Conditional libraries in build.sbt - sbt

Question

Using buildsbt. I'm trying to do something like this:
if (condition) {
libraryDependencies += ... // library from maven
}
else {
unmanagedJars in Compile += ... // local library instead
}
However, build.sbt doesn't like this at all. I've been able to accomplish this using side effects, but that's obviously undesirable. Any advice would be appreciated. Thanks.

Answer 1

You can do the following:
val additionalLibraryDependencies = Seq(...)
val additionalUnmanagedJars = Seq(...)
libraryDependencies ++=(
if (condition) {
additionalLibraryDependencies
}
)
unmanagedJars in Compile ++= (
if (!condition) {
additionalUnmanagedJars
}
)
To set the condition from command line you should add the following lines:
val someValueFromCommandLine = System.getProperty("key.of.the.value", "false")
if (someValueFromCommandLine.equals("true")){
...
}
You can pass it like sbt -Dkey.of.the.value=true

Answer 2

This might be easier to do using a Build.scala build definition.
Here is an example build.sbt file (this is optional):
import sbt._
import sbt.Keys._
libraryDependencies ++= Seq(
"org.postgresql" % "postgresql" % "9.3-1101-jdbc41",
"redis.clients" % "jedis" % "2.5.2"
)
Then create another file your_project_home/project/Build.scala
import sbt._
import Keys._
object BuildSettings {
val condition = false
val buildSettings = Defaults.defaultSettings ++ Seq(
version := "1.0.0",
if(condition) libraryDependencies ++= Seq("commons-codec" % "commons-codec" % "1.9")
else unmanagedJars in Compile += file("/tmp/nil")
)
}
object MyBuild extends Build {
import BuildSettings._
lazy val root: Project = Project("root", file("."), settings = buildSettings)
}
Your project structure should look like this:
.
├── build.sbt
├── project
│   └── Build.scala
└── target
You can make the "condition" to be whatever what you need (here I just set it to false). The libraryDependencies defined inside build.sbt will always be included. The ones defined in Build.scala will depend on the "condition."
Verify that everything works as expected from the command line using:
sbt "inspect libraryDependencies"