SI-9206: REPL custom welcome message

Can be specified by `-Dscala.repl.welcome=Greeting` or in properties
file. It takes the same format arguments as the prompt, viz, version,
Java version and JVM name.

It can be disabled by `-Dscala.repl.welcome` with no text.

Author: som-snytt

src/compiler/scala/tools/nsc/Properties.scala

@@ -12,8 +12,17 @@ object Properties extends scala.util.PropertiesTrait {
   protected def pickJarBasedOn = classOf[Global]
 
   // settings based on jar properties, falling back to System prefixed by "scala."
+
+  // messages to display at startup or prompt, format string with string parameters
+  // Scala version, Java version, JVM name
   def residentPromptString = scalaPropOrElse("resident.prompt", "\nnsc> ")
   def shellPromptString    = scalaPropOrElse("shell.prompt", "%nscala> ")
+  def shellWelcomeString   = scalaPropOrElse("shell.welcome",
+    """Welcome to Scala %1$s (%3$s, Java %2$s).
+      |Type in expressions to have them evaluated.
+      |Type :help for more information.""".stripMargin
+  )
+
   // message to display at EOF (which by default ends with
   // a newline so as not to break the user's terminal)
   def shellInterruptedString = scalaPropOrElse("shell.interrupted", f":quit$lineSeparator")

src/library/scala/sys/BooleanProp.scala

@@ -50,6 +50,7 @@ object BooleanProp {
     def get: String = "" + value
     val clear, enable, disable, toggle = ()
     def option = if (isSet) Some(value) else None
+    //def or[T1 >: Boolean](alt: => T1): T1 = if (value) true else alt
 
     protected def zero = false
   }

src/library/scala/sys/Prop.scala

@@ -58,6 +58,10 @@ trait Prop[+T] {
    */
   def option: Option[T]
 
+  // Do not open until 2.12.
+  //** This value if the property is set, an alternative value otherwise. */
+  //def or[T1 >: T](alt: => T1): T1
+
   /** Removes the property from the underlying map.
    */
   def clear(): Unit

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

@@ -30,3 +30,6 @@ class Formatting(indent: Int) {
     }
   )
 }
+object Formatting {
+  def forPrompt(prompt: String) = new Formatting(prompt.lines.toList.last.length)
+}

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

@@ -56,13 +56,9 @@ class ILoop(in0: Option[BufferedReader], protected val out: JPrintWriter)
 
   private var globalFuture: Future[Boolean] = _
 
-  /** Print a welcome message */
-  def printWelcome() {
-    echo(s"""
-      |Welcome to Scala $versionString ($javaVmName, Java $javaVersion).
-      |Type in expressions to have them evaluated.
-      |Type :help for more information.""".trim.stripMargin
-    )
+  /** Print a welcome message! */
+  def printWelcome(): Unit = {
+    Option(replProps.welcome) filter (!_.isEmpty) foreach echo
     replinfo("[info] started at " + new java.util.Date)
   }
 
@@ -111,10 +107,6 @@ class ILoop(in0: Option[BufferedReader], protected val out: JPrintWriter)
   }
 
   class ILoopInterpreter extends IMain(settings, out) {
-    // the expanded prompt but without color escapes and without leading newline, for purposes of indenting
-    override lazy val formatting: Formatting = new Formatting(
-      (replProps.promptString format Properties.versionNumberString).lines.toList.last.length
-    )
     override protected def parentClassLoader =
       settings.explicitParentLoader.getOrElse( classOf[ILoop].getClassLoader )
   }

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

@@ -113,9 +113,7 @@ class IMain(@BeanProperty val factory: ScriptEngineFactory, initialSettings: Set
   def this() = this(new Settings())
 
   // the expanded prompt but without color escapes and without leading newline, for purposes of indenting
-  lazy val formatting: Formatting = new Formatting(
-    (replProps.promptString format Properties.versionNumberString).lines.toList.last.length
-  )
+  lazy val formatting = Formatting.forPrompt(replProps.promptText)
   lazy val reporter: ReplReporter = new ReplReporter(this)
 
   import formatting.indentCode

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

@@ -6,9 +6,11 @@
 package scala.tools.nsc
 package interpreter
 
-import Properties.shellPromptString
+import Properties.{ javaVersion, javaVmName, shellPromptString, shellWelcomeString,
+                    versionString, versionNumberString }
 import scala.sys._
 import Prop._
+import java.util.{ Formattable, FormattableFlags, Formatter }
 
 class ReplProps {
   private def bool(name: String) = BooleanProp.keyExists(name)
@@ -22,12 +24,37 @@ class ReplProps {
   val trace = bool("scala.repl.trace")
   val power = bool("scala.repl.power")
 
+  def enversion(s: String) = {
+    import FormattableFlags._
+    val v = new Formattable {
+      override def formatTo(formatter: Formatter, flags: Int, width: Int, precision: Int) = {
+        val version = if ((flags & ALTERNATE) != 0) versionNumberString else versionString
+        val left    = if ((flags & LEFT_JUSTIFY) != 0) "-" else ""
+        val w       = if (width >= 0) s"$width" else ""
+        val p       = if (precision >= 0) s".$precision" else ""
+        val fmt     = s"%${left}${w}${p}s"
+        formatter.format(fmt, version)
+      }
+    }
+    s.format(v, javaVersion, javaVmName)
+  }
+  def encolor(s: String)   = {
+    import scala.io.AnsiColor.{ MAGENTA, RESET }
+    if (colorOk) s"$MAGENTA$s$RESET" else s
+  }
+
   // Handy system prop for shell prompt, or else pick it up from compiler.properties
   val promptString = Prop[String]("scala.repl.prompt").option getOrElse (if (info) "%nscala %s> " else shellPromptString)
+  def promptText   = enversion(promptString)
   val prompt = {
     import scala.io.AnsiColor.{ MAGENTA, RESET }
-    val p = promptString format Properties.versionNumberString
-    if (colorOk) s"$MAGENTA$p$RESET" else p
+    if (colorOk) s"$MAGENTA$promptText$RESET" else promptText
+  }
+
+  //def welcome = enversion(Prop[String]("scala.repl.welcome") or shellWelcomeString)
+  def welcome = enversion {
+    val p = Prop[String]("scala.repl.welcome")
+    if (p.isSet) p.value else shellWelcomeString
   }
 
   /** CSV of paged,across to enable pagination or `-x` style