Handle upcoming mill embedded BSP and fix mill BSP install

bsp/src/org/jetbrains/bsp/project/importing/BspProjectResolver.scala

@@ -171,9 +171,13 @@ class BspProjectResolver extends ExternalSystemProjectResolver[BspExecutionSetti
         case BspProjectSettings.AutoPreImport =>
           if (executionSettings.config == AutoConfig && bloopConfigDir(workspace).isDefined && isSbtProject)
             runBloopInstall(workspace)
+          else if (MillProjectImportProvider.canImport(workspace))
+            MillProjectImportProvider.bspInstall(workspace)
           else emptySuccess
         case BspProjectSettings.BloopSbtPreImport =>
           runBloopInstall(workspace)
+        case BspProjectSettings.MillBspPreImport =>
+          MillProjectImportProvider.bspInstall(workspace)
       }
     } else emptySuccess
   }

bsp/src/org/jetbrains/bsp/project/importing/MillProjectImportProvider.scala

@@ -0,0 +1,40 @@
+package org.jetbrains.bsp.project.importing
+
+import java.io.File
+import org.jetbrains.plugins.scala.build.BuildMessages
+import scala.io.Source
+import scala.sys.process._
+import scala.util.{Failure, Try, Using}
+
+object MillProjectImportProvider {
+  def canImport(workspace: File): Boolean =
+    Option(workspace) match {
+      case Some(directory) if directory.isDirectory => isBspCompatible(directory) || isLegacyBspCompatible(directory)
+      case _ => false
+    }
+
+  def bspInstall(workspace: File): Try[BuildMessages] = {
+    val work =
+      if (isBspCompatible(workspace)) Try(Process("./mill mill.bsp.BSP/install", workspace).!!)
+      else if (isLegacyBspCompatible(workspace)) Try(Process("./mill -i mill.contrib.BSP/install", workspace).!!)
+      else Failure(new IllegalStateException("Unable to install BSP as this is not a Mill project"))
+
+    work.transform(
+      _ => Try(BuildMessages.empty.status(BuildMessages.OK)),
+      e => Try(BuildMessages.empty.status(BuildMessages.Error).addError(e.getMessage))
+    )
+  }
+
+  private def isBspCompatible(workspace: File) = workspace.listFiles().exists { buildScript =>
+    !buildScript.isDirectory && buildScript.getName == "mill" &&
+      Using.resource(Source.fromFile(buildScript))(_.getLines().exists(!_.matches("""^.*(0\.8\.0|0\.7.+|0\.6.+)$""")))
+  }
+
+  // Legacy Mill =< 0.8.0
+  private def isLegacyBspCompatible(workspace: File) = workspace.listFiles().exists { buildScript =>
+    !buildScript.isDirectory && buildScript.getName == "build.sc" &&
+      Using.resource(Source.fromFile(buildScript))(
+        _.getLines().contains("import $ivy.`com.lihaoyi::mill-contrib-bsp:$MILL_VERSION`")
+      )
+  }
+}

bsp/src/org/jetbrains/bsp/project/importing/bspConfigSteps.scala

@@ -16,13 +16,13 @@ import org.jetbrains.annotations.Nls
 import org.jetbrains.bsp.{BspBundle, BspUtil}
 import org.jetbrains.bsp.project.importing.BspSetupConfigStep.ConfigSetupTask
 import org.jetbrains.bsp.project.importing.bspConfigSteps._
-import org.jetbrains.bsp.project.importing.setup.{BspConfigSetup, FastpassConfigSetup, MillConfigSetup, NoConfigSetup, SbtConfigSetup}
+import org.jetbrains.bsp.project.importing.setup.{BspConfigSetup, FastpassConfigSetup, NoConfigSetup, SbtConfigSetup}
 import org.jetbrains.bsp.protocol.BspConnectionConfig
 import org.jetbrains.bsp.settings.BspProjectSettings._
 import org.jetbrains.plugins.scala.build.IndicatorReporter
 import org.jetbrains.plugins.scala.project.Version
 import org.jetbrains.sbt.SbtUtil._
-import org.jetbrains.sbt.project.{MillProjectImportProvider, SbtProjectImportProvider}
+import org.jetbrains.sbt.project.SbtProjectImportProvider
 
 object bspConfigSteps {
 
@@ -104,8 +104,9 @@ object bspConfigSteps {
           // server config to be set in next step
           SbtConfigSetup(workspace)
         case bspConfigSteps.MillSetup =>
-          builder.setPreImportConfig(NoPreImport)
-          MillConfigSetup(workspace)
+          builder.setPreImportConfig(MillBspPreImport)
+          builder.setServerConfig(AutoConfig)
+          NoConfigSetup
         case bspConfigSteps.FastpassSetup =>
           builder.setPreImportConfig(NoPreImport)
           val bspWorkspace = FastpassConfigSetup.computeBspWorkspace(workspace)
@@ -129,7 +130,7 @@ object bspConfigSteps {
     } else Nil
 
     val millChoice =
-      if (MillProjectImportProvider.canImport(vfile)) List(MillSetup)
+      if (MillProjectImportProvider.canImport(vfile.toNioPath.toFile)) List(MillSetup)
       else Nil
 
     val bloopChoice =

bsp/src/org/jetbrains/bsp/project/importing/projectImport.scala

@@ -31,7 +31,7 @@ import org.jetbrains.bsp._
 import org.jetbrains.bsp.protocol.BspConnectionConfig
 import org.jetbrains.bsp.settings.BspProjectSettings._
 import org.jetbrains.bsp.settings._
-import org.jetbrains.sbt.project.{MillProjectImportProvider, SbtProjectImportProvider}
+import org.jetbrains.sbt.project.SbtProjectImportProvider
 
 class BspProjectImportBuilder
   extends AbstractExternalProjectImportBuilder[BspImportControl](
@@ -251,7 +251,8 @@ object BspProjectOpenProcessor {
     // val sbtProject = SbtProjectImportProvider.canImport(workspace)
     // temporarily disable sbt importing via bloop from welcome screen (SCL-17359)
     val sbtProject = false
-    val millProject = MillProjectImportProvider.canImport(workspace)
+
+    val millProject = MillProjectImportProvider.canImport(workspace.toNioPath.toFile)
 
     bspConnectionProtocolSupported || bloopProject || bspConnectionProtocolSupported || sbtProject || millProject
   }

bsp/src/org/jetbrains/bsp/protocol/BspCommunication.scala

@@ -34,7 +34,7 @@ class BspCommunication private[protocol](base: File, config: BspServerConfig) ex
 
   private val session: AtomicReference[Option[BspSession]] = new AtomicReference[Option[BspSession]](None)
 
-  val exitCommands: List[List[String]] = {
+  lazy val exitCommands: List[List[String]] = {
     val workspace = new File(base.getAbsolutePath)
     val files = BspConnectionConfig.workspaceBspConfigs(workspace)
     val argvExitCommands = files.flatMap { file =>

bsp/src/org/jetbrains/bsp/settings/settings.scala

@@ -71,20 +71,24 @@ object BspProjectSettings {
   case object AutoPreImport extends PreImportConfig
   /** Preimport with Bloop from sbt project */
   case object BloopSbtPreImport extends PreImportConfig
+  /** Preimport with BSP from Mill project */
+  case object MillBspPreImport extends PreImportConfig
 
   class PreImportConfigConverter extends Converter[PreImportConfig] {
     override def fromString(value: String): PreImportConfig =
       value match {
         case "NoPreImport" => NoPreImport
         case "AutoPreImport" => AutoPreImport
         case "BloopBspPreImport" => BloopSbtPreImport
+        case "MillBspPreImport" => MillBspPreImport
       }
 
     override def toString(value: PreImportConfig): String =
       value match {
         case NoPreImport => "NoPreImport"
         case AutoPreImport => "AutoPreImport"
         case BloopSbtPreImport => "BloopBspPreImport"
+        case MillBspPreImport => "MillBspPreImport"
       }
   }
 
@@ -101,7 +105,7 @@ object BspProjectSettings {
     override def toString(value: BspServerConfig): String =
       value match {
         case AutoConfig => "AutoConfig"
-        case BloopConfig =>"BloopConfig"
+        case BloopConfig => "BloopConfig"
         case BspConfigFile(path) => s"BspConfigFile:$path"
       }
   }