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.

1 files changed, 14 insertions, 12 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)
 }