Stop interpreter from interpreting twice on enter

4 files changed, 39 insertions, 5 deletions

diff --git a/src/dotty/tools/dotc/repl/AmmoniteReader.scala b/src/dotty/tools/dotc/repl/AmmoniteReader.scala
index a3b2a1c56..0a49b8ea3 100644
--- a/src/dotty/tools/dotc/repl/AmmoniteReader.scala
+++ b/src/dotty/tools/dotc/repl/AmmoniteReader.scala
@@ -15,9 +15,9 @@ class AmmoniteReader(val interpreter: Interpreter)(implicit ctx: Context) extend
   val interactive = true
 
   def incompleteInput(str: String): Boolean =
-    interpreter.beQuietDuring(interpreter.interpret(str)) match {
+    interpreter.delayOutputDuring(interpreter.interpret(str)) match {
       case Interpreter.Incomplete => true
-      case _ => false // TODO: should perhaps save output here?
+      case _ => false
     }
 
   val reader = new java.io.InputStreamReader(System.in)
diff --git a/src/dotty/tools/dotc/repl/CompilingInterpreter.scala b/src/dotty/tools/dotc/repl/CompilingInterpreter.scala
index cfcce106e..d322aa404 100644
--- a/src/dotty/tools/dotc/repl/CompilingInterpreter.scala
+++ b/src/dotty/tools/dotc/repl/CompilingInterpreter.scala
@@ -78,6 +78,27 @@ class CompilingInterpreter(out: PrintWriter, ictx: Context) extends Compiler wit
 
   /** whether to print out result lines */
   private var printResults: Boolean = true
+  private var delayOutput: Boolean = false
+
+  var previousOutput: String = null
+
+  override def lastOutput() =
+    if (previousOutput == null) None
+    else {
+      val ret = Some(previousOutput)
+      previousOutput = null
+      ret
+    }
+
+  override def delayOutputDuring[T](operation: => T): T = {
+    val old = delayOutput
+    try {
+      delayOutput = true
+      operation
+    } finally {
+      delayOutput = old
+    }
+  }
 
   /** Temporarily be quiet */
   override def beQuietDuring[T](operation: => T): T = {
@@ -188,7 +209,9 @@ class CompilingInterpreter(out: PrintWriter, ictx: Context) extends Compiler wit
           Interpreter.Error // an error happened during compilation, e.g. a type error
         else {
           val (interpreterResultString, succeeded) = req.loadAndRun()
-          if (printResults || !succeeded)
+          if (delayOutput)
+            previousOutput = clean(interpreterResultString)
+          else if (printResults || !succeeded)
             out.print(clean(interpreterResultString))
           if (succeeded) {
             prevRequests += req
diff --git a/src/dotty/tools/dotc/repl/Interpreter.scala b/src/dotty/tools/dotc/repl/Interpreter.scala
index ea587a097..590baae0d 100644
--- a/src/dotty/tools/dotc/repl/Interpreter.scala
+++ b/src/dotty/tools/dotc/repl/Interpreter.scala
@@ -33,4 +33,10 @@ trait Interpreter {
 
   /** Suppress output during evaluation of `operation`. */
   def beQuietDuring[T](operation: => T): T
+
+  /** Suppresses output and saves it for `lastOutput` to collect */
+  def delayOutputDuring[T](operation: => T): T
+
+  /** Gets the last output not printed immediately */
+  def lastOutput(): Option[String]
 }
diff --git a/src/dotty/tools/dotc/repl/InterpreterLoop.scala b/src/dotty/tools/dotc/repl/InterpreterLoop.scala
index 64414fec3..53fd09c07 100644
--- a/src/dotty/tools/dotc/repl/InterpreterLoop.scala
+++ b/src/dotty/tools/dotc/repl/InterpreterLoop.scala
@@ -18,7 +18,7 @@ import scala.concurrent.ExecutionContext.Implicits.global
  *  After instantiation, clients should call the `run` method.
  *
  *  @author Moez A. Abdel-Gawad
- *  @author  Lex Spoon
+ *  @author Lex Spoon
  *  @author Martin Odersky
  */
 class InterpreterLoop(compiler: Compiler, config: REPL.Config)(implicit ctx: Context) {
@@ -167,7 +167,12 @@ class InterpreterLoop(compiler: Compiler, config: REPL.Config)(implicit ctx: Con
     else if (line startsWith ":")
       output.println("Unknown command.  Type :help for help.")
     else
-      shouldReplay = interpretStartingWith(line)
+      shouldReplay = interpreter.lastOutput() match { // don't interpret twice
+        case Some(oldRes) =>
+          output.print(oldRes)
+          Some(line)
+        case _ => interpretStartingWith(line)
+      }
 
     (true, shouldReplay)
   }