Add --close-io-streams flag to sbt

When we start sbt with the thin client, we want to close the server io
streams after it loads so that the client exiting won't crash the
server. When we are running the server as part of the server tests, it
is nice to have the server output. By setting the --close-io-streams
flag when we launch the server in the client, we are able to achieve
both.

main-command/src/main/scala/sbt/BasicCommandStrings.scala

@@ -203,6 +203,7 @@ $AliasCommand name=
     "Provides an interactive prompt from which commands can be run on a server."
   def DashClient: String = "-client"
   def DashDashClient: String = "--client"
+  def CloseIOStreams: String = "--close-io-streams"
 
   def StashOnFailure: String = "sbtStashOnFailure"
   def PopOnFailure: String = "sbtPopOnFailure"

main-command/src/main/scala/sbt/BasicKeys.scala

@@ -114,6 +114,11 @@ object BasicKeys {
     "List of template resolver infos.",
     1000
   )
+  private[sbt] val closeIOStreams = AttributeKey[Boolean](
+    "close-io-streams",
+    "Toggles wheter or not to close system in, out and error when the server starts.",
+    1000
+  )
 }
 
 case class TemplateResolverInfo(module: ModuleID, implementationClass: String)

main-command/src/main/scala/sbt/internal/client/NetworkClient.scala

@@ -160,7 +160,7 @@ class NetworkClient(
       else Nil
 
     val args = color ++ superShell ++ arguments.sbtArguments
-    val cmd = arguments.sbtScript +: args
+    val cmd = arguments.sbtScript +: args :+ BasicCommandStrings.CloseIOStreams
     val process =
       new ProcessBuilder(cmd: _*)
         .directory(arguments.baseDirectory)

main/src/main/scala/sbt/Main.scala

@@ -68,11 +68,14 @@ private[sbt] object xMain {
             NetworkClient.run(configuration, args)
             Exit(0)
           } else {
-            val state = StandardMain.initialState(
-              configuration,
-              Seq(defaults, early),
-              runEarly(DefaultsCommand) :: runEarly(InitCommand) :: BootCommand :: Nil
-            )
+            val closeStreams = userCommands.exists(_ == BasicCommandStrings.CloseIOStreams)
+            val state = StandardMain
+              .initialState(
+                configuration,
+                Seq(defaults, early),
+                runEarly(DefaultsCommand) :: runEarly(InitCommand) :: BootCommand :: Nil
+              )
+              .put(BasicKeys.closeIOStreams, closeStreams)
             StandardMain.runManaged(state)
           }
         }
@@ -183,7 +186,8 @@ object StandardMain {
     sys.props.put("jna.nosys", "true")
 
     import BasicCommandStrings.isEarlyCommand
-    val userCommands = configuration.arguments.map(_.trim)
+    val userCommands =
+      configuration.arguments.map(_.trim).filterNot(_ == BasicCommandStrings.CloseIOStreams)
     val (earlyCommands, normalCommands) = (preCommands ++ userCommands).partition(isEarlyCommand)
     val commands = (earlyCommands ++ normalCommands).toList map { x =>
       Exec(x, None)

main/src/main/scala/sbt/internal/CommandExchange.scala

@@ -217,6 +217,7 @@ private[sbt] final class CommandExchange {
           server = None
           firstInstance.set(false)
       }
+      if (s.get(BasicKeys.closeIOStreams).getOrElse(false)) Terminal.close()
     }
     s
   }