Make the DelegatingReporter aware of -nowarn

The test case compiles a project without and with this
setting and checks that a warning is and isn't emitted
respectively.

It's a multi-project build; this bug didn't seem to turn
up in a single-project build.

compile/interface/src/main/scala/xsbt/Command.scala

@@ -23,4 +23,7 @@ object Command
 	
 	def getWarnFatal(settings: Settings): Boolean =
 		settings.Xwarnfatal.value
+
+	def getNoWarn(settings: Settings): Boolean =
+		settings.nowarn.value
 }

compile/interface/src/main/scala/xsbt/DelegatingReporter.scala

@@ -9,13 +9,13 @@ package xsbt
 private object DelegatingReporter
 {
 	def apply(settings: scala.tools.nsc.Settings, delegate: xsbti.Reporter): DelegatingReporter =
-		new DelegatingReporter(Command.getWarnFatal(settings), delegate)
+		new DelegatingReporter(Command.getWarnFatal(settings), Command.getNoWarn(settings), delegate)
 }
 
 // The following code is based on scala.tools.nsc.reporters.{AbstractReporter, ConsoleReporter}
 // Copyright 2002-2009 LAMP/EPFL
 // Original author: Martin Odersky
-private final class DelegatingReporter(warnFatal: Boolean, private[this] var delegate: xsbti.Reporter) extends scala.tools.nsc.reporters.Reporter
+private final class DelegatingReporter(warnFatal: Boolean, noWarn: Boolean, private[this] var delegate: xsbti.Reporter) extends scala.tools.nsc.reporters.Reporter
 {
 	import scala.tools.nsc.util.{FakePos,NoPosition,Position}
 
@@ -36,8 +36,11 @@ private final class DelegatingReporter(warnFatal: Boolean, private[this] var del
 	}
 	protected def info0(pos: Position, msg: String, rawSeverity: Severity, force: Boolean)
 	{
-		val severity = if(warnFatal && rawSeverity == WARNING) ERROR else rawSeverity
-		delegate.log(convert(pos), msg, convert(severity))
+		val skip = rawSeverity == WARNING && noWarn
+		if (!skip) {
+			val severity = if(warnFatal && rawSeverity == WARNING) ERROR else rawSeverity
+			delegate.log(convert(pos), msg, convert(severity))
+		}
 	}
 	def convert(posIn: Position): xsbti.Position =
 	{

sbt/src/sbt-test/reporter/nowarn/build.sbt

@@ -0,0 +1,24 @@
+lazy val sub1 = project
+
+lazy val sub2 = project
+
+val assertNoWarning = taskKey[Unit]("checks warning *is not* emitted")
+
+val assertWarning = taskKey[Unit]("checks warning *is* emitted")
+
+def check(expectation: Boolean) = Def.task[Unit] {
+  val lastLog: File = BuiltinCommands.lastLogFile(state.value).get
+  val last: String = IO.read(lastLog)
+  val contains = last.contains("a pure expression does nothing in statement position")
+  if (expectation && !contains)
+    sys.error("compiler output does not contain warning")
+  else if (!expectation && contains)
+    sys.error(s"compiler output still contains warning")
+  else {
+    IO.write(lastLog, "") // clear the backing log for for 'last'.
+  }
+}
+
+assertWarning <<= check(true)
+
+assertNoWarning <<= check(false)

sbt/src/sbt-test/reporter/nowarn/sub1/warney.scala

@@ -0,0 +1,6 @@
+object warney {
+	def foo = {
+    0
+  	0
+	}
+}

sbt/src/sbt-test/reporter/nowarn/sub2/sub2.scala

@@ -0,0 +1 @@
+object sub2

sbt/src/sbt-test/reporter/nowarn/test

@@ -0,0 +1,11 @@
+> compile
+
+> assertWarning
+
+> 'set every scalacOptions := Seq("-nowarn")'
+
+> clean
+
+> compile
+
+> assertNoWarning