Handle multi-command with reload correctly

@olegych reported that sbt would silently swallow the 'compile' command
in the multi-command, 'run;compile;reload'. I tracked this down to the
build source check. When the build has
Global / onChangedBuildSource := ReloadOnSourceChanges, the check build
sources command return a new state with "reload" prefixed. To actually
perform the reload, I returned this modified state with the prefixed
reload command.

There were two problems with this:
1) In the auto-reload case, the current command was not run after the
   reload
2) If the multi-command contained reload, the auto-reload check would
   have a false positive which triggered the bug in (1)

To fix this, I clear out the remaining commands before I run the check
command. That way, we know that if the remaining commands has a reload,
then it is an auto-reload. We then prefix the state with both the reload
and the current command.

I updated the scripted test for auto-reload to handle multi commands
containing reload.

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

@@ -214,12 +214,12 @@ object MainLoop {
       }
       Parser.parse(
         checkCommand,
-        state.put(Aggregation.suppressShow, true).combinedParser
+        state.copy(remainingCommands = Nil).put(Aggregation.suppressShow, true).combinedParser
       ) match {
         case Right(cmd) =>
           cmd() match {
             case s if s.remainingCommands.headOption.map(_.commandLine).contains("reload") =>
-              s.remove(Aggregation.suppressShow)
+              Exec("reload", None, None) +: exec +: state
             case _ => process()
           }
         case Left(_) => process()

sbt/src/sbt-test/nio/reload/build.sbt

@@ -1,4 +1,13 @@
-val foo = taskKey[Unit]("working task")
-foo := { println("foo") }
+val foo = inputKey[Unit]("working task")
+foo := {
+  val filename = Def.spaceDelimited("").parsed.head
+  IO.touch(baseDirectory.value / filename)
+}
+
+val exists = inputKey[Unit]("check that the file was written")
+exists := {
+  val filename = Def.spaceDelimited("").parsed.head
+  assert((baseDirectory.value / filename).exists)
+}
 
 Global / onChangedBuildSource := ReloadOnSourceChanges

sbt/src/sbt-test/nio/reload/changes/broken.sbt

@@ -1,4 +1,10 @@
-val foo = taskKey[Unit]("broken task")
+val foo = inputKey[Unit]("broken task")
 foo := { throw new IllegalStateException("foo") }
 
+val exists = inputKey[Unit]("check that the file was written")
+exists := {
+  val filename = Def.spaceDelimited("").parsed.head
+  assert((baseDirectory.value / filename).exists)
+}
+
 Global / onChangedBuildSource := ReloadOnSourceChanges

sbt/src/sbt-test/nio/reload/changes/working.sbt

@@ -1,4 +1,13 @@
-val foo = taskKey[Unit]("working task")
-foo := { println("foo") }
+val foo = inputKey[Unit]("working task")
+foo := {
+  val filename = Def.spaceDelimited("").parsed.head
+  IO.touch(baseDirectory.value / filename)
+}
+
+val exists = inputKey[Unit]("check that the file was written")
+exists := {
+  val filename = Def.spaceDelimited("").parsed.head
+  assert((baseDirectory.value / filename).exists)
+}
 
 Global / onChangedBuildSource := ReloadOnSourceChanges

sbt/src/sbt-test/nio/reload/test

@@ -1,9 +1,19 @@
-> foo
+> foo bar
+
+> exists bar
 
 $ copy-file changes/broken.sbt build.sbt
 
--> foo
+-> foo baz
+
+-> exists baz
 
 $ copy-file changes/working.sbt build.sbt
 
-> foo
+> foo baz
+
+> exists baz
+
+> foo foo; reload
+
+> exists foo