diff --git a/compiler/src/dotty/tools/repl/ReplDriver.scala b/compiler/src/dotty/tools/repl/ReplDriver.scala index b072d58f6bb7..905f4f06de08 100644 --- a/compiler/src/dotty/tools/repl/ReplDriver.scala +++ b/compiler/src/dotty/tools/repl/ReplDriver.scala @@ -187,19 +187,34 @@ class ReplDriver(settings: Array[String], // TODO: i5069 final def bind(name: String, value: Any)(using state: State): State = state + /** + * Controls whether the `System.out` and `System.err` streams are set to the provided constructor parameter instance + * of [[java.io.PrintStream]] during the execution of the repl. On by default. + * + * Disabling this can be beneficial when executing a repl instance inside a concurrent environment, for example a + * thread pool (such as the Scala compile server in the Scala Plugin for IntelliJ IDEA). + * + * In such environments, indepently executing `System.setOut` and `System.setErr` without any synchronization can + * lead to unpredictable results when restoring the original streams (dependent on the order of execution), leaving + * the Java process in an inconsistent state. + */ + protected def redirectOutput: Boolean = true + // redirecting the output allows us to test `println` in scripted tests private def withRedirectedOutput(op: => State): State = { - val savedOut = System.out - val savedErr = System.err - try { - System.setOut(out) - System.setErr(out) - op - } - finally { - System.setOut(savedOut) - System.setErr(savedErr) - } + if redirectOutput then + val savedOut = System.out + val savedErr = System.err + try { + System.setOut(out) + System.setErr(out) + op + } + finally { + System.setOut(savedOut) + System.setErr(savedErr) + } + else op } private def newRun(state: State, reporter: StoreReporter = newStoreReporter) = {