fix dependsOn not propagating failures in dependencies

main/Structure.scala

@@ -207,8 +207,7 @@ object Scoped
 		{
 			val in = KCons(scopedTask(scope, key), KList.fromList(tasks))
 			Apply.tasks(in) { kl =>
-				val KCons(h,t) = KList.kcons(kl)
-				h.dependsOn(t.toList :_*)
+				kl.head.dependsOn(kl.tail.toList :_*)
 			}
 		}
 	}

sbt/src/sbt-test/actions/depends-on/project/B.scala

@@ -0,0 +1,17 @@
+import sbt._
+import Keys._
+
+// tests that errors are properly propagated for dependsOn, map, and flatMap
+object B extends Build
+{
+	lazy val root = Project("root", file(".")) settings(
+		a <<= baseDirectory map (b =>  if( (b / "succeed").exists) () else error("fail")),
+		b <<= a.task(at => nop dependsOn(at) ),
+		c <<= a map { _ => () },
+		d <<= a flatMap { _ => task { () } }
+	)
+	lazy val a = TaskKey[Unit]("a")
+	lazy val b = TaskKey[Unit]("b")
+	lazy val c = TaskKey[Unit]("c")
+	lazy val d = TaskKey[Unit]("d")
+}

sbt/src/sbt-test/actions/depends-on/test

@@ -0,0 +1,8 @@
+-> a
+-> b
+-> c
+
+$ touch succeed
+> a
+> b
+> c

tasks/standard/System.scala

@@ -6,6 +6,7 @@ package std
 
 import Types._
 import Task._
+import TaskExtra.allM
 import Execute._
 
 object Transform
@@ -46,7 +47,7 @@ object Transform
 			case Pure(eval) => toNode(KNil)( _ => Right(eval()) )
 			case Mapped(in, f) => toNode(in)( right ∙ f  )
 			case FlatMapped(in, f) => toNode(in)( left ∙ f )
-			case DependsOn(in, deps) => toNode(KList.fromList(deps))( _ => Left(in) )
+			case DependsOn(in, deps) => toNode(KList.fromList(deps))( ((_:Any) => Left(in)) ∙ allM )
 			case Join(in, f) => uniform(in)(f)
 		}
 	}