refactor: Migrate Metals server to Scala 3

This mostly involved:
- changing imports
- moving things between MtagsEnrichements variants
- adding ()
- fixing bugs reported now as warning or errors (things previously not reported at all)

.scalafix.conf

@@ -1,19 +1,15 @@
 rules = [
-  OrganizeImports,
-  ExplicitResultTypes,
-  RemoveUnused
+  OrganizeImports
 ]
 
-ExplicitResultTypes.rewriteStructuralTypesToNamedSubclass = false
-
-RemoveUnused.imports = false
-
 OrganizeImports.groupedImports = Explode
 OrganizeImports.expandRelative = true
-OrganizeImports.removeUnused = true
+OrganizeImports.removeUnused = false
 OrganizeImports.groups = [
   "re:javax?\\."
   "scala."
   "scala.meta."
   "*"
 ]
+
+OrganizeImports.targetDialect = StandardLayout

.scalafix2.conf

@@ -0,0 +1,19 @@
+rules = [
+  OrganizeImports,
+  ExplicitResultTypes,
+  RemoveUnused
+]
+
+ExplicitResultTypes.rewriteStructuralTypesToNamedSubclass = false
+
+RemoveUnused.imports = false
+
+OrganizeImports.groupedImports = Explode
+OrganizeImports.expandRelative = true
+OrganizeImports.removeUnused = true
+OrganizeImports.groups = [
+  "re:javax?\\."
+  "scala."
+  "scala.meta."
+  "*"
+]

.scalafmt.conf

@@ -1,5 +1,5 @@
 version = "3.8.1"
-runner.dialect = scala213source3
+runner.dialect = scala3
 project.git = true
 align.preset = none
 align.stripMargin = true
@@ -37,6 +37,7 @@ fileOverride {
   },
   "glob:**/mtags*/**" {
     trailingCommas = never
+    runner.dialect = scala213
   }
   "glob:**/tests/cross/src/**" {
     trailingCommas = never

build.sbt

@@ -36,16 +36,16 @@ def crossSetting[A](
 logo := Welcome.logo
 usefulTasks := Welcome.tasks
 
-ThisBuild / scalafixScalaBinaryVersion := scalaBinaryVersion.value
+ThisBuild / scalafixScalaBinaryVersion := "2.13"
 
 inThisBuild(
   List(
     version ~= { dynVer =>
       if (isCI) dynVer
       else localSnapshotVersion // only for local publishing
     },
-    scalaVersion := V.scala213,
-    crossScalaVersions := List(V.scala213),
+    scalaVersion := V.scala3,
+    crossScalaVersions := List(V.scala3),
     organization := "org.scalameta",
     licenses := Seq(
       "Apache-2.0" -> url("http://www.apache.org/licenses/LICENSE-2.0")
@@ -128,7 +128,7 @@ commands ++= Seq(
       runMtagsPublishLocal(st, v, localSnapshotVersion)
     }
     "interfaces/publishLocal" ::
-      s"++${V.scala213} metals/publishLocal" ::
+      s"++${V.scala3} metals/publishLocal" ::
       "mtags-java/publishLocal" ::
       publishMtags
   },
@@ -218,6 +218,27 @@ val sharedSettings = sharedJavacOptions ++ sharedScalacOptions ++ List(
       )
     ),
   ),
+  excludeDependencies ++= crossSetting(
+    scalaVersion.value,
+    if3 = {
+      // Exclude cross published version dependencies leading to conflicts in Scala 3 vs 2.13
+      // When using Scala 3 exclude Scala 2.13 standard native libraries,
+      // when using Scala 2.13 exclude Scala 3 standard native libraries
+      // Use full name, Maven style published artifacts cannot use artifact/cross version for exclusion rules
+      List(
+        ExclusionRule()
+          .withOrganization("org.scala-lang.modules")
+          .withName(
+            "scala-collection-compat_2.13"
+          ),
+        ExclusionRule()
+          .withOrganization("org.scala-lang.modules")
+          .withName(
+            "scala-xml_2.13"
+          ),
+      )
+    },
+  ),
   scalacOptions ++= lintingOptions(scalaVersion.value),
 )
 
