Merge pull request sbt#3077 from eed3si9n/fport/3008

[fport] Notify & enable users to stay in the warm shell

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

@@ -196,14 +196,18 @@ object State {
 
   /** Provides operations and transformations on State. */
   implicit def stateOps(s: State): StateOps = new StateOps {
-    def process(f: (Exec, State) => State): State =
+    def process(f: (Exec, State) => State): State = {
+      def doX(x: Exec, xs: List[Exec]) = {
+        log.debug(s"> $x")
+        f(x, s.copy(remainingCommands = xs, currentCommand = Some(x), history = x :: s.history))
+      }
+      def isInteractive = System.console() != null
+      def hasInput = System.console().reader().ready()
       s.remainingCommands match {
-        case List() => exit(true)
-        case x :: xs =>
-          log.debug(s"> $x")
-          f(x, s.copy(remainingCommands = xs, currentCommand = Some(x), history = x :: s.history))
+        case List()           => if (isInteractive && hasInput) doX(Exec("shell", s.source), Nil) else exit(true)
+        case List(x, xs @ _*) => doX(x, xs.toList)
       }
-
+    }
     def :::(newCommands: List[String]): State = ++:(newCommands map { Exec(_, s.source) })
     def ++:(newCommands: List[Exec]): State = s.copy(remainingCommands = newCommands ::: s.remainingCommands)
     def ::(command: String): State = +:(Exec(command, s.source))

main/src/main/scala/sbt/MainLoop.scala

@@ -72,6 +72,19 @@ object MainLoop {
       val newLogging = state.globalLogging.newAppender(full, out, logBacking)
       // transferLevels(state, newLogging)
       val loggedState = state.copy(globalLogging = newLogging)
+      def isInteractive = System.console() != null
+      def hasCommand(cmd: String): Boolean =
+        (state.remainingCommands find { x => x.commandLine == cmd }).isDefined
+      /**
+       * The "boot" command adds "iflast shell" ("if last shell")
+       * which basically means it falls back to shell if there are no further commands
+       */
+      def endsWithBoot = state.remainingCommands.lastOption exists (_.commandLine == "boot")
+      if (isInteractive && !hasCommand("shell") && !hasCommand("server") && !endsWithBoot) {
+        state.log warn "Executing in batch mode."
+        state.log warn "  For better performance, hit [ENTER] to switch to interactive mode, or"
+        state.log warn "  consider launching sbt without any commands, or explicitly passing 'shell'"
+      }
       try run(loggedState) finally out.close()
     }
 

notes/0.13.14/stay-in-shell.md

@@ -0,0 +1,7 @@
+### Improvements
+
+- Notifies & enables users to stay in sbt's shell on the warm JVM by hitting \[ENTER\] while sbt is running. [#2987][]/[#2996][] by [@dwijnand][]
+
+[#2987]: https://github.com/sbt/sbt/issues/2987
+[#2996]: https://github.com/sbt/sbt/pull/2996
+[@dwijnand]: https://github.com/dwijnand