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"
@@ -714,16 +719,18 @@ 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:${crossScalaVersion}"
@@ -738,7 +745,7 @@ trait BridgeModule extends MillPublishJavaModule with CrossScalaModule {
   def compilerBridgeIvyDeps: T[Agg[Dep]] = Agg(
     (if (ZincWorkerUtil.isScala3(crossScalaVersion))
        ivy"org.scala-lang:scala3-sbt-bridge:${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 +1,28 @@
+/** Usage
+
+> rm build.mill # remove any existing build file
+
+> git init .
+> git remote add -f origin https://github.com/scala/scala3-example-project.git
+> git checkout 853808c50601e88edaa7272bcfb887b96be0e22a
+
+> ./mill init
+converting sbt build
+Running the added `millInitExportBuild` sbt task to export the build
+converting module scala3-example-project
+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
+parsed config (v3.8.4): ...
+init completed, run "mill resolve _" to list available tasks
+
+> ./mill compile
+compiling 13 Scala sources to ...out/compile.dest/classes ...
+
+> ./mill test
+MySuite:
+  + example test that succeeds ...
+*/

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

@@ -0,0 +1,27 @@
+/** 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
+parsed config (v3.8.4): ...
+init completed, run "mill resolve _" to list available tasks
+
+> ./mill compile # You will have to further configure the `CrossScalaModule` for different Scala versions
+compiling 7 Scala sources and 3 Java sources to ...out/compile.dest/classes ...
+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 +1,198 @@
+package mill.integration
+
+import mill.constants.Util
+import mill.integration.MillInitSbtUtils.bumpSbtTo1107
+import mill.integration.MillInitUtils.*
+import utest.*
+
+object MillInitSbtUtils {
+  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
+
+  val scalaPlatforms = Seq("js", "jvm", "native")
+}
+
+object MillInitScala3ExampleProjectTests extends BuildGenTestSuite {
+  def tests: Tests = Tests {
+    /*
+    - 17 KB
+    - sbt 1.10.7
+     */
+    val url =
+      "https://github.com/scala/scala3-example-project/archive/853808c50601e88edaa7272bcfb887b96be0e22a.zip"
+
+    test - integrationTest(url)(
+      testMillInit(
+        _,
+        expectedCompileTasks =
+          Some(SplitResolvedTasks(successful = Seq("compile", "test.compile"), failed = Seq.empty)),
+        expectedTestTasks = Some(SplitResolvedTasks(successful = Seq("test"), failed = Seq.empty))
+      )
+    )
+  }
+}
+
+object MillInitSbtScalaCsv200Tests 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 =>
+      bumpSbtTo1107(tester.workspacePath)
+
+      // Cross-builds are not supported yet.
+      testMillInit(
+        tester,
+        expectedCompileTasks =
+          Some(SplitResolvedTasks(successful = Seq(), failed = Seq("compile", "test.compile"))),
+        expectedTestTasks = Some(SplitResolvedTasks(successful = Seq(), failed = Seq("test")))
+      )
+    }
+  }
+}
+
+object MillInitSbtScalaCsv136Tests 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)
+
+      testMillInit(
+        tester,
+        expectedCompileTasks =
+          Some(SplitResolvedTasks(successful = Seq("compile", "test.compile"), failed = Seq.empty)),
+        expectedTestTasks = Some(SplitResolvedTasks(successful = Seq("test"), failed = Seq.empty))
+      )
+    }
+  }
+}
+
+// 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)
+      /*
+      `multi1.compile` doesn't work well when Mill is run with JDK 17 and 21:
+      ```text
+      1 tasks failed
+      multi1.compile java.io.IOError: java.lang.RuntimeException: /packages cannot be represented as URI
+          java.base/jdk.internal.jrtfs.JrtPath.toUri(JrtPath.java:175)
+          scala.tools.nsc.classpath.JrtClassPath.asURLs(DirectoryClassPath.scala:183)
+          ...
+      ```
+      Passing a `jvmId` 11 doesn't work here.
+       */
+      writeMillJvmVersionTemurin11(workspacePath)
+
+      val submodules = Seq("common", "multi1", "multi2")
+      testMillInit(
+        tester,
+        expectedCompileTasks = Some(SplitResolvedTasks(
+          successful = Seq("compile") ++ submodules.flatMap(allCompileTasks),
+          failed = Seq.empty
+        )),
+        expectedTestTasks =
+          Some(SplitResolvedTasks(successful = submodules.map(testTask), failed = Seq.empty))
+      )
+    }
+  }
+}
+
+// relatively large libraries
+
+object MillInitSbtGatlingTests extends BuildGenTestSuite {
+  def tests: Tests = Tests {
+    /*
+    - 1.8 MB
+    - sbt 1.10.7
+     */
+    val url = "https://github.com/gatling/gatling/archive/refs/tags/v3.13.4.zip"
+
+    val submodules = Seq(
+      "gatling-app",
+      "gatling-benchmarks",
+      "gatling-charts",
+      "gatling-commons",
+      "gatling-core-java",
+      "gatling-core",
+      "gatling-http-client",
+      "gatling-http-java",
+      "gatling-http",
+      "gatling-jdbc-java",
+      "gatling-jdbc",
+      "gatling-jms-java",
+      "gatling-jms",
+      "gatling-jsonpath",
+      "gatling-netty-util",
+      "gatling-quicklens",
+      "gatling-recorder",
+      "gatling-redis-java",
+      "gatling-redis",
+      "gatling-samples",
+      "gatling-test-framework"
+    )
+    val submodulesWithoutTests = Seq(
+      "gatling-app",
+      "gatling-benchmarks",
+      "gatling-quicklens",
+      "gatling-samples",
+      "gatling-test-framework"
+    )
+    val submodulesWithTests = submodules diff submodulesWithoutTests
+
+    test - integrationTest(url) { tester =>
+      testMillInit(
+        tester,
+        expectedCompileTasks = Some(SplitResolvedTasks(
+          all = Seq("compile")
+            ++ submodulesWithTests.flatMap(allCompileTasks)
+            ++ submodulesWithoutTests.map(compileTask),
+          failed = Seq(
+            /*
+            `...gatling-benchmarks/src/main/scala/io/gatling/Utils.scala:26:19: no arguments allowed for nullary method toString: (): String`
+            This fails to compile with sbt too. See https://github.com/gatling/gatling/issues/4612.
+             */
+            "gatling-benchmarks.compile"
+          )
+        )),
+        expectedTestTasks = Some(SplitResolvedTasks(
+          all = submodulesWithTests.map(testTask),
+          failed = Seq(
+            /*
+            `java.util.MissingResourceException: Can't find bundle for base name gatling-version, locale ...`
+            The version file in resources `gatling-commons/src/main/resources/gatling-version.properties`
+            is generated by a custom sbt task `generateVersionFileSettings`
+            and therefore missing after conversion.
+             */
+            //
+            "gatling-charts.test"
+          ) ++ (if (Util.isWindows)
+                  // This fails on Windows with sbt too.
+                  Seq("gatling-core.test")
+                else Seq.empty)
+        ))
+      )
+    }
+  }
+}