@@ -284,21 +305,19 @@ def multiScalaDirectories(root: File, scalaVersion: String) = {
   result.toList
 }
 
-def scala3ScalametaDependency =
-  ("org.scalameta" %% "scalameta" % V.scalameta)
-    .cross(CrossVersion.for3Use2_13)
-    .exclude("org.scala-lang", "scala-reflect")
-    .exclude("org.scala-lang", "scala-compiler")
-    // the correct one should be brought in by the scala 3 compiler
-    .exclude("org.scala-lang", "scala-library")
-    .exclude(
-      "com.lihaoyi",
-      "geny_2.13",
-    ) // avoid 2.13 and 3 on the classpath since we rely on it directly
-    .exclude(
-      "com.lihaoyi",
-      "sourcecode_2.13",
-    ) // avoid 2.13 and 3 on the classpath since it comes in via pprint
+def scalametaDependency = ("org.scalameta" %% "scalameta" % V.scalameta)
+  .cross(CrossVersion.for3Use2_13)
+  .exclude("org.scala-lang", "scala-reflect")
+  .exclude("org.scala-lang", "scala-compiler")
+  .exclude("org.scala-lang.modules", "scala-collection-compat")
+  .exclude(
+    "com.lihaoyi",
+    "geny_2.13",
+  ) // avoid 2.13 and 3 on the classpath since we rely on it directly
+  .exclude(
+    "com.lihaoyi",
+    "sourcecode_2.13",
+  )
 
 val mtagsSettings = List(
   crossScalaVersions := V.supportedScalaVersions,
@@ -331,7 +350,7 @@ val mtagsSettings = List(
       ),
       if3 = List(
         "org.scala-lang" %% "scala3-compiler" % scalaVersion.value,
-        scala3ScalametaDependency,
+        scalametaDependency,
       ),
     ),
   },
@@ -360,22 +379,22 @@ val mtagsSettings = List(
   },
 )
 
