Do not require leading semicolon for multi command

It has long been a frustration of mine that it is necessary to prepend
multiple commands with a ';'. In this commit, I relax that restriction.
I had to reorder the command definitions so that multi comes before act.
This was because if the multi command did not have a leading semicolon,
then it would be handled by the action parser before the multi command
parser had a shot at it. Sadness ensued.

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

@@ -39,7 +39,6 @@ object BasicCommands {
     ignore,
     help,
     completionsCommand,
-    multi,
     ifLast,
     append,
     setOnFailure,
@@ -164,7 +163,10 @@ object BasicCommands {
     )
     def commandParser = state.map(s => (s.combinedParser & cmdPart) | cmdPart).getOrElse(cmdPart)
     val part = semi.flatMap(_ => matched(commandParser) <~ token(OptSpace)).map(_.trim)
-    part.+ map (_.toList)
+    (cmdPart.? ~ part.+).map {
+      case (Some(h), t) => h.mkString.trim +: t.toList
+      case (_, t)       => t.toList
+    }
   }
 
   def multiParser(s: State): Parser[List[String]] = multiParserImpl(Some(s))

main-command/src/test/scala/sbt/MultiParserSpec.scala

@@ -14,6 +14,7 @@ object MultiParserSpec {
   val parser: Parser[Seq[String]] = BasicCommands.multiParserImpl(None)
   implicit class StringOps(val s: String) {
     def parse: Seq[String] = Parser.parse(s, parser).right.get
+    def parseEither: Either[String, Seq[String]] = Parser.parse(s, parser)
   }
 }
 import MultiParserSpec._
@@ -45,4 +46,20 @@ class MultiParserSpec extends FlatSpec with Matchers {
     """; setStringValue "foo;bar"; checkStringValue "foo;bar"""".parse shouldBe
       Seq("""setStringValue "foo;bar"""", """checkStringValue "foo;bar"""")
   }
+  it should "parse commands without leading ';'" in {
+    "setStringValue foo; setStringValue bar".parse shouldBe Seq(
+      "setStringValue foo",
+      "setStringValue bar"
+    )
+    "foo; bar".parse shouldBe Seq("foo", "bar")
+    "foo bar ;bar".parse shouldBe Seq("foo bar", "bar")
+    "foo \"a;b\"; bar".parse shouldBe Seq("foo \"a;b\"", "bar")
+    " foo ; bar \"b;c\"".parse shouldBe Seq("foo", "bar \"b;c\"")
+  }
+  it should "not parse single commands without leading ';'" in {
+    "foo".parseEither shouldBe Left("Expected ';'\nfoo\n   ^")
+    "foo bar baz".parseEither shouldBe Left("Expected ';'\nfoo bar baz\n           ^")
+    "foo bar baz;".parseEither shouldBe
+      Left("Expected not ';'\nExpected '\"'\nfoo bar baz;\n            ^")
+  }
 }

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

@@ -241,6 +241,7 @@ object BuiltinCommands {
       export,
       boot,
       initialize,
+      BasicCommands.multi,
       act,
       continuous,
       flushFileTreeRepository

sbt/src/sbt-test/actions/multi-command/test

@@ -7,3 +7,15 @@
 > checkStringValue bar
 
 > ; setStringValue foo; setStringValue bar; setStringValue baz; checkStringValue baz
+
+> setStringValue foo; setStringValue bar
+
+> checkStringValue bar
+
+> setStringValue foo; setStringValue bar; setStringValue baz
+
+> checkStringValue baz
+
+-> setStringValue foo; taskThatFails; setStringValue bar
+
+> checkStringValue foo

sbt/src/sbt-test/watch/watch-parser/test

@@ -8,6 +8,9 @@
 
 > ~; setStringValue foo; setStringValue bar; checkStringValue bar
 
+# no leading semicolon
+> ~ setStringValue foo; setStringValue bar; checkStringValue bar
+
 > ~ setStringValue foo
 
 > checkStringValue foo