SI-9350 Command option -Xreporter

Add a setting to take a custom Reporter.

Example of reporter that discounts deprecations for purposes of
(not) failing the build:

```
import scala.tools.nsc.Settings
import scala.tools.nsc.reporters.ConsoleReporter

import scala.reflect.internal.util._

class MyReporter(ss: Settings) extends ConsoleReporter(ss) {
  var deprecationCount = 0
  override def warning(pos: Position, msg: String): Unit = {
    if (msg contains "is deprecated") deprecationCount += 1
    super.warning(pos, msg)
  }
  override def hasWarnings: Boolean = count(WARNING) - deprecationCount > 0
  override def reset() = { deprecationCount = 0 ; super.reset() }
}
```

Invoked as:

```
$ scalac -toolcp . -Xreporter myrep.MyReporter -Xfatal-warnings -deprecation test.scala
test.scala:8: warning: class C in package tester is deprecated: Don't use me
  Console println s"${new C}"
                          ^
one warning found
```

where the reporter class is in the current directory, placed on the tool class path.

Also flush on early-reported errors.

5 files changed, 31 insertions, 18 deletions

diff --git a/src/compiler/scala/tools/nsc/Driver.scala b/src/compiler/scala/tools/nsc/Driver.scala
index 6befa76b3f..b30744c4df 100644
--- a/src/compiler/scala/tools/nsc/Driver.scala
+++ b/src/compiler/scala/tools/nsc/Driver.scala
@@ -1,7 +1,7 @@
 package scala
 package tools.nsc
 
-import scala.tools.nsc.reporters.ConsoleReporter
+import scala.tools.nsc.reporters.{ ConsoleReporter, Reporter }
 import Properties.{ versionMsg, residentPromptString }
 import scala.reflect.internal.util.FakePos
 
@@ -9,39 +9,43 @@ abstract class Driver {
 
   val prompt = residentPromptString
 
-  var reporter: ConsoleReporter = _
+  var reporter: Reporter = _
   protected var command: CompilerCommand = _
   protected var settings: Settings = _
 
+  /** Forward errors to the (current) reporter. */
   protected def scalacError(msg: String): Unit = {
     reporter.error(FakePos("scalac"), msg + "\n  scalac -help  gives more information")
   }
 
+  /** True to continue compilation. */
   protected def processSettingsHook(): Boolean = {
-    if (settings.version) { reporter echo versionMsg ; false } else true
+    if (settings.version) { reporter echo versionMsg ; false }
+    else !reporter.hasErrors
   }
 
   protected def newCompiler(): Global
 
-  protected def doCompile(compiler: Global) {
+  protected def doCompile(compiler: Global): Unit = {
     if (command.files.isEmpty) {
       reporter.echo(command.usageMsg)
       reporter.echo(compiler.pluginOptionsHelp)
     } else {
       val run = new compiler.Run()
       run compile command.files
-      reporter.printSummary()
+      reporter.finish()
     }
   }
 
-  def process(args: Array[String]) {
+  def process(args: Array[String]): Boolean = {
     val ss   = new Settings(scalacError)
-    reporter = new ConsoleReporter(ss)
+    reporter = new ConsoleReporter(ss)    // for reporting early config errors, before compiler is constructed
     command  = new CompilerCommand(args.toList, ss)
     settings = command.settings
 
     if (processSettingsHook()) {
       val compiler = newCompiler()
+      reporter     = compiler.reporter    // adopt the configured reporter
       try {
         if (reporter.hasErrors)
           reporter.flush()
@@ -57,11 +61,9 @@ abstract class Driver {
             case _                => throw ex // unexpected error, tell the outside world.
           }
       }
-    }
+    } else if (reporter.hasErrors) reporter.flush()
+    !reporter.hasErrors
   }
 
-  def main(args: Array[String]) {
-    process(args)
-    sys.exit(if (reporter.hasErrors) 1 else 0)
-  }
+  def main(args: Array[String]): Unit = sys.exit(if (process(args)) 0 else 1)
 }
diff --git a/src/compiler/scala/tools/nsc/Global.scala b/src/compiler/scala/tools/nsc/Global.scala
index 778f2fed59..965f984367 100644
--- a/src/compiler/scala/tools/nsc/Global.scala
+++ b/src/compiler/scala/tools/nsc/Global.scala
@@ -15,7 +15,7 @@ import io.{ SourceReader, AbstractFile, Path }
 import reporters.{ Reporter, ConsoleReporter }
 import util.{ ClassFileLookup, ClassPath, MergedClassPath, StatisticsInfo, returning }
 import scala.reflect.ClassTag
-import scala.reflect.internal.util.{ SourceFile, NoSourceFile, BatchSourceFile, ScriptSourceFile }
+import scala.reflect.internal.util.{ ScalaClassLoader, SourceFile, NoSourceFile, BatchSourceFile, ScriptSourceFile }
 import scala.reflect.internal.pickling.PickleBuffer
 import symtab.{ Flags, SymbolTable, SymbolTrackers }
 import symtab.classfile.Pickler
@@ -90,7 +90,7 @@ class Global(var currentSettings: Settings, var reporter: Reporter)
     this(new Settings(err => reporter.error(null, err)), reporter)
 
