refactor and make it work

backend/src/main/scala/bloop/ClientClassesObserver.scala

@@ -0,0 +1,65 @@
+package bloop
+
+import java.io.File
+import java.util.concurrent.atomic.AtomicReference
+
+import scala.jdk.CollectionConverters._
+
+import bloop.io.AbsolutePath
+import bloop.task.Task
+
+import monix.reactive.Observable
+import monix.reactive.subjects.PublishSubject
+import sbt.internal.inc.PlainVirtualFileConverter
+import xsbti.VirtualFileRef
+import xsbti.compile.CompileAnalysis
+import xsbti.compile.analysis.Stamp
+
+/**
+ * Each time a new compile analysis is produced for a given client, it is given to
+ * the [[ClientClassObserver]] which computes the list of classes that changed or got created.
+ *
+ * A client can subscribe to the observer to get notified of classes to update.
+ * It is used by DAP to hot reload classes in the debuggee process.
+ *
+ * @param clientClassesDir the class directory for the client
+ */
+private[bloop] class ClientClassesObserver(val classesDir: AbsolutePath) {
+  private val converter = PlainVirtualFileConverter.converter
+  private val previousAnalysis: AtomicReference[CompileAnalysis] = new AtomicReference()
+  private val classesSubject: PublishSubject[Seq[String]] = PublishSubject()
+
+  def observable: Observable[Seq[String]] = classesSubject
+
+  def nextAnalysis(analysis: CompileAnalysis): Task[Unit] = {
+    val prev = previousAnalysis.getAndSet(analysis)
+    if (prev != null && classesSubject.size > 0) {
+      Task {
+        val previousStamps = prev.readStamps.getAllProductStamps
+        analysis.readStamps.getAllProductStamps.asScala.iterator.collect {
+          case (vf, stamp) if isClassFile(vf) && isNewer(stamp, previousStamps.get(vf)) =>
+            getFullyQualifiedClassName(vf)
+        }.toSeq
+      }
+        .flatMap { classesToUpdate =>
+          Task.fromFuture(classesSubject.onNext(classesToUpdate)).map(_ => ())
+        }
+    } else Task.unit
+  }
+
+  private def isClassFile(vf: VirtualFileRef): Boolean = vf.id.endsWith(".class")
+
+  private def isNewer(current: Stamp, previous: Stamp): Boolean =
+    previous == null || {
+      val currentHash = current.getHash
+      val previousHash = previous.getHash
+      currentHash.isPresent &&
+      (!previousHash.isPresent || currentHash.get != previousHash.get)
+    }
+
+  private def getFullyQualifiedClassName(vf: VirtualFileRef): String = {
+    val path = converter.toPath(vf)
+    val relativePath = classesDir.underlying.relativize(path)
+    relativePath.toString.replace(File.separator, ".").stripSuffix(".class")
+  }
+}

backend/src/main/scala/bloop/CompileBackgroundTasks.scala

@@ -8,7 +8,7 @@ import bloop.tracing.BraveTracer
 
 abstract class CompileBackgroundTasks {
   def trigger(
-      clientClassesDir: AbsolutePath,
+      clientClassesObserver: ClientClassesObserver,
       clientReporter: Reporter,
       clientTracer: BraveTracer,
       clientLogger: Logger
@@ -20,7 +20,7 @@ object CompileBackgroundTasks {
   val empty: CompileBackgroundTasks = {
     new CompileBackgroundTasks {
       def trigger(
-          clientClassesDir: AbsolutePath,
+          clientClassesObserver: ClientClassesObserver,
           clientReporter: Reporter,
           clientTracer: BraveTracer,
           clientLogger: Logger

