Try get rid of CompletableFuture start using TaskApp

preliminary changes to get rid of CompletableFuture from Cli and use Deffered isntead and start using TaskApp instead of App

One compile test is failing, not sure if end conditions are ok. It would be good to add some tests

Author: Michał Wiącek

backend/src/main/scala/bloop/task/ObservableDeferred.scala

@@ -0,0 +1,39 @@
+package bloop.task
+
+import cats.effect.Concurrent
+import cats.effect.concurrent.{Deferred, Ref}
+import monix.eval.{Task => MonixTask}
+import monix.execution.atomic.AtomicBoolean
+
+class ObservableDeferred[A](
+    ref: Deferred[MonixTask, A],
+    state: Ref[MonixTask, Boolean],
+    syncFlag: AtomicBoolean
+) {
+  def complete(value: A): MonixTask[Unit] = {
+    MonixTask.defer {
+      ref
+        .complete(value)
+        .flatMap { _ =>
+          syncFlag.set(true)
+          state.set(true)
+        }
+    }.uncancelable
+  }
+
+  def isCompletedUnsafe: Boolean = syncFlag.get
+
+  def isCompleted: MonixTask[Boolean] = state.get
+
+  def get: MonixTask[A] = ref.get
+}
+
+object ObservableDeferred {
+
+  def apply[A](implicit F: Concurrent[MonixTask]): MonixTask[ObservableDeferred[A]] =
+    for {
+      ref <- Deferred[MonixTask, A]
+      state <- Ref[MonixTask].of(false)
+    } yield new ObservableDeferred(ref, state, AtomicBoolean(false))
+
+}

build.sbt

@@ -105,6 +105,7 @@ lazy val backend = project
       Dependencies.libraryManagement,
       Dependencies.sourcecode,
       Dependencies.monix,
+      Dependencies.monixTest,
       Dependencies.directoryWatcher,
       Dependencies.zt,
       Dependencies.brave,
@@ -156,6 +157,7 @@ lazy val frontend: Project = project
       Dependencies.jsoniterMacros % Provided,
       Dependencies.scalazCore,
       Dependencies.monix,
+      Dependencies.monixTest,
       Dependencies.caseApp,
       Dependencies.scalaDebugAdapter,
       Dependencies.bloopConfig,

frontend/src/main/scala/bloop/Bloop.scala

@@ -1,22 +1,14 @@
 package bloop
 
 import scala.annotation.tailrec
-
 import bloop.cli.CliOptions
 import bloop.cli.Commands
 import bloop.cli.ExitStatus
 import bloop.data.ClientInfo
 import bloop.data.WorkspaceSettings
-import bloop.engine.Build
-import bloop.engine.BuildLoader
-import bloop.engine.Exit
-import bloop.engine.Interpreter
-import bloop.engine.NoPool
-import bloop.engine.Run
-import bloop.engine.State
+import bloop.engine.{Build, BuildLoader, ExecutionContext, Exit, Interpreter, NoPool, Run, State}
 import bloop.io.AbsolutePath
 import bloop.logging.BloopLogger
-
 import _root_.bloop.task.Task
 import caseapp.CaseApp
 import caseapp.RemainingArgs
@@ -50,7 +42,7 @@ object Bloop extends CaseApp[CliOptions] {
       // Ignore the exit status here, all we want is the task to finish execution or fail.
       Cli.waitUntilEndOfWorld(options, state.pool, config, state.logger) {
         t.map(s => { State.stateCache.updateBuild(s.copy(status = ExitStatus.Ok)); s.status })
-      }
+      }(ExecutionContext.ioScheduler)
 
       // Recover the state if the previous task has been successful.
       State.stateCache