Introduce ReplPrinter as a hook for alternatives to replStringOf

src/repl/scala/tools/nsc/interpreter/IMain.scala

@@ -909,32 +909,63 @@ class IMain(initialSettings: Settings, protected val out: JPrintWriter) extends
     private[interpreter] lazy val ObjectSourceCode: Wrapper =
       if (isClassBased) new ClassBasedWrapper else new ObjectBasedWrapper
 
-    private object ResultObjectSourceCode extends IMain.CodeAssembler[MemberHandler] {
+    private lazy val ResultObjectSourceCode: ResultObjectSourceCode =
+      if (isClassBased) ClassBasedResultObjectSourceCode else ObjectBasedResultObjectSourceCode
+
+    private object ObjectBasedResultObjectSourceCode extends ResultObjectSourceCode {
+      def prewrap = importsPreamble
+      def postwrap = s"""
+      |  %s
+      |  lazy val %s: _root_.java.lang.String = %s {
+      |    %s
+      |  }
+      """.stripMargin.format(
+        importsTrailer, lineRep.printName, executionWrapper,
+        lineRep.evalPath + accessPath + "." + lineRep.printName
+      )
+    }
+
+    private object ClassBasedResultObjectSourceCode extends ResultObjectSourceCode {
+      def prewrap = ""
+      def postwrap = ""
+    }
+
+    private abstract class ResultObjectSourceCode extends IMain.CodeAssembler[MemberHandler] {
       /** We only want to generate this code when the result
        *  is a value which can be referred to as-is.
        */
       val evalResult = Request.this.value match {
         case NoSymbol => ""
         case sym      => "lazy val %s = %s".format(lineRep.resultName, originalPath(sym))
       }
+
+      /** Like preamble for an import wrapper. */
+      def prewrap: String
+
+      /** Like postamble for an import wrapper. */
+      def postwrap: String
+
       // first line evaluates object to make sure constructor is run
       // initial "" so later code can uniformly be: + etc
       val preamble = """
       |object %s {
       |  %s
+      |  %s
       |  lazy val %s: _root_.java.lang.String = %s {
       |    %s
       |    (""
       """.stripMargin.format(
-        lineRep.evalName, evalResult, lineRep.printName,
+        lineRep.evalName, evalResult, prewrap, lineRep.printName,
         executionWrapper, fullAccessPath
       )
 
       val postamble = """
       |    )
       |  }
+      |  %s
       |}
-      """.stripMargin
+      """.stripMargin.format(postwrap)
+
       val generate = (m: MemberHandler) => m resultExtractionCode Request.this
     }
 

src/repl/scala/tools/nsc/interpreter/ReplPrinter.scala

@@ -0,0 +1,14 @@
+package scala.tools.nsc
+package interpreter
+
+import scala.runtime.ScalaRunTime
+
+trait ReplPrinter[-A] extends Any {
+  def print(x: A, maxElements: Int): String
+}
+
+object ReplPrinter {
+  implicit def default[A]: ReplPrinter[A] = new ReplPrinter[A] {
+    def print(x: A, maxElements: Int) = ScalaRunTime.replStringOf(x, maxElements)
+  }
+}

src/repl/scala/tools/nsc/interpreter/ReplStrings.scala

@@ -34,7 +34,9 @@ trait ReplStrings {
     "\"" + string2code(str) + "\""
 
   def any2stringOf(x: Any, maxlen: Int) =
-    "_root_.scala.runtime.ScalaRunTime.replStringOf(%s, %s)".format(x, maxlen)
+    "_root_.scala.tools.nsc.interpreter.replStringOf(%s, %s)".format(x, maxlen)
+
+  def replStringOf[A](x: A, maxElements: Int)(implicit p: ReplPrinter[A]): String = p.print(x, maxElements)
 
   // no escaped or nested quotes
   private[this] val inquotes = """(['"])(.*?)\1""".r

test/files/run/repl-out-dir.check

@@ -11,13 +11,17 @@ repl-out-dir-run.obj
         $eval$.class
         $eval.class
     $line2
+        $eval$$iw$$iw$.class
+        $eval$$iw$.class
         $eval$.class
         $eval.class
         $read$$iw$$iw$.class
         $read$$iw$.class
         $read$.class
         $read.class
     $line3
+        $eval$$iw$$iw$.class
+        $eval$$iw$.class
         $eval$.class
         $eval.class
         $read$$iw$$iw$.class
@@ -27,13 +31,17 @@ repl-out-dir-run.obj
         $read$.class
         $read.class
     $line4
+        $eval$$iw$$iw$.class
+        $eval$$iw$.class
         $eval$.class
         $eval.class
         $read$$iw$$iw$.class
         $read$$iw$.class
         $read$.class
         $read.class
     $line5
+        $eval$$iw$$iw$.class
+        $eval$$iw$.class
         $eval$.class
         $eval.class
         $read$$iw$$iw$.class

test/files/run/repl-printer-classbased.check

@@ -0,0 +1,41 @@
+
+scala> :paste < EOF
+// Entering paste mode (EOF to finish)
+
+trait Show[-A] extends Any { def show(x: A): String }
+object Show {
+  implicit def shouty[Any]: Show[Any] =
+    new Show[Any] { def show(x: Any) = if (x == null) "" else x.toString + "!" }
+}
+EOF
+
+// Exiting paste mode, now interpreting.
+
+defined trait Show
+defined object Show
+
+scala> 
+
+scala> implicitly[Show[Int]] show 23
+res0: String = 23!
+
+scala> 
+
+scala> import scala.tools.nsc.interpreter.ReplPrinter
+import scala.tools.nsc.interpreter.ReplPrinter
+
+scala> implicit def showReplPrinter[A](implicit z: Show[A]): ReplPrinter[A] = new ReplPrinter[A] {
+  def print(x: A, maxElements: Int): String = {
+    val s = z show x
+    val nl = if (s contains "\n") "\n" else ""
+    nl + s + "\n"
+  }
+}
+showReplPrinter: [A](implicit z: Show[A])scala.tools.nsc.interpreter.ReplPrinter[A]
+
+scala> 
+
+scala> 23
+res1: Int = 23
+
+scala> :quit

test/files/run/repl-printer-classbased.scala

@@ -0,0 +1,29 @@
+object Test extends scala.tools.partest.ReplTest {
+  override def transformSettings(settings: scala.tools.nsc.Settings) = {
+    settings.Yreplclassbased.value = true
+    settings
+  }
+
+  def code = """
+:paste < EOF
+trait Show[-A] extends Any { def show(x: A): String }
+object Show {
+  implicit def shouty[Any]: Show[Any] =
+    new Show[Any] { def show(x: Any) = if (x == null) "" else x.toString + "!" }
+}
+EOF
+
+implicitly[Show[Int]] show 23
+
+import scala.tools.nsc.interpreter.ReplPrinter
+implicit def showReplPrinter[A](implicit z: Show[A]): ReplPrinter[A] = new ReplPrinter[A] {
+  def print(x: A, maxElements: Int): String = {
+    val s = z show x
+    val nl = if (s contains "\n") "\n" else ""
+    nl + s + "\n"
+  }
+}
+
+23
+"""
+}

test/files/run/repl-printer.check

@@ -0,0 +1,41 @@
+
+scala> :paste < EOF
+// Entering paste mode (EOF to finish)
+
+trait Show[-A] extends Any { def show(x: A): String }
+object Show {
+  implicit def shouty[Any]: Show[Any] =
+    new Show[Any] { def show(x: Any) = if (x == null) "" else x.toString + "!" }
+}
+EOF
+
+// Exiting paste mode, now interpreting.
+
+defined trait Show
+defined object Show
+
+scala> 
+
+scala> implicitly[Show[Int]] show 23
+res0: String = 23!
+
+scala> 
+
+scala> import scala.tools.nsc.interpreter.ReplPrinter
+import scala.tools.nsc.interpreter.ReplPrinter
+
+scala> implicit def showReplPrinter[A](implicit z: Show[A]): ReplPrinter[A] = new ReplPrinter[A] {
+  def print(x: A, maxElements: Int): String = {
+    val s = z show x
+    val nl = if (s contains "\n") "\n" else ""
+    nl + s + "\n"
+  }
+}
+showReplPrinter: [A](implicit z: Show[A])scala.tools.nsc.interpreter.ReplPrinter[A]
+
+scala> 
+
+scala> 23
+res1: Int = 23!
+
+scala> :quit

test/files/run/repl-printer.scala

@@ -0,0 +1,24 @@
+object Test extends scala.tools.partest.ReplTest {
+  def code = """
+:paste < EOF
+trait Show[-A] extends Any { def show(x: A): String }
+object Show {
+  implicit def shouty[Any]: Show[Any] =
+    new Show[Any] { def show(x: Any) = if (x == null) "" else x.toString + "!" }
+}
+EOF
+
+implicitly[Show[Int]] show 23
+
+import scala.tools.nsc.interpreter.ReplPrinter
+implicit def showReplPrinter[A](implicit z: Show[A]): ReplPrinter[A] = new ReplPrinter[A] {
+  def print(x: A, maxElements: Int): String = {
+    val s = z show x
+    val nl = if (s contains "\n") "\n" else ""
+    nl + s + "\n"
+  }
+}
+
+23
+"""
+}