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

@@ -452,11 +452,12 @@ object Compiler {
 
             val backgroundTasks = new CompileBackgroundTasks {
               def trigger(
-                  clientClassesDir: AbsolutePath,
+                  clientClassesObserver: ClientClassesObserver,
                   clientReporter: Reporter,
                   clientTracer: BraveTracer,
                   clientLogger: Logger
               ): Task[Unit] = Task.defer {
+                val clientClassesDir = clientClassesObserver.classesDir
                 clientLogger.debug(s"Triggering background tasks for $clientClassesDir")
                 val updateClientState =
                   updateExternalClassesDirWithReadOnly(clientClassesDir, clientTracer, clientLogger)
@@ -472,10 +473,20 @@ object Compiler {
                 }
 
                 val deleteNewClassesDir = Task(BloopPaths.delete(AbsolutePath(newClassesDir)))
-                val allTasks = List(deleteNewClassesDir, updateClientState, writeAnalysisIfMissing)
+                val publishClientAnalysis = Task {
+                  rebaseAnalysisClassFiles(
+                    analysis,
+                    readOnlyClassesDir,
+                    clientClassesDir.underlying,
+                    sourcesWithFatal
+                  )
+                }
+                  .flatMap(clientClassesObserver.nextAnalysis)
                 Task
-                  .gatherUnordered(allTasks)
-                  .map(_ => ())
+                  .gatherUnordered(
+                    List(deleteNewClassesDir, updateClientState, writeAnalysisIfMissing)
+                  )
+                  .flatMap(_ => publishClientAnalysis)
                   .onErrorHandleWith(err => {
                     clientLogger.debug("Caught error in background tasks"); clientLogger.trace(err);
                     Task.raiseError(err)
@@ -495,14 +506,12 @@ object Compiler {
             )
           } else {
             val allGeneratedProducts = allGeneratedRelativeClassFilePaths.toMap
-            val analysisForFutureCompilationRuns = {
-              rebaseAnalysisClassFiles(
-                analysis,
-                readOnlyClassesDir,
-                newClassesDir,
-                sourcesWithFatal
-              )
-            }
+            val analysisForFutureCompilationRuns = rebaseAnalysisClassFiles(
+              analysis,
+              readOnlyClassesDir,
+              newClassesDir,
+              sourcesWithFatal
+            )
 
             val resultForFutureCompilationRuns = {
               resultForDependentCompilationsInSameRun.withAnalysis(
@@ -517,12 +526,12 @@ object Compiler {
             // Schedule the tasks to run concurrently after the compilation end
             val backgroundTasksExecution = new CompileBackgroundTasks {
               def trigger(
-                  clientClassesDir: AbsolutePath,
+                  clientClassesObserver: ClientClassesObserver,
                   clientReporter: Reporter,
                   clientTracer: BraveTracer,
                   clientLogger: Logger
               ): Task[Unit] = {
-                val clientClassesDirPath = clientClassesDir.toString
+                val clientClassesDir = clientClassesObserver.classesDir
                 val successBackgroundTasks =
                   backgroundTasksWhenNewSuccessfulAnalysis
                     .map(f => f(clientClassesDir, clientReporter, clientTracer))
@@ -543,15 +552,26 @@ object Compiler {
                       val syntax = path.syntax
                       if (syntax.startsWith(readOnlyClassesDirPath)) {
                         val rebasedFile = AbsolutePath(
-                          syntax.replace(readOnlyClassesDirPath, clientClassesDirPath)
+                          syntax.replace(readOnlyClassesDirPath, clientClassesDir.toString)
                         )
                         if (rebasedFile.exists) {
                           Files.delete(rebasedFile.underlying)
                         }
                       }
                     }
                   }
-                  Task.gatherUnordered(List(firstTask, secondTask)).map(_ => ())
+
+                  val publishClientAnalysis = Task {
+                    rebaseAnalysisClassFiles(
+                      analysis,
+                      newClassesDir,
+                      clientClassesDir.underlying,
+                      sourcesWithFatal
+                    )
+                  }.flatMap(clientClassesObserver.nextAnalysis)
+                  Task
+                    .gatherUnordered(List(firstTask, secondTask))
+                    .flatMap(_ => publishClientAnalysis)
                 }
 
