Def.taskIf macro

Def.taskIf accepts an if-expression or a block ending in an if-expression.

main-settings/src/main/scala/sbt/Def.scala

@@ -221,6 +221,7 @@ object Def extends Init[Scope] with TaskMacroExtra with InitializeImplicits {
     inputTaskDynMacroImpl,
     inputTaskMacroImpl,
     taskDynMacroImpl,
+    taskIfMacroImpl,
     taskMacroImpl
   }
   import std._
@@ -234,6 +235,7 @@ object Def extends Init[Scope] with TaskMacroExtra with InitializeImplicits {
   def inputTask[T](t: T): Def.Initialize[InputTask[T]] = macro inputTaskMacroImpl[T]
   def inputTaskDyn[T](t: Def.Initialize[Task[T]]): Def.Initialize[InputTask[T]] =
     macro inputTaskDynMacroImpl[T]
+  def taskIf[T](a: Def.Initialize[Task[T]]): Def.Initialize[Task[T]] = macro taskIfMacroImpl[T]
 
   private[sbt] def selectITask[A, B](
       fab: Initialize[Task[Either[A, B]]],

main-settings/src/main/scala/sbt/std/TaskMacro.scala

@@ -118,6 +118,21 @@ object TaskMacro {
       Instance.idTransform[c.type]
     )
 
+  def taskIfMacroImpl[A: c.WeakTypeTag](
+      c: blackbox.Context
+  )(a: c.Expr[Initialize[Task[A]]]): c.Expr[Initialize[Task[A]]] = {
+    import c.universe._
+    def mkIfS(cond: Tree, thenp: Tree, elsep: Tree): Tree =
+      q"""Def.ifS(Def.task($cond))($thenp)($elsep)"""
+    a.tree match {
+      case Block(stat, If(cond, thenp, elsep)) =>
+        c.Expr[Initialize[Task[A]]](mkIfS(Block(stat, cond), thenp, elsep))
+      case If(cond, thenp, elsep) =>
+        c.Expr[Initialize[Task[A]]](mkIfS(cond, thenp, elsep))
+      case x => ContextUtil.unexpectedTree(x)
+    }
+  }
+
   /** Implementation of := macro for settings. */
   def settingAssignMacroImpl[T: c.WeakTypeTag](
       c: blackbox.Context

main/src/main/scala/sbt/Defaults.scala

@@ -2128,9 +2128,10 @@ object Defaults extends BuildCommon {
     )
 
   def dependencyResolutionTask: Def.Initialize[Task[DependencyResolution]] =
-    Def.ifS(useCoursier.toTask)(Def.task { CoursierDependencyResolution(csrConfiguration.value) })(
-      Def.task { IvyDependencyResolution(ivyConfiguration.value, CustomHttp.okhttpClient.value) }
-    )
+    Def.taskIf {
+      if (useCoursier.value) Def.task { CoursierDependencyResolution(csrConfiguration.value) } else
+        Def.task { IvyDependencyResolution(ivyConfiguration.value, CustomHttp.okhttpClient.value) }
+    }
 }
 
 object Classpaths {
@@ -2947,14 +2948,18 @@ object Classpaths {
     publishTask(config)
 
   def publishTask(config: TaskKey[PublishConfiguration]): Initialize[Task[Unit]] =
-    Def.ifS((publish / skip).toTask)(Def.task {
-      val s = streams.value
-      val ref = thisProjectRef.value
-      s.log.debug(s"Skipping publish* for ${ref.project}")
-    })(Def.task {
-      val s = streams.value
-      IvyActions.publish(ivyModule.value, config.value, s.log)
-    }) tag (Tags.Publish, Tags.Network)
+    Def.taskIf {
+      if ((publish / skip).value)
+        Def.task {
+          val s = streams.value
+          val ref = thisProjectRef.value
+          s.log.debug(s"Skipping publish* for ${ref.project}")
+        } else
+        Def.task {
+          val s = streams.value
+          IvyActions.publish(ivyModule.value, config.value, s.log)
+        }
+    } tag (Tags.Publish, Tags.Network)
 
   val moduleIdJsonKeyFormat: sjsonnew.JsonKeyFormat[ModuleID] =
     new sjsonnew.JsonKeyFormat[ModuleID] {

sbt/src/sbt-test/actions/ifs/build.sbt

@@ -11,7 +11,10 @@ lazy val root = (project in file("."))
     condition := true,
     trueAction := { IO.write(output.value, s"true\n", append = true) },
     falseAction := { IO.write(output.value, s"false\n", append = true) },
-    foo := (Def.ifS(condition)(trueAction)(falseAction)).value,
+    foo := (Def.taskIf {
+      if (condition.value) trueAction
+      else falseAction
+    }).value,
     TaskKey[Unit]("check") := {
       val lines = IO.read(output.value).linesIterator.toList
       assert(lines == List("true"))