Rename early command to `early(command)`

Fixes #2734, Ref #1041
e93c4450a1 added a feature called early
command, which uses `--` as a prefix to denote some commands that runs
ahead of session loading. While the feature might be useful especially
for logging, `--` is too useful just for this purpose.

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

@@ -60,21 +60,18 @@ ${runEarly(level.toString)}
 		* if no other commands are passed, interactive mode is still entered
 """
 
-  def runEarly(command: String) = {
-    val sep = if (command.isEmpty || Character.isLetter(command.charAt(0))) "" else " "
-    s"$EarlyCommand$sep$command"
-  }
+  def runEarly(command: String) = s"$EarlyCommand($command)"
   private[sbt] def isEarlyCommand(s: String): Boolean = {
-    s.startsWith(EarlyCommand) && s != Compat.FailureWall && s != Compat.ClearOnFailure
+    s.startsWith(EarlyCommand + "(") && s.endsWith(")")
   }
 
-  val EarlyCommand = "--"
-  val EarlyCommandBrief = (s"$EarlyCommand<command>", "Schedules a command to run before other commands on startup.")
+  val EarlyCommand = "early"
+  val EarlyCommandBrief = (s"$EarlyCommand(<command>)", "Schedules a command to run before other commands on startup.")
   val EarlyCommandDetailed =
-    s"""$EarlyCommand<command>
+    s"""$EarlyCommand(<command>)
 
 	Schedules an early command, which will be run before other commands on the command line.
-	The order is preserved between all early commands, so `sbt --a --b` executes `a` and `b` in order.
+	The order is preserved between all early commands, so `sbt "early(a)" "early(b)"` executes `a` and `b` in order.
 """
 
   def ReadCommand = "<"

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

@@ -24,7 +24,10 @@ object BasicCommands {
   def ignore = Command.command(FailureWall)(idFun)
 
   def early = Command.arb(earlyParser, earlyHelp) { (s, other) => other :: s }
-  private[this] def earlyParser = (s: State) => token(EarlyCommand).flatMap(_ => otherCommandParser(s))
+  private[this] def earlyParser = (s: State) =>
+    token(EarlyCommand + "(") flatMap { _ =>
+      otherCommandParser(s) <~ token(")")
+    }
   private[this] def earlyHelp = Help(EarlyCommand, EarlyCommandBrief, EarlyCommandDetailed)
 
   def help = Command.make(HelpCommand, helpBrief, helpDetailed)(helpParser)

sbt/src/sbt-test/actions/early-command/build.sbt

@@ -0,0 +1 @@
+lazy val root = (project in file("."))

sbt/src/sbt-test/actions/early-command/test

@@ -0,0 +1 @@
+> early(error)