Conditional sbt Settings

build.sbt

scalaVersion := "2.11.7"
crossScalaVersions := Seq("2.9.2", "2.10.5", "2.11.7")

publishTo := Some(Resolver.file("Unused transient repository", file("target/unusedrepo")))

def conditionalSettings[P](conditionalKey: SettingKey[P])(predicate: P => Boolean): Seq[Def.Setting[_]] = {
  // How can I make this suck less?
  Seq(
    publishArtifact := { if(predicate(conditionalKey.value)) false else publishArtifact.value },
    publishLocal := { if(predicate(conditionalKey.value)) {} else publishLocal.value },
    publish := { if(predicate(conditionalKey.value)) {} else publish.value },
    publishTo := { if(predicate(conditionalKey.value)) None else publishTo.value }
  )
}

conditionalSettings(scalaBinaryVersion)(_ == "2.10")

fwiw

val suppressPublishing = settingKey[Boolean]("suppress publishing")
suppressPublishing := scalaBinaryVersion.value == "2.10"

def suppress[T](key: SettingKey[T], value: T): Def.Setting[T] =
  key := { if (suppressPublishing.value) value else key.value }
def suppress[T](key: TaskKey[T], value: T): Def.Setting[Task[T]] =
  key := { if (suppressPublishing.value) value else key.value }

suppress(publish,         {}   )
suppress(publishLocal,    {}   )
suppress(publishArtifact, false)
suppress(publishTo,       None )

Yeah, I went down that path too, but my IRL problem requires value: T to often be a function of other settings, and that's where it fell apart for me.

How about

def conditionalSettings[P](conditionalKey: SettingKey[P])(predicate: P => Boolean): Seq[Def.Setting[_]] = {
    if (predicate(conditionalKey.value))
      Seq(
        publishArtifact := false,
        publishLocal := {},
        publish := {},
        publishTo := None
      )
    else Seq.empty
}

@jastice it won't compile

/path/build.sbt:371: error: `value` can only be used within a task or setting macro, such as :=, +=, ++=, Def.task, or Def.setting.