-lazy val mtags3 = project
+lazy val mtags2 = project
   .in(file(".mtags"))
   .settings(
     Compile / unmanagedSourceDirectories := Seq(),
     sharedSettings,
     mtagsSettings,
     Compile / unmanagedSourceDirectories += (ThisBuild / baseDirectory).value / "mtags" / "src" / "main" / "scala",
     Compile / unmanagedSourceDirectories += (ThisBuild / baseDirectory).value / "mtags-shared" / "src" / "main" / "scala",
-    Compile / unmanagedSourceDirectories += (ThisBuild / baseDirectory).value / "mtags-shared" / "src" / "main" / "scala-3",
-    moduleName := "mtags3",
-    scalaVersion := V.scala3,
-    target := (ThisBuild / baseDirectory).value / "mtags" / "target" / "target3",
+    Compile / unmanagedSourceDirectories += (ThisBuild / baseDirectory).value / "mtags-shared" / "src" / "main" / "scala-2.13",
+    moduleName := "mtags2",
+    scalaVersion := V.scala213,
+    target := (ThisBuild / baseDirectory).value / "mtags" / "target" / "target2",
     publish / skip := true,
     libraryDependencies += V.guava,
     scalafixConfig := Some(
-      (ThisBuild / baseDirectory).value / ".scalafix3.conf"
+      (ThisBuild / baseDirectory).value / ".scalafix2.conf"
     ),
   )
   .dependsOn(interfaces)
@@ -421,7 +440,8 @@ lazy val metals = project
       // for BSP
       "org.scala-sbt.ipcsocket" % "ipcsocket" % "1.6.2",
       "ch.epfl.scala" % "bsp4j" % V.bsp,
-      "ch.epfl.scala" %% "bloop-launcher-core" % V.bloop,
+      ("ch.epfl.scala" %% "bloop-launcher-core" % V.bloop)
+        .cross(CrossVersion.for3Use2_13),
       // for LSP
       V.lsp4j,
       // for DAP
@@ -451,14 +471,20 @@ lazy val metals = project
       // Scala dependencies
       // ==================
       "org.scalameta" % "mdoc-interfaces" % V.mdoc,
-      "org.scalameta" %% "scalafmt-dynamic" % V.scalafmt,
+      ("org.scalameta" %% "scalafmt-dynamic" % V.scalafmt)
+        .cross(CrossVersion.for3Use2_13),
+      "com.googlecode.java-diff-utils" % "diffutils" % "1.3.0",
       "ch.epfl.scala" % "scalafix-interfaces" % V.scalafix,
       // For reading classpaths.
       // for fetching ch.epfl.scala:bloop-frontend and other library dependencies
       "io.get-coursier" % "interface" % V.coursierInterfaces,
       // for comparing versions && fetching from sbt maven repository
-      "io.get-coursier" %% "coursier" % V.coursier,
-      "io.get-coursier" %% "coursier-sbt-maven-repository" % V.coursier,
+      ("io.get-coursier" %% "versions" % "0.3.2")
+        .cross(CrossVersion.for3Use2_13),
+      ("io.get-coursier" %% "coursier-sbt-maven-repository" % V.coursier)
+        .cross(CrossVersion.for3Use2_13),
+      ("io.get-coursier" %% "coursier" % V.coursier)
+        .cross(CrossVersion.for3Use2_13),
       // for logging
       "com.outr" %% "scribe" % V.scribe,
       "com.outr" %% "scribe-file" % V.scribe,
@@ -467,13 +493,11 @@ lazy val metals = project
       "com.lihaoyi" %% "ujson" % "3.3.1",
       // For fetching projects' templates
       "com.lihaoyi" %% "requests" % "0.8.2",
-      // for producing SemanticDB from Scala source files, to be sure we want the same version of scalameta
-      "org.scalameta" %% "scalameta" % V.semanticdb(scalaVersion.value),
-      "org.scalameta" % "semanticdb-scalac-core" % V.semanticdb(
-        scalaVersion.value
-      ) cross CrossVersion.full,
+      // for producing SemanticDB from Scala source files
+      scalametaDependency,
       // For starting Ammonite
-      "io.github.alexarchambault.ammonite" %% "ammonite-runner" % "0.4.0",
+      ("io.github.alexarchambault.ammonite" %% "ammonite-runner" % "0.4.0")
+        .cross(CrossVersion.for3Use2_13),
       "org.scala-lang.modules" %% "scala-xml" % "2.3.0",
       "org.scala-lang.modules" %% "scala-parallel-collections" % "1.0.4",
       ("org.virtuslab.scala-cli" % "scala-cli-bsp" % V.scalaCli)
@@ -543,6 +567,7 @@ lazy val input = project
   .in(file("tests/input"))
   .settings(
     sharedSettings,
+    scalaVersion := V.scala213,
     scalacOptions -= "-Xsource:3",
     publish / skip := true,
     libraryDependencies ++= List(
@@ -719,6 +744,7 @@ lazy val metalsDependencies = project
   .in(file("target/.dependencies"))
   .settings(
     publish / skip := true,
+    scalaVersion := V.scala213,
     // silent the intransitive dependency warning
     publishMavenStyle := false,
     libraryDependencies ++= List(
@@ -749,8 +775,10 @@ lazy val unit = project
     sharedSettings,
     Test / javaOptions += "-Xmx2G",
     libraryDependencies ++= List(
-      "io.get-coursier" %% "coursier" % V.coursier, // for jars
-      "ch.epfl.scala" %% "bloop-config" % V.bloopConfig,
+      ("io.get-coursier" %% "coursier" % V.coursier)
+        .cross(CrossVersion.for3Use2_13), // for jars
+      ("ch.epfl.scala" %% "bloop-config" % V.bloopConfig)
+        .cross(CrossVersion.for3Use2_13),
       "org.scalameta" %% "munit" % V.munit,
     ),
     buildInfoPackage := "tests",

