How to publish an artifact with pom-packaging in SBT? - sbt

Question

I have a multi-project build in SBT where some projects should aggregate dependencies and contain no code. So then clients could depend on these projects as a single dependency instead of directly depending on all of their aggregated dependencies. With Maven, this is a common pattern, e.g. when using Spring Boot.
In SBT, I figured I can suppress the generation of the empty artifacts by adding this setting to these projects:
packagedArtifacts := Classpaths.packaged(Seq(makePom)).value
However, the makePom task writes <packaging>jar</packaging> in the generated POM. But now that there is no JAR anymore, this should read <packaging>pom</packaging> instead.
How can I do this?

Answer 1

This question is a bit old, but I just came across the same issue and found a solution. The original answer does point to the right page where this info can be found, but here is an example. It uses the pomPostProcess setting to transform the generated POM right before it is written to disk. Essentially, we loop over all the XML nodes, looking for the element we care about and then rewrite it.
import scala.xml.{Node => XmlNode, NodeSeq => XmlNodeSeq, _}
import scala.xml.transform._
pomPostProcess := { node: XmlNode =>
val rule = new RewriteRule {
override def transform(n: XmlNode): XmlNodeSeq = n match {
case e: Elem if e != null && e.label == "packaging" =>
<packaging>pom</packaging>
case _ => n
}
}
new RuleTransformer(rule).transform(node).head
},

Answer 2

Maybe you could modify the result pom as described here: Modifying the generated POM

Answer 3

You can disable publishing the default artifacts of JAR, sources, and docs, then opt in explicitly to publishing the POM. sbt produces and publishes a POM only, with <packaging>pom</packaging>.
// This project has no sources, I want <packaging>pom</pom> with dependencies
lazy val bundle = project
.dependsOn(moduleA, moduleB)
.settings(
publishArtifact := false, // Disable jar, sources, docs
publishArtifact in makePom := true,
)
lazy val moduleA = project
lazy val moduleB = project
lazy val moduleC = project
Run sbt bundle/publishM2