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/dotc/config/ScalaSettings.scala

@@ -75,6 +75,7 @@ class ScalaSettings extends Settings.SettingGroup {
   val XmainClass: Setting[String] = StringSetting("-Xmain-class", "path", "Class for manifest's Main-Class entry (only useful with -d <jar>)", "")
   val XnoValueClasses: Setting[Boolean] = BooleanSetting("-Xno-value-classes", "Do not use value classes. Helps debugging.")
   val XreplLineWidth: Setting[Int] = IntSetting("-Xrepl-line-width", "Maximal number of columns per line for REPL output", 390)
+  val XreplDisableDisplay: Setting[Boolean] = BooleanSetting("-Xrepl-disable-display", "Do not display definitions in REPL.")
   val XfatalWarnings: Setting[Boolean] = BooleanSetting("-Xfatal-warnings", "Fail the compilation if there are any warnings.")
   val XverifySignatures: Setting[Boolean] = BooleanSetting("-Xverify-signatures", "Verify generic signatures in generated bytecode.")
   val XignoreScala2Macros: Setting[Boolean] = BooleanSetting("-Xignore-scala2-macros", "Ignore errors when compiling code that calls Scala2 macros, these will fail at runtime.")

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

@@ -194,7 +194,9 @@ class ReplDriver(settings: Array[String],
       case _ => // new line, empty tree
         state
     }
-    out.println()
+    implicit val ctx: Context = newState.context
+    if (!ctx.settings.XreplDisableDisplay.value)
+      out.println()
     newState
   }
 
@@ -227,7 +229,11 @@ class ReplDriver(settings: Array[String],
 
             val warnings = newState.context.reporter.removeBufferedMessages(newState.context)
             displayErrors(warnings)(newState) // display warnings
-            displayDefinitions(unit.tpdTree, newestWrapper)(newStateWithImports)
+            implicit val ctx = newState.context
+            if (!ctx.settings.XreplDisableDisplay.value)
+              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", "-Xrepl-disable-display"), Console.out, None)
   private[this] val rendering = new Rendering
   private[this] var state: State = driver.initialState
 

tests/run-with-compiler/scripting.check

@@ -1,3 +1 @@
-val res0: Int = 42
-
 42

tests/run-with-compiler/scripting.scala

@@ -5,4 +5,3 @@ object Test {
     println(e.eval("42"))
   }
 }
-