                 allClientSyncTasks.doOnFinish(_ => Task(clientReporter.reportEndCompilation()))
@@ -691,11 +711,12 @@ object Compiler {
   ): CompileBackgroundTasks = {
     new CompileBackgroundTasks {
       def trigger(
-          clientClassesDir: AbsolutePath,
+          clientClassesObserver: ClientClassesObserver,
           clientReporter: Reporter,
           tracer: BraveTracer,
           clientLogger: Logger
       ): Task[Unit] = {
+        val clientClassesDir = clientClassesObserver.classesDir
         val backgroundTasks = tasks.map(f => f(clientClassesDir, clientReporter, tracer))
         Task.gatherUnordered(backgroundTasks).memoize.map(_ => ())
       }
@@ -783,19 +804,19 @@ object Compiler {
    */
   def rebaseAnalysisClassFiles(
       analysis0: CompileAnalysis,
-      readOnlyClassesDir: Path,
-      newClassesDir: Path,
+      origin: Path,
+      target: Path,
       sourceFilesWithFatalWarnings: scala.collection.Set[File]
   ): Analysis = {
     // Cast to the only internal analysis that we support
     val analysis = analysis0.asInstanceOf[Analysis]
     def rebase(file: VirtualFileRef): VirtualFileRef = {
 
       val filePath = converter.toPath(file).toAbsolutePath()
-      if (!filePath.startsWith(readOnlyClassesDir)) file
+      if (!filePath.startsWith(origin)) file
       else {
         // Hash for class file is the same because the copy duplicates metadata
-        val path = newClassesDir.resolve(readOnlyClassesDir.relativize(filePath))
+        val path = target.resolve(origin.relativize(filePath))
         converter.toVirtualFile(path)
       }
     }

frontend/src/main/scala/bloop/bsp/BloopBspServices.scala

@@ -603,10 +603,7 @@ final class BloopBspServices(
       params: bsp.DebugSessionParams
   ): BspEndpointResponse[bsp.DebugSessionAddress] = {
 
-    def inferDebuggee(
-        projects: Seq[Project],
-        state: State
-    ): BspResponse[Debuggee] = {
+    def inferDebuggee(projects: Seq[Project], state: State): BspResponse[Debuggee] = {
       def convert[A: JsonValueCodec](
           f: A => Either[String, Debuggee]
       ): Either[Response.Error, Debuggee] = {

frontend/src/main/scala/bloop/dap/BloopDebugToolsResolver.scala

@@ -34,13 +34,12 @@ class BloopDebugToolsResolver(logger: Logger) extends DebugToolsResolver {
     }
   }
 
-  override def resolveUnpickler(scalaVersion: ScalaVersion): Try[ClassLoader] = {
-    getOrTryUpdate(stepFilterCache, scalaVersion) {
-      val unpicklerModule = s"${BuildInfo.unpicklerName}_${scalaVersion.binaryVersion}"
-      val stepFilter = Artifact(BuildInfo.organization, unpicklerModule, BuildInfo.version)
-      val tastyCore = Artifact("org.scala-lang", "tasty-core_3", scalaVersion.value)
+  override def resolveDecoder(scalaVersion: ScalaVersion): Try[ClassLoader] = {
+    getOrTryUpdate(decoderCache, scalaVersion) {
+      val decoderModule = s"${BuildInfo.decoderName}_${scalaVersion.binaryVersion}"
+      val artifact = Artifact(BuildInfo.organization, decoderModule, BuildInfo.version)
       DependencyResolution
-        .resolveWithErrors(List(stepFilter, tastyCore), logger)
+        .resolveWithErrors(List(artifact), logger)
         .map(jars => toClassLoader(jars, true))
         .toTry
     }
@@ -66,5 +65,5 @@ class BloopDebugToolsResolver(logger: Logger) extends DebugToolsResolver {
 
 object BloopDebugToolsResolver {
   private val expressionCompilerCache: mutable.Map[ScalaVersion, ClassLoader] = mutable.Map.empty
-  private val stepFilterCache: mutable.Map[ScalaVersion, ClassLoader] = mutable.Map.empty
+  private val decoderCache: mutable.Map[ScalaVersion, ClassLoader] = mutable.Map.empty
 }