feat: add setting to choose preferred build server

metals/src/main/scala/scala/meta/internal/builds/BuildTool.scala

@@ -34,6 +34,12 @@ trait BuildTool {
  */
  def buildServerName = executableName
 
+ def possibleBuildServerNames: List[String] = List(buildServerName)
+
+ def isBspGenerated(workspace: AbsolutePath): Boolean =
+ possibleBuildServerNames
+ .map(name => workspace.resolve(".bsp").resolve(s"$name.json"))
+ .exists(_.isFile)
 }
 
 object BuildTool {

metals/src/main/scala/scala/meta/internal/builds/ScalaCliBuildTool.scala

@@ -61,13 +61,13 @@ class ScalaCliBuildTool(
 
  override val forcesBuildServer = true
 
- def isBspGenerated(workspace: AbsolutePath): Boolean =
- ScalaCliBuildTool.pathsToScalaCliBsp(workspace).exists(_.isFile)
+ override def possibleBuildServerNames = ScalaCli.names.toList
 
 }
 
 object ScalaCliBuildTool {
  def name = "scala-cli"
+
  def pathsToScalaCliBsp(root: AbsolutePath): List[AbsolutePath] =
  ScalaCli.names.toList.map(name =>
  root.resolve(".bsp").resolve(s"$name.json")

metals/src/main/scala/scala/meta/internal/metals/MetalsLspService.scala

@@ -2091,23 +2091,25 @@ class MetalsLspService(
  buildTool: Option[BuildTool.Found],
  chosenBuildServer: Option[String],
  ): Future[BuildChange] = {
- val isBloopOrEmpty = chosenBuildServer.isEmpty || chosenBuildServer.exists(
+ val preferredList =
+ userConfig.preferredBuildServes.map(_.trim().toLowerCase())
+ def isPreferredAboveBloop(buildServer: String) = {
+ val idx = preferredList.indexOf(buildServer)
+ if (idx >= 0) {
+ val bloopIdx = preferredList.indexOf("bloop")
+ bloopIdx < 0 || bloopIdx > idx
+ } else false
+ }
+ def isBloop = chosenBuildServer.exists(
  _ == BloopServers.name
  )
+
  buildTool match {
  case Some(BuildTool.Found(buildTool: BloopInstallProvider, digest))
- if isBloopOrEmpty =>
+ if isBloop || (chosenBuildServer.isEmpty && !isPreferredAboveBloop(
+ buildTool.buildServerName
+ )) =>
  slowConnectToBloopServer(forceImport, buildTool, digest)
- case Some(BuildTool.Found(buildTool: ScalaCliBuildTool, _))
- if !buildTool.isBspGenerated(folder) =>
- tables.buildServers.chooseServer(buildTool.buildServerName)
- buildTool
- .generateBspConfig(
- folder,
- args => bspConfigGenerator.runUnconditionally(buildTool, args),
- statusBar,
- )
- .flatMap(_ => quickConnectToBuildServer())
  // If there is no .bazelbsp present, we ask user to write bsp config
  // After that, we should fall into the last case and index workspace
  case Some(BuildTool.Found(_: BazelBuildTool, _))
@@ -2122,12 +2124,26 @@ class MetalsLspService(
  forceImport,
  )
  .flatMap(_ => quickConnectToBuildServer())
+ case Some(BuildTool.Found(buildTool: BuildServerProvider, _))
+ if !buildTool.isBspGenerated(folder) =>
+ tables.buildServers.chooseServer(buildTool.buildServerName)
+ buildTool
+ .generateBspConfig(
+ folder,
+ args => bspConfigGenerator.runUnconditionally(buildTool, args),
+ statusBar,
+ )
+ .flatMap(_ => quickConnectToBuildServer())
  case Some(BuildTool.Found(buildTool, _))
  if !chosenBuildServer.exists(
  _ == buildTool.buildServerName
  ) && buildTool.forcesBuildServer =>
  tables.buildServers.chooseServer(buildTool.buildServerName)
  quickConnectToBuildServer()
+ case Some(BuildTool.Found(buildTool: BloopInstallProvider, _))
+ if chosenBuildServer.isEmpty =>
+ tables.buildServers.chooseServer(buildTool.buildServerName)
+ quickConnectToBuildServer()
  case Some(found) =>
  indexer.reloadWorkspaceAndIndex(
  forceImport,

