Add -Ywarn-unused & -Ywarn-unused-import, & fix warnings

internal/util-collection/src/main/scala/sbt/internal/util/Dag.scala

@@ -94,7 +94,6 @@ object Dag {
    */
   private[sbt] def findNegativeCycle[Node](graph: DirectedSignedGraph[Node]): List[graph.Arrow] =
     {
-      import scala.annotation.tailrec
       import graph._
       val finished = new mutable.HashSet[Node]
       val visited = new mutable.HashSet[Node]

internal/util-collection/src/main/scala/sbt/internal/util/INode.scala

@@ -3,7 +3,7 @@ package sbt.internal.util
 import java.lang.Runnable
 import java.util.concurrent.{ atomic, Executor, LinkedBlockingQueue }
 import atomic.{ AtomicBoolean, AtomicInteger }
-import Types.{ :+:, ConstK, Id }
+import Types.{ ConstK, Id }
 
 object EvaluationState extends Enumeration {
   val New, Blocked, Ready, Calling, Evaluated = Value

internal/util-collection/src/main/scala/sbt/internal/util/Param.scala

@@ -3,8 +3,6 @@
  */
 package sbt.internal.util
 
-import Types._
-
 // Used to emulate ~> literals
 trait Param[A[_], B[_]] {
   type T

internal/util-collection/src/main/scala/sbt/internal/util/Settings.scala

@@ -278,7 +278,6 @@ trait Init[Scope] {
 
   def flattenLocals(compiled: CompiledMap): Map[ScopedKey[_], Flattened] =
     {
-      import collection.breakOut
       val locals = compiled flatMap { case (key, comp) => if (key.key.isLocal) Seq[Compiled[_]](comp) else Nil }
       val ordered = Dag.topologicalSort(locals)(_.dependencies.flatMap(dep => if (dep.key.isLocal) Seq[Compiled[_]](compiled(dep)) else Nil))
       def flatten(cmap: Map[ScopedKey[_], Flattened], key: ScopedKey[_], deps: Iterable[ScopedKey[_]]): Flattened =
@@ -340,11 +339,6 @@ trait Init[Scope] {
         derivsByDef.getOrElseUpdate(key, new Deriveds(key, new mutable.ListBuffer)).settings += s
       }
 
-      // sort derived settings so that dependencies come first
-      // this is necessary when verifying that a derived setting's dependencies exist
-      val ddeps = (d: Deriveds) => d.dependencies.flatMap(derivsByDef.get)
-      val sortedDerivs = Dag.topologicalSort(derivsByDef.values)(ddeps)
-
       // index derived settings by triggering key.  This maps a key to the list of settings potentially derived from it.
       val derivedBy = new mutable.HashMap[AttributeKey[_], mutable.ListBuffer[Derived]]
       for (s <- derived; d <- s.triggeredBy)

internal/util-collection/src/test/scala/LiteralTest.scala

@@ -3,8 +3,6 @@
  */
 package sbt.internal.util
 
-import Types._
-
 // compilation test
 object LiteralTest {
   def x[A[_], B[_]](f: A ~> B) = f
@@ -14,4 +12,4 @@ object LiteralTest {
 
   val a: List[Int] = f(Some(3))
   val b: List[String] = f(Some("aa"))
-}
+}

internal/util-collection/src/test/scala/SettingsExample.scala

@@ -32,7 +32,6 @@ object SettingsExample extends Init[Scope] {
 
 object SettingsUsage {
   import SettingsExample._
-  import Types._
 
   // Define some keys
   val a = AttributeKey[Int]("a")

internal/util-complete/src/main/scala/sbt/internal/util/LineReader.scala

@@ -5,9 +5,8 @@ package sbt.internal.util
 
 import jline.console.ConsoleReader
 import jline.console.history.{ FileHistory, MemoryHistory }
-import java.io.{ File, InputStream, PrintWriter, FileInputStream, FileDescriptor, FilterInputStream }
+import java.io.{ File, InputStream, FileInputStream, FileDescriptor, FilterInputStream }
 import complete.Parser
-import java.util.concurrent.atomic.AtomicBoolean
 import scala.concurrent.duration.Duration
 import scala.annotation.tailrec
 

internal/util-complete/src/main/scala/sbt/internal/util/complete/EditDistance.scala

@@ -23,7 +23,6 @@ object EditDistance {
     for (i <- 1 to n; s_i = s(i - 1); j <- 1 to m) {
       val t_j = t(j - 1)
       val cost = if (s_i == t_j) matchCost else if (lower(s_i) == lower(t_j)) caseCost else subCost
-      val tcost = if (s_i == t_j) matchCost else transposeCost
 
       val c1 = d(i - 1)(j) + deleteCost
       val c2 = d(i)(j - 1) + insertCost
@@ -39,4 +38,4 @@ object EditDistance {
 
     d(n)(m)
   }
-}
+}

internal/util-complete/src/main/scala/sbt/internal/util/complete/HistoryCommands.scala

@@ -4,7 +4,6 @@
 package sbt.internal.util
 package complete
 
-import java.io.File
 import sbt.io.IO
 
 object HistoryCommands {

internal/util-complete/src/main/scala/sbt/internal/util/complete/JLineCompletion.scala

@@ -5,7 +5,7 @@ package sbt.internal.util
 package complete
 
 import jline.console.ConsoleReader
-import jline.console.completer.{ CandidateListCompletionHandler, Completer, CompletionHandler }
+import jline.console.completer.{ Completer, CompletionHandler }
 import scala.annotation.tailrec
 import collection.JavaConversions