bugfix: Forward standard output to logger

Causes VirtusLab/scala-cli#1023

backend/src/main/scala/bloop/logging/BloopLogger.scala

@@ -30,7 +30,7 @@ final class BloopLogger(
     originId: Option[String]
 ) extends Logger {
 
-  redirectOutputToLogs(out)
+  redirectOutputToLogs(System.out)
 
   override def ansiCodesSupported() = true
   override def debug(msg: String)(implicit ctx: DebugFilter): Unit =

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

@@ -1,13 +1,15 @@
 // scalafmt: { maxColumn = 250 }
 package sbt.internal.inc.bloop.internal
 
+import java.io.ByteArrayOutputStream
 import java.nio.file.Files
 import java.util.Optional
 
 import scala.concurrent.Promise
 import scala.util.control.NonFatal
 
 import bloop.logging.ObservedLogger
+import bloop.logging.TeeOutputStream
 import bloop.reporter.ZincReporter
 import bloop.task.Task
 import bloop.tracing.BraveTracer
@@ -107,6 +109,14 @@ final class BloopHighLevelCompiler(
           }
         }
 
+        def withTee(block: TeeOutputStream => Unit) = {
+          System.out match {
+            case tee: TeeOutputStream =>
+              block(tee)
+            case _ =>
+          }
+
+        }
         def compileSources(
             sources: Seq[VirtualFile],
             scalacOptions: Array[String],
@@ -120,6 +130,11 @@ final class BloopHighLevelCompiler(
             throw new CompileFailed(new Array(0), s"Expected Scala library jar in Scala instance containing ${scalac.scalaInstance.allJars().mkString(", ")}", new Array(0))
           }
           try {
+            val baos = new ByteArrayOutputStream()
+            withTee {
+              _.addListener(baos)
+            }
+
             scalac.compile(
               sources.toArray,
               classpath.toArray,
@@ -132,6 +147,13 @@ final class BloopHighLevelCompiler(
               config.progress.toOptional,
               logger
             )
+
+            withTee { tee =>
+              val result = baos.toString()
+              if (result.nonEmpty)
+                logger.info(baos.toString)
+              tee.removeListener(baos)
+            }
           } catch {
             case t: StackOverflowError =>
               val msg = "Encountered a StackOverflowError coming from the compiler. You might need to restart your Bloop build server"

backend/src/test/scala/bloop/logging/RecordingLogger.scala

@@ -16,6 +16,7 @@ class RecordingLogger(
   private[this] val messages = new ConcurrentLinkedQueue[(String, String)]
 
   redirectOutputToLogs(System.out)
+
   def clear(): Unit = messages.clear()
 
   def debugs: List[String] = getMessagesAt(Some("debug"))

shared/src/main/scala/bloop/logging/Logger.scala

@@ -1,6 +1,5 @@
 package bloop.logging
 
-import java.io.ByteArrayOutputStream
 import java.io.PrintStream
 import java.util.function.Supplier
 
@@ -10,9 +9,7 @@ abstract class Logger extends xsbti.Logger with BaseSbtLogger {
 
   // Duplicate the standard output so that we get printlns from the compiler
   protected def redirectOutputToLogs(out: PrintStream) = {
-    val baos = new ByteArrayOutputStream()
-    val duplicating = new DuplicatingOutputStream(out, baos, this)
-    System.setOut(new PrintStream(duplicating));
+    System.setOut(new TeeOutputStream(out))
   }
 
   /** The name of the logger */

shared/src/main/scala/bloop/logging/TeeOutputStream.scala

@@ -0,0 +1,36 @@
+package bloop.logging
+
+import java.io.PrintStream
+import java.io.ByteArrayOutputStream
+import scala.collection.concurrent.TrieMap
+
+class TeeOutputStream(targetPS: PrintStream) extends PrintStream(targetPS) {
+
+  private val allStreams = TrieMap.empty[Int, ByteArrayOutputStream];
+
+  override def write(b: Int): Unit = {
+    allStreams.values.foreach(
+      _.write(b)
+    )
+    targetPS.write(b)
+  }
+
+  override def write(buf: Array[Byte], off: Int, len: Int): Unit = {
+    allStreams.values.foreach(
+      _.write(buf, off, len)
+    )
+    targetPS.write(buf, off, len)
+  }
+
+  override def flush(): Unit = {
+    targetPS.flush()
+  }
+
+  def addListener(baos: ByteArrayOutputStream): Unit = {
+    allStreams += baos.hashCode -> baos
+  }
+
+  def removeListener(baos: ByteArrayOutputStream): Unit = {
+    allStreams -= baos.hashCode
+  }
+}