Introduce option not to display definitions in repl driver

The reason for this change is that currently, statements in the
JSR223 script engine are evaluated twice. Once when the "run" method
is called, and once when the value of the result is extracted.
The first one needs not be, it exists solely due to displayDefinitions
being called. If we put it behind a flag, the problem is solved.

Author: rjolly

compiler/src/dotty/tools/repl/ReplDriver.scala

@@ -53,7 +53,8 @@ case class State(objectIndex: Int,
 /** Main REPL instance, orchestrating input, compilation and presentation */
 class ReplDriver(settings: Array[String],
                  out: PrintStream = Console.out,
-                 classLoader: Option[ClassLoader] = None) extends Driver {
+                 classLoader: Option[ClassLoader] = None,
+                 display: Boolean = true) extends Driver {
 
   /** Overridden to `false` in order to not have to give sources on the
    *  commandline
@@ -227,7 +228,10 @@ class ReplDriver(settings: Array[String],
 
             val warnings = newState.context.reporter.removeBufferedMessages(newState.context)
             displayErrors(warnings)(newState) // display warnings
-            displayDefinitions(unit.tpdTree, newestWrapper)(newStateWithImports)
+            if (display)
+              displayDefinitions(unit.tpdTree, newestWrapper)(newStateWithImports)
+            else
+              newStateWithImports
         }
       )
   }

compiler/src/dotty/tools/repl/ScriptEngine.scala

@@ -17,7 +17,7 @@ import dotc.core.StdNames.str
  *  println(e.eval("42"))
  */
 class ScriptEngine extends AbstractScriptEngine {
-  private[this] val driver = new ReplDriver(Array("-usejavacp", "-color:never"), Console.out, None)
+  private[this] val driver = new ReplDriver(Array("-usejavacp", "-color:never"), Console.out, None, false)
   private[this] val rendering = new Rendering
   private[this] var state: State = driver.initialState
 

sbt-bridge/src/xsbt/ConsoleInterface.java

@@ -40,7 +40,7 @@ public void run(
     completeArgsList.add(classpathString);
     String[] completeArgs = completeArgsList.toArray(args);
 
-    ReplDriver driver = new ReplDriver(completeArgs, System.out, Some.apply(loader));
+    ReplDriver driver = new ReplDriver(completeArgs, System.out, Some.apply(loader), true);
 
     State state = driver.initialState();
     assert bindNames.length == bindValues.length;