metals-bench/src/main/scala/bench/MetalsBench.scala

@@ -1,11 +1,6 @@
 package bench
 
-import scala.reflect.internal.util.BatchSourceFile
-import scala.reflect.io.VirtualFile
-import scala.tools.nsc.interactive.Global
-
 import scala.meta.dialects
-import scala.meta.interactive.InteractiveSemanticdb
 import scala.meta.internal.metals.EmptyReportContext
 import scala.meta.internal.metals.IdentifierIndex
 import scala.meta.internal.metals.JdkSources
@@ -22,7 +17,6 @@ import scala.meta.internal.mtags.SemanticdbClasspath
 import scala.meta.internal.parsing.Trees
 import scala.meta.internal.semanticdb.TextDocument
 import scala.meta.internal.tokenizers.LegacyScanner
-import scala.meta.internal.tokenizers.LegacyToken
 import scala.meta.io.AbsolutePath
 import scala.meta.io.Classpath
 
@@ -128,22 +122,6 @@ class MetalsBench {
     }
   }
 
-  @Benchmark
-  @BenchmarkMode(Array(Mode.SingleShotTime))
-  def scalacTokenize(): Unit = {
-    val g = global
-    scalaDependencySources.foreach { input =>
-      val unit = new g.CompilationUnit(
-        new BatchSourceFile(new VirtualFile(input.path), input.chars)
-      )
-      val scanner = g.newUnitScanner(unit)
-      scanner.init()
-      while (scanner.token != LegacyToken.EOF) {
-        scanner.nextToken()
-      }
-    }
-  }
-
   @Benchmark
   @BenchmarkMode(Array(Mode.SingleShotTime))
   def scalametaParse(): Unit = {
@@ -153,27 +131,6 @@ class MetalsBench {
     }
   }
 
-  lazy val global: Global = InteractiveSemanticdb.newCompiler()
-
-  @Benchmark
-  @BenchmarkMode(Array(Mode.SingleShotTime))
-  def scalacParse(): Unit = {
-    val g = global
-    scalaDependencySources.foreach { input =>
-      val unit = new g.CompilationUnit(
-        new BatchSourceFile(new VirtualFile(input.path), input.chars)
-      )
-      val tree = g.newUnitParser(unit).parse()
-      var i = 0
-      new g.Traverser {
-        override def apply[T <: g.Tree](tree: T): T = {
-          i += 1
-          super.apply(tree)
-        }
-      }.traverse(tree)
-    }
-  }
-
   @Benchmark
   @BenchmarkMode(Array(Mode.SingleShotTime))
   def mtagsJavaParse(): Unit = {

metals/src/main/scala/scala/meta/internal/bsp/BspConfigGenerator.scala

@@ -12,9 +12,9 @@ import scala.meta.internal.builds.BuildServerProvider
 import scala.meta.internal.builds.ShellRunner
 import scala.meta.internal.metals.Directories
 import scala.meta.internal.metals.Messages.BspProvider
-import scala.meta.internal.metals.MetalsEnrichments._
-import scala.meta.internal.metals.StatusBar
 import scala.meta.internal.metals.UserConfiguration
+import scala.meta.internal.metals.StatusBar
+import scala.meta.internal.metals.MetalsEnrichments.given
 import scala.meta.internal.metals.clients.language.MetalsLanguageClient
 import scala.meta.io.AbsolutePath
 
@@ -75,7 +75,7 @@ final class BspConfigGenerator(
       buildTools: List[BuildServerProvider]
   ): Future[(BuildServerProvider, BspConfigGenerationStatus)] = {
     for {
-      Some(buildTool) <- chooseBuildServerProvider(buildTools)
+      case Some(buildTool) <- chooseBuildServerProvider(buildTools)
       status <- buildTool.generateBspConfig(
         workspace,
         args => runUnconditionally(buildTool, args),