Don't create too visible empty directories during build

build.sbt

@@ -137,7 +137,7 @@ lazy val web = project
       if (scalaBinaryVersion.value == "2.11")
         dir
       else
-        dir / "dummy"
+        dir / "target" / "dummy"
     },
     noTests,
     webjarBintrayRepository,
@@ -226,6 +226,7 @@ lazy val echo = project
   .settings(shared)
 
 lazy val jvm = project
+  .dummy
   .aggregate(
     coreJvm,
     testsJvm,
@@ -248,6 +249,7 @@ lazy val jvm = project
   )
 
 lazy val js = project
+  .dummy
   .aggregate(
     coreJs,
     `fetch-js`,

project/Aliases.scala

@@ -18,4 +18,10 @@ object Aliases {
 
   def ShadingPlugin = coursier.ShadingPlugin
 
+
+  implicit class ProjectOps(val proj: Project) extends AnyVal {
+    def dummy: Project =
+      proj.in(file(s"target/${proj.id}"))
+  }
+
 }

project/Settings.scala

@@ -162,7 +162,7 @@ object Settings {
         if (sbtScalaVersionMatch.value)
           baseDirectory.value
         else
-          baseDirectory.value / "dummy"
+          baseDirectory.value / "target" / "dummy"
       },
       publish := {
         if (sbtScalaVersionMatch.value)