Add props to define source dependency on io

Use either -Dsbtio.path on the command line
or sbtio.path= in project/local.properties

build.sbt

@@ -83,8 +83,9 @@ lazy val utilComplete = (project in internalPath / "util-complete").
   settings(
     commonSettings,
     name := "Util Completion",
-    libraryDependencies ++= Seq(jline, sbtIO)
-  )
+    libraryDependencies += jline
+  ).
+  configure(addSbtIO)
 
 // logging
 lazy val utilLogging = (project in internalPath / "util-logging").
@@ -117,9 +118,10 @@ lazy val utilCache = (project in internalPath / "util-cache").
   settings(
     commonSettings,
     name := "Util Cache",
-    libraryDependencies ++= Seq(sjsonnew, scalaReflect.value, sbtIO),
+    libraryDependencies ++= Seq(sjsonnew, scalaReflect.value),
     libraryDependencies += sjsonnewScalaJson % Test
-  )
+  ).
+  configure(addSbtIO)
 
 // Builds on cache to provide caching for filesystem-related operations
 lazy val utilTracking = (project in internalPath / "util-tracking").
@@ -127,9 +129,9 @@ lazy val utilTracking = (project in internalPath / "util-tracking").
   settings(
     commonSettings,
     name := "Util Tracking",
-    libraryDependencies += sbtIO,
     libraryDependencies += sjsonnewScalaJson % Test
-  )
+  ).
+  configure(addSbtIO)
 
 // Internal utility for testing
 lazy val utilTesting = (project in internalPath / "util-testing").
@@ -144,12 +146,12 @@ lazy val utilScripted = (project in internalPath / "util-scripted").
   settings(
     commonSettings,
     name := "Util Scripted",
-    libraryDependencies += sbtIO,
     libraryDependencies ++= {
       if (scalaVersion.value startsWith "2.11") Seq(parserCombinator211)
       else Seq()
     }
-  )
+  ).
+  configure(addSbtIO)
 
 def customCommands: Seq[Setting[_]] = Seq(
   commands += Command.command("release") { state =>

project/Dependencies.scala

@@ -5,7 +5,26 @@ object Dependencies {
   lazy val scala211 = "2.11.8"
   lazy val scala212 = "2.12.0-M4"
 
-  lazy val sbtIO = "org.scala-sbt" %% "io" % "1.0.0-M6"
+  private lazy val sbtIO = "org.scala-sbt" %% "io" % "1.0.0-M6"
+
+  def getSbtModulePath(key: String, name: String) = {
+    val localProps = new java.util.Properties()
+    IO.load(localProps, file("project/local.properties"))
+    val path = Option(localProps getProperty key) orElse (sys.props get key)
+    path foreach (f => println(s"Using $name from $f"))
+    path
+  }
+
+  lazy val sbtIoPath = getSbtModulePath("sbtio.path", "sbt/io")
+
+  def addSbtModule(p: Project, path: Option[String], projectName: String, m: ModuleID, c: Option[Configuration] = None) =
+    path match {
+      case Some(f) => p dependsOn c.fold[ClasspathDependency](ProjectRef(file(f), projectName))(ProjectRef(file(f), projectName) % _)
+      case None    => p settings (libraryDependencies += c.fold(m)(m % _))
+    }
+
+  def addSbtIO(p: Project): Project = addSbtModule(p, sbtIoPath, "io", sbtIO)
+
   lazy val jline = "jline" % "jline" % "2.13"
 
   lazy val scalaCompiler = Def.setting { "org.scala-lang" % "scala-compiler" % scalaVersion.value }