Add Dotty support

backend/src/main/scala/bloop/Compiler.scala

@@ -5,6 +5,7 @@ import xsbti.T2
 import java.util.Optional
 import java.io.File
 
+import bloop.internal.Ecosystem
 import bloop.io.{AbsolutePath, Paths}
 import bloop.logging.Logger
 import bloop.reporter.Reporter
@@ -75,7 +76,10 @@ object Compiler {
       val reporter = compileInputs.reporter
       val compilerCache = new FreshCompilerCache
       val cacheFile = compileInputs.baseDirectory.resolve("cache").toFile
-      val incOptions = IncOptions.create()
+      val incOptions = {
+        if (!compileInputs.scalaInstance.isDotty) IncOptions.create()
+        else Ecosystem.supportDotty(IncOptions.create())
+      }
       val progress = Optional.empty[CompileProgress]
       Setup.create(lookup, skip, cacheFile, compilerCache, incOptions, reporter, progress, empty)
     }

backend/src/main/scala/bloop/ScalaInstance.scala

@@ -20,7 +20,7 @@ class ScalaInstance(
 
   private def isJar(filename: String): Boolean = filename.endsWith(".jar")
   private def hasScalaCompilerName(filename: String): Boolean =
-    filename.startsWith("scala-compiler")
+    if (isDotty) filename.startsWith("dotty-compiler") else filename.startsWith("scala-compiler")
   private def hasScalaLibraryName(filename: String): Boolean =
     filename.startsWith("scala-library")
 
@@ -33,6 +33,10 @@ class ScalaInstance(
     isJar(filename) && !hasScalaCompilerName(filename) && !hasScalaLibraryName(filename)
   }
 
+  /** Is this `ScalaInstance` using Dotty? */
+  def isDotty: Boolean =
+    organization == "ch.epfl.lamp" && sbt.internal.inc.ScalaInstance.isDotty(version)
+
   /** Tells us what the real version of the classloaded scalac compiler in this instance is. */
   override def actualVersion(): String = {
     // TODO: Report when the `actualVersion` and the passed in version do not match.

backend/src/main/scala/bloop/internal/Ecosystem.scala

@@ -0,0 +1,45 @@
+package bloop.internal
+
+import java.io.File
+import java.util.Optional
+
+import xsbti.compile.{
+  ClassFileManager,
+  ClassFileManagerUtil,
+  DefaultExternalHooks,
+  IncOptions,
+  WrappedClassFileManager
+}
+
+object Ecosystem {
+  def supportDotty(incOptions: IncOptions): IncOptions = {
+    val tastyFileManager = new ClassFileManager {
+      private[this] val inherited = ClassFileManagerUtil.getDefaultClassFileManager(incOptions)
+
+      def delete(classes: Array[File]): Unit = {
+        val tastySuffixes = List(".tasty", ".hasTasty")
+        inherited.delete(classes flatMap { classFile =>
+          if (classFile.getPath endsWith ".class") {
+            val prefix = classFile.getAbsolutePath.stripSuffix(".class")
+            tastySuffixes.map(suffix => new File(prefix + suffix)).filter(_.exists)
+          } else Nil
+        })
+      }
+
+      def generated(classes: Array[File]): Unit = {}
+      def complete(success: Boolean): Unit = {}
+    }
+    val inheritedHooks = incOptions.externalHooks
+    val externalClassFileManager: Optional[ClassFileManager] = Option(
+      inheritedHooks.getExternalClassFileManager.orElse(null)) match {
+      case Some(prevManager) =>
+        Optional.of(WrappedClassFileManager.of(prevManager, Optional.of(tastyFileManager)))
+      case None =>
+        Optional.of(tastyFileManager)
+    }
+
+    val newExternalHooks =
+      new DefaultExternalHooks(inheritedHooks.getExternalLookup, externalClassFileManager)
+    incOptions.withExternalHooks(newExternalHooks)
+  }
+}

backend/src/main/scala/sbt/internal/inc/bloop/ZincInternals.scala

@@ -22,15 +22,19 @@ object ZincInternals {
     def compilerBridgeId(scalaVersion: String) = {
       // Defaults to bridge for 2.13 for Scala versions bigger than 2.13.x
       scalaVersion match {
+        case sc if (sc startsWith "0.") => "dotty-sbt-bridge"
         case sc if (sc startsWith "2.10.") => "compiler-bridge_2.10"
         case sc if (sc startsWith "2.11.") => "compiler-bridge_2.11"
         case sc if (sc startsWith "2.12.") => "compiler-bridge_2.12"
-        case _                             => "compiler-bridge_2.13"
+        case _ => "compiler-bridge_2.13"
       }
     }
 
+    val organization = if (scalaInstance.isDotty) scalaInstance.organization else "ch.epfl.scala"
     val bridgeId = compilerBridgeId(scalaInstance.version)
-    ModuleID("ch.epfl.scala", bridgeId, latestVersion).withConfigurations(CompileConf).sources()
+    val version = if (scalaInstance.isDotty) scalaInstance.version else latestVersion
+
+    ModuleID(organization, bridgeId, version).withConfigurations(CompileConf).sources()
   }
 
   /**

frontend/src/test/scala/bloop/tasks/CompilationTaskTest.scala

@@ -24,6 +24,7 @@ class CompilationTaskTest {
     val `B2.scala` = "package p1\ntrait B"
     val `C.scala` = "package p2\nimport p0.A\nimport p1.B\nobject C extends A with B"
     val `C2.scala` = "package p2\nimport p0.A\nobject C extends A"
+    val `Dotty.scala` = "package p0\nobject Foo { val x: String | Int = 1 }"
   }
 
   @Test
@@ -232,4 +233,16 @@ class CompilationTaskTest {
         assert(msgs.exists(m => m._1 == "warn" && m._2.contains(targetMsg)))
     }
   }
+
+  @Test
+  def compileWithDotty080RC1: Unit = {
+    val logger = new RecordingLogger()
+    val scalaInstance =
+      ScalaInstance.resolve("ch.epfl.lamp", "dotty-compiler_0.8", "0.8.0-RC1", logger)
+    val structures = Map(RootProject -> Map("Dotty.scala" -> ArtificialSources.`Dotty.scala`))
+    checkAfterCleanCompilation(structures, Map.empty, scalaInstance = scalaInstance) { state =>
+      val projects = state.build.projects
+      assert(projects.forall(p => hasPreviousResult(p, state)))
+    }
+  }
 }