   def this(settings: Settings) =
-    this(settings, new ConsoleReporter(settings))
+    this(settings, Global.reporter(settings))
 
   def picklerPhase: Phase = if (currentRun.isDefined) currentRun.picklerPhase else NoPhase
 
@@ -1703,4 +1703,12 @@ class Global(var currentSettings: Settings, var reporter: Reporter)
 
 object Global {
   def apply(settings: Settings, reporter: Reporter): Global = new Global(settings, reporter)
+
+  def apply(settings: Settings): Global = new Global(settings, reporter(settings))
+
+  private def reporter(settings: Settings): Reporter = {
+    //val loader = ScalaClassLoader(getClass.getClassLoader)  // apply does not make delegate
+    val loader = new ClassLoader(getClass.getClassLoader) with ScalaClassLoader
+    loader.create[Reporter](settings.reporter.value, settings.errorFn)(settings)
+  }
 }
diff --git a/src/compiler/scala/tools/nsc/Main.scala b/src/compiler/scala/tools/nsc/Main.scala
index a66ee572a9..e2cf49907b 100644
--- a/src/compiler/scala/tools/nsc/Main.scala
+++ b/src/compiler/scala/tools/nsc/Main.scala
@@ -17,7 +17,8 @@ class MainClass extends Driver with EvalLoop {
     new compiler.Run() compile command.files
   }
 
-  override def newCompiler(): Global = Global(settings, reporter)
+  override def newCompiler(): Global = Global(settings)
+
   override def doCompile(compiler: Global) {
     if (settings.resident) resident(compiler)
     else super.doCompile(compiler)
diff --git a/src/compiler/scala/tools/nsc/reporters/ConsoleReporter.scala b/src/compiler/scala/tools/nsc/reporters/ConsoleReporter.scala
index 5bf611a7b0..4bf92fd1fb 100644
--- a/src/compiler/scala/tools/nsc/reporters/ConsoleReporter.scala
+++ b/src/compiler/scala/tools/nsc/reporters/ConsoleReporter.scala
@@ -11,8 +11,7 @@ import java.io.{ BufferedReader, IOException, PrintWriter }
 import scala.reflect.internal.util._
 import StringOps._
 
-/**
- * This class implements a Reporter that displays messages on a text console.
+/** This class implements a Reporter that displays messages on a text console.
  */
 class ConsoleReporter(val settings: Settings, reader: BufferedReader, writer: PrintWriter) extends AbstractReporter {
   def this(settings: Settings) = this(settings, Console.in, new PrintWriter(Console.err, true))
@@ -85,5 +84,7 @@ class ConsoleReporter(val settings: Settings, reader: BufferedReader, writer: Pr
     }
   }
 
-  override def flush() { writer.flush() }
+  override def flush() = writer.flush()
+
+  override def finish() = printSummary()
 }
diff --git a/src/compiler/scala/tools/nsc/settings/ScalaSettings.scala b/src/compiler/scala/tools/nsc/settings/ScalaSettings.scala
index c9d97a9469..c8251a542c 100644
--- a/src/compiler/scala/tools/nsc/settings/ScalaSettings.scala
+++ b/src/compiler/scala/tools/nsc/settings/ScalaSettings.scala
@@ -134,6 +134,7 @@ trait ScalaSettings extends AbsScalaSettings
   val Xshowobj           = StringSetting       ("-Xshow-object", "object", "Show internal representation of object.", "")
   val showPhases         = BooleanSetting      ("-Xshow-phases", "Print a synopsis of compiler phases.")
   val sourceReader       = StringSetting       ("-Xsource-reader", "classname", "Specify a custom method for reading source files.", "")
+  val reporter           = StringSetting       ("-Xreporter", "classname", "Specify a custom reporter for compiler messages.", "scala.tools.nsc.reporters.ConsoleReporter")
   val strictInference    = BooleanSetting      ("-Xstrict-inference", "Don't infer known-unsound types")
   val source             = ScalaVersionSetting ("-Xsource", "version", "Treat compiler input as Scala source for the specified version, see SI-8126.", initial = ScalaVersion("2.11"))