` sbt task to export the build
+converting module scala-csv
+generated 1 Mill build file(s)
+removing existing Mill build files
+writing Mill build file to build.mill
+converted sbt build to Mill
+formatting Mill build files
+Formatting 1 Scala sources
+init completed, run "mill resolve _" to list available tasks
+
+> ./mill compile # You will have to further configure the `CrossScalaModule` for different Scala versions
+error: class CSVReader protected (private val lineReader: LineReader)(implicit format: CSVFormat) extends Closeable with CSVReaderCompat {
+error:                                                                                                                   ^
+error: one error found
+*/

integration/feature/init/src/MillInitSbtTests.scala

@@ -0,0 +1,230 @@
+package mill.integration
+
+import mill.integration.MillInitSbtTests.{bumpSbtTo1107, initCommand}
+import utest.*
+
+object MillInitSbtTests {
+  val initCommand = ("init", "--base-module", "BaseModule", "--deps-object", "Deps", "--merge")
+  def bumpSbtTo1107(workspacePath: os.Path) =
+    // bump sbt version to resolve compatibility issues with lower sbt versions and higher JDK versions
+    os.write.over(workspacePath / "project" / "build.properties", "sbt.version = 1.10.7")
+}
+
+// relatively small libraries
+
+object MillInitLibraryExampleTests extends BuildGenTestSuite {
+  def tests: Tests = Tests {
+    /*
+    - 21 KB
+    - sbt 1.5.2
+     */
+    val url = "https://github.com/scalacenter/library-example/archive/refs/tags/v1.0.1.zip"
+
+    test - integrationTest(url) { tester =>
+      import tester.*
+
+      val initResult = eval(initCommand, stdout = os.Inherit, stderr = os.Inherit)
+      assert(initResult.isSuccess)
+
+      val compileResult = eval("compile")
+      assert(compileResult.isSuccess)
+    }
+  }
+}
+
+object MillInitScalaCsv200Tests extends BuildGenTestSuite {
+  def tests: Tests = Tests {
+    /*
+    - 34 KB
+    - originally sbt 1.10.0
+     */
+    val url = "https://github.com/tototoshi/scala-csv/archive/refs/tags/2.0.0.zip"
+
+    test - integrationTest(url) { tester =>
+      import tester.*
+
+      bumpSbtTo1107(workspacePath)
+
+      val initResult = eval(initCommand, stdout = os.Inherit, stderr = os.Inherit)
+      assert(initResult.isSuccess)
+
+      val compileResult = eval("compile")
+      // Cross builds are not supported yet.
+      assert(!compileResult.isSuccess)
+    }
+  }
+}
+
+object MillInitScalaCsv136Tests extends BuildGenTestSuite {
+  def tests: Tests = Tests {
+    /*
+    - 28 KB
+    - originally sbt 1.2.8
+     */
+    val url = "https://github.com/tototoshi/scala-csv/archive/refs/tags/1.3.6.zip"
+
+    test - integrationTest(url) { tester =>
+      import tester.*
+
+      bumpSbtTo1107(workspacePath)
+
+      val initResult = eval(initCommand, stdout = os.Inherit, stderr = os.Inherit)
+      assert(initResult.isSuccess)
+
+      val compileResult = eval("compile")
+      // It works here, but scala 2.11 with JDK 6 seems not supported when run with JDK 17 in shell.
+      assert(compileResult.isSuccess)
+    }
+  }
+}
+
+// same as the one in the unit tests
+object MillInitSbtMultiProjectExampleTests extends BuildGenTestSuite {
+  def tests: Tests = Tests {
+    /*
+    - 12 KB
+    - originally sbt 1.0.2
+     */
+    val url =
+      "https://github.com/pbassiner/sbt-multi-project-example/archive/152b31df9837115b183576b0080628b43c505389.zip"
+
+    test - integrationTest(url) { tester =>
+      import tester.*
+
+      bumpSbtTo1107(workspacePath)
+
+      val initResult = eval(initCommand, stdout = os.Inherit, stderr = os.Inherit)
+      assert(initResult.isSuccess)
+
+      val compileResult = eval("compile")
+      assert(compileResult.isSuccess)
+
+      val compileSubmodulesResult = eval("_.compile")
+      if (System.getProperty("java.version").split('.').head.toInt <= 11)
+        assert(compileSubmodulesResult.isSuccess)
+      else
+        // Submodules don't compile well with JDK 17 and 21, which seems to be due to incompatible bytecode versions in dependencies.
+        assert(!compileSubmodulesResult.isSuccess)
+    }
+  }
+}
+
+// relatively large libraries
+
+object MillInitZioHttpTests extends BuildGenTestSuite {
+  def tests: Tests = Tests {
+    /*
+    - 1.4 MB
+    - originally sbt 1.10.0
+     */
+    val url = "https://github.com/zio/zio-http/archive/refs/tags/v3.0.1.zip"
+
+    test - integrationTest(url) { tester =>
+      import tester.*
+
+      bumpSbtTo1107(workspacePath)
+
+      val initResult = eval(initCommand, stdout = os.Inherit, stderr = os.Inherit)
+      assert(initResult.isSuccess)
+
+      val compileResult = eval("compile")
+      assert(compileResult.isSuccess)
+
+      val compileSubmodulesResult = eval("_.compile")
+      // Some dependencies with currently unsupported `CrossVersion` `For3Use2_13` are not imported properly
+      assert(!compileSubmodulesResult.isSuccess)
+    }
+  }
+}
+
+// Scala.js and scala-native projects are not properly imported
+object MillInitSbtScalazTests extends BuildGenTestSuite {
+  def tests: Tests = Tests {
+    /*
+    - 0.8 MB
+    - sbt 1.9.7
+     */
+    val url = "https://github.com/scalaz/scalaz/archive/refs/tags/v7.3.8.zip"
+
+    test - integrationTest(url) { tester =>
+      import tester.*
+
+      os.call(("chmod", "+x", "sbt"), cwd = workspacePath)
+
+      val initResult = eval(initCommand, stdout = os.Inherit, stderr = os.Inherit)
+      assert(initResult.isSuccess)
+
+      val compileResult = eval("compile")
+      assert(compileResult.isSuccess)
+    }
+  }
+}
+
+// Scala.js and scala-native projects are not properly imported
+object MillInitSbtCatsTests extends BuildGenTestSuite {
+  def tests: Tests = Tests {
+    /*
+    - 1.9 MB
+    - sbt 1.10.7
+    - MUnit
+     */
+    val url = "https://github.com/typelevel/cats/archive/refs/tags/v2.13.0.zip"
+
+    test - integrationTest(url) { tester =>
+      import tester.*
+
+      val initResult = eval(initCommand, stdout = os.Inherit, stderr = os.Inherit)
+      assert(initResult.isSuccess)
+
+      val compileResult = eval("compile")
+      assert(compileResult.isSuccess)
+    }
+  }
+}
+
+// Converting child projects nested in a parent directory which is not a project is not supported yet.
+object MillInitSbtPlayFrameworkTests extends BuildGenTestSuite {
+  def tests: Tests = Tests {
+    // Commented out as it causes `java.util.concurrent.TimeoutException: Future timed out after [600000 milliseconds]` in the CI.
+    /*
+    /*
+    - 4.8 MB
+    - sbt 1.10.5
+     */
+    val url = "https://github.com/playframework/playframework/archive/refs/tags/3.0.6.zip"
+
+    test - integrationTest(url) { tester =>
+      import tester.*
+
+      val initResult = eval(initCommand, stdout = os.Inherit, stderr = os.Inherit)
+      assert(initResult.isSuccess)
+
+      val compileResult = eval("compile")
+      assert(compileResult.isSuccess)
+    }
+     */
+  }
+}
+
+// Scala.js and scala-native projects are not properly imported
+object MillInitSbtScalaCheckTests extends BuildGenTestSuite {
+  def tests: Tests = Tests {
+    /*
+    - 245 KB
+    - originally sbt 1.10.1
+     */
+    val url = "https://github.com/typelevel/scalacheck/archive/refs/tags/v1.18.1.zip"
+
+    test - integrationTest(url) { tester =>
+      import tester.*
+
+      bumpSbtTo1107(workspacePath)
+
+      val initResult = eval(initCommand, stdout = os.Inherit, stderr = os.Inherit)
+      assert(initResult.isSuccess)
+
+      val compileResult = eval("compile")
+      assert(compileResult.isSuccess)
+    }
+  }
+}