metals/src/main/scala/scala/meta/internal/metals/UserConfiguration.scala

@@ -56,6 +56,7 @@ case class UserConfiguration(
  verboseCompilation: Boolean = false,
  automaticImportBuild: AutoImportBuildKind = AutoImportBuildKind.Off,
  scalaCliLauncher: Option[String] = None,
+ preferredBuildServes: List[String] = Nil,
 ) {
 
  def currentBloopVersion: String =
@@ -349,6 +350,19 @@ object UserConfiguration {
  |only automatically import a build when a project is first opened, "all" will automate 
  |build imports after subsequent changes as well.""".stripMargin,
  ),
+ UserConfigurationOption(
+ "preferred-build-servers",
+ "[]",
+ """["sbt"]""",
+ "List of preferred build servers.",
+ """|If multiple build servers available, this list provides an order,
+ |that overrides the default partial order, in which the build server should be chosen.
+ |The default partial order is:
+ |1. `bloop`
+ |2. other build servers (asks user)
+ |3. fallback `scala-cli` (if no build server found)
+ |""".stripMargin,
+ ),
  )
 
  def fromJson(
@@ -570,6 +584,11 @@ object UserConfiguration {
  case _ => AutoImportBuildKind.Off
  }
 
+ val scalaCliLauncher = getStringKey("scala-cli-launcher")
+
+ val preferredBuildServes =
+ getStringListKey("preferred-build-servers").getOrElse(Nil)
+
  if (errors.isEmpty) {
  Right(
  UserConfiguration(
@@ -602,6 +621,8 @@ object UserConfiguration {
  customProjectRoot,
  verboseCompilation,
  autoImportBuilds,
+ scalaCliLauncher,
+ preferredBuildServes,
  )
  )
  } else {

tests/slow/src/test/scala/tests/PreferredBuildServer.scala

@@ -0,0 +1,71 @@
+package tests
+
+import scala.meta.internal.metals.UserConfiguration
+import scala.meta.internal.metals.{BuildInfo => V}
+
+class PreferredBuildServer extends BaseLspSuite("preferred-build-server") {
+ override def userConfig: UserConfiguration =
+ super.userConfig.copy(preferredBuildServes = List("sbt"))
+
+ test("start-sbt-when-preferred-no-bsp") {
+ cleanWorkspace()
+
+ val fileLayout =
+ s"""|/project/build.properties
+ |sbt.version=${V.sbtVersion}
+ |/build.sbt
+ |${SbtBuildLayout.commonSbtSettings}
+ |ThisBuild / scalaVersion := "${V.scala213}"
+ |val a = project.in(file("a"))
+ |/a/src/main/scala/a/A.scala
+ |package a
+ |object A {
+ | val a = 1
+ |}
+ |""".stripMargin
+ FileLayout.fromString(fileLayout, workspace)
+
+ for {
+ _ <- server.initialize()
+ _ <- server.initialized()
+ _ <- server.server.buildServerPromise.future
+ _ = assertNoDiff(
+ server.server.tables.buildServers.selectedServer().get,
+ "sbt",
+ )
+ _ = assert(server.server.bspSession.exists(_.main.isSbt))
+ } yield ()
+ }
+
+ test("start-sbt-when-preferred-with-bsp") {
+ cleanWorkspace()
+
+ val fileLayout =
+ s"""|/project/build.properties
+ |sbt.version=${V.sbtVersion}
+ |/build.sbt
+ |${SbtBuildLayout.commonSbtSettings}
+ |ThisBuild / scalaVersion := "${V.scala213}"
+ |val a = project.in(file("a"))
+ |/a/src/main/scala/a/A.scala
+ |package a
+ |object A {
+ | val a = 1
+ |}
+ |""".stripMargin
+
+ FileLayout.fromString(fileLayout, workspace)
+ SbtServerInitializer.generateBspConfig(workspace, V.sbtVersion)
+
+ for {
+ _ <- server.initialize()
+ _ <- server.initialized()
+ _ <- server.server.buildServerPromise.future
+ _ = assertNoDiff(
+ server.server.tables.buildServers.selectedServer().get,
+ "sbt",
+ )
+ _ = assert(server.server.bspSession.exists(_.main.isSbt))
+ } yield ()
+ }
+}

tests/unit/src/main/scala/tests/BuildServerInitializer.scala

@@ -133,7 +133,7 @@ object SbtServerInitializer extends BuildServerInitializer {
  }
  }
 
- private def generateBspConfig(
+ def generateBspConfig(
  workspace: AbsolutePath,
  sbtVersion: String,
  ): Unit = {