sbt, libraryDependencies without groupID and revision?

Question

From sbt documentation , the libraryDependencies format is:

libraryDependencies += groupID % artifactID % revision

For example:

libraryDependencies += "org.postgresql" % "postgresql" % "42.1.4"

However, in the Play 2.6.x Scala Starter Example project, the guice libraryDependencies in build.sbt shows only

libraryDependencies += guice

How do we know which guice version will be adopted by sbt or the format is for some specific purpose?

Answer 1

When you use Play Framework, you normally setup your project using the special sbt plugin . You should have it in your project/plugins.sbt :

addSbtPlugin("com.typesafe.play" % "sbt-plugin" % "...")

This plugin defines values for different optional dependencies such as guice in your question. So you can go to the sbt plugin source and check what is this guice exactly ( here ):

val guice = component("play-guice")

And component is defined as

def component(id: String) = "com.typesafe.play" %% id % play.core.PlayVersion.current

So it actually refers to the play-guice subproject of the Play framework and it depends on guiceDeps , which are defined in the playframework/framework/project/Dependencies.scala :

val guiceVersion = "4.2.0"
val guiceDeps = Seq(
  "com.google.inject" % "guice" % guiceVersion,
  "com.google.inject.extensions" % "guice-assistedinject" % guiceVersion
)

---

This is just to show where does it come from. Normally, when you want to check your transitive dependencies, you should use sbt-dependency-graph plugin. It can list all your dependencies (with their versions and other useful information) in the sbt shell or visualize it as a tree or a graph.