How to reference a custom SBT Setting in sub-projects - scala

Question

Somewhat similar to this question, how can reference a custom setting in a sub project.
In build.sbt:
import sbt.Keys._
val finagleVersion = settingKey[String]("Defines the Finagle version")
val defaultSettings = Defaults.coreDefaultSettings ++ Seq(
finagleVersion in ThisBuild := "6.20.0",
organization in ThisBuild := "my.package",
scalaVersion in ThisBuild := "2.10.4",
version in ThisBuild := "0.1-SNAPSHOT"
)
lazy val root = project.in(file(".")).aggregate(thrift).settings(
publishArtifact in (Compile, packageBin) := false,
publishArtifact in (Compile, packageDoc) := false,
publishArtifact in (Compile, packageSrc) := false
)
lazy val thrift = project.in(file("thrift"))
In thrift/build.sbt:
name := "thrift"
// doesn't work
libraryDependencies ++= Seq(
"com.twitter" %% "finagle-thriftmux" % (finagleVersion in LocalRootProject).value
)

Answer 1

.sbt files cannot see the definitions (e.g., vals) in other .sbt files, even if they are part of the same build.
However, all .sbt files in a build can see/import the content of project/*.scala files. So you'll have to declare your val finagleVersion in a .scala file:
project/CustomKeys.scala:
import sbt._
import Keys._
object CustomKeys {
val finagleVersion = settingKey[String]("Defines the Finagle version")
}
Now, in your .sbt files, just
import CustomKeys._
and you're good to go.