REPL: make truncation by characters configurable

via `-Vrepl-max-print-characters`
The default character limit changes: instead of cutting at 1000 chars,
it is now 50k. The previous default was rather low, and only
made sense because it was also (and confusingly) used for the
`MaxElements` truncation.

This compliments #16011 and is
based on our discussion there, specifically #16011 (review)

Author: mpollmeier

compiler/src/dotty/tools/dotc/config/ScalaSettings.scala

@@ -150,6 +150,7 @@ private sealed trait VerboseSettings:
   val VprofileSortedBy = ChoiceSetting("-Vprofile-sorted-by", "key", "Show metrics about sources and internal representations sorted by given column name", List("name", "path", "lines", "tokens", "tasty", "complexity"), "")
   val VprofileDetails = IntSetting("-Vprofile-details", "Show metrics about sources and internal representations of the most complex methods", 0)
   val VreplMaxPrintElements: Setting[Int] = IntSetting("-Vrepl-max-print-elements", "Number of elements to be printed before output is truncated.", 1000)
+  val VreplMaxPrintCharacters: Setting[Int] = IntSetting("-Vrepl-max-print-characters", "Number of characters to be printed before output is truncated.", 50000)
 
 /** -W "Warnings" settings
  */

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

@@ -28,8 +28,6 @@ private[repl] class Rendering(parentClassLoader: Option[ClassLoader] = None):
 
   import Rendering._
 
-  private val MaxStringElements: Int = 1000  // no need to mkString billions of elements
-
   private var myClassLoader: AbstractFileClassLoader = _
 
   /** (value, maxElements) => String */
@@ -89,16 +87,13 @@ private[repl] class Rendering(parentClassLoader: Option[ClassLoader] = None):
       myClassLoader
     }
 
-  /** Used to elide long output in replStringOf.
-   *
-   * TODO: Perhaps implement setting scala.repl.maxprintstring as in Scala 2, but
-   * then this bug will surface, so perhaps better not?
-   * https://github.com/scala/bug/issues/12337
-   */
-  private[repl] def truncate(str: String): String =
+  /** Used to elide long output in replStringOf via `-Vrepl-max-print-characters` */
+  private[repl] def truncate(str: String)(using ctx: Context): String =
+    val maxPrintCharacters = ctx.settings.VreplMaxPrintCharacters.valueIn(ctx.settingsState)
+    val showTruncated = " ... large output truncated, print value to show all"
     val ncp = str.codePointCount(0, str.length) // to not cut inside code point
-    if ncp <= MaxStringElements then str
-    else str.substring(0, str.offsetByCodePoints(0, MaxStringElements - 1)) + infoOutputGotTruncated
+    if ncp <= maxPrintCharacters then str
+    else str.substring(0, str.offsetByCodePoints(0, maxPrintCharacters - 1)) + showTruncated
 
   /** Return a String representation of a value we got from `classLoader()`. */
   private[repl] def replStringOf(value: Object)(using Context): String =

compiler/test-resources/repl/i11377

@@ -0,0 +1,7 @@
+scala> 1.to(10).mkString
+val res0: String = 12345678910
+
+scala>:settings -Vrepl-max-print-characters:10
+
+scala> 1.to(10).mkString
+val res1: String = 123456789 ... large output truncated, print value to show all