sbt: dynamic aggregation of subproject

Question

I would like to invent a system to dynamically discover subprojects and aggregate them into my project automatically. Or at least configure this somehow.

Answer 1

Here:

project/Build.scala

import sbt._
import sbt.Keys._

import play.sbt._
import play.sbt.Play.autoImport._

object Build extends Build {
  val commonSettings: Seq[Setting[_]] = Seq(
    scalaVersion := "2.11.7"
  )

  lazy val modules = (file("modules") * DirectoryFilter).get.map { dir =>
    Project(dir.getName, dir).enablePlugins(PlayJava).settings(commonSettings: _*)
  }

  lazy val root = (project in file("."))
    .enablePlugins(PlayJava)
    .settings(
      name := "mysite",
      version := "1.0"
    )
    .settings(commonSettings: _*)
    .dependsOn(modules map (m => m: ClasspathDependency): _*)
    .aggregate(modules map (m => m: ProjectReference): _*)

  override lazy val projects = root +: modules
}

Note, make sure that the module directories don't also contain build.sbt files defining them as projects as that will cause confusing RuntimeException: No project 'x' in 'file:/x' type exception, see Can't use sbt 0.13.7 with Play subprojects

Answer 2

You can try something like this:

import sbt._
import sbt.Keys._

import play.sbt._
import play.sbt.Play.autoImport._

object Build extends Build {

  lazy val modules = (file("modules") * DirectoryFilter).get.map { dir =>
    Project(dir.getName, dir).enablePlugins(PlayJava)
  }

  lazy val root = (project in file("."))
    .enablePlugins(PlayJava)
    .settings(
      name := "mysite",
      version := "1.0"
    )
    .dependsOn(modules map (m => m: ClasspathDependency): _*)
    .aggregate(modules map (m => m: ProjectReference): _*)

  override lazy val projects = root +: modules
}

Note: Inspired by Dale's answer, but I had to remove the "commonSettings", otherwise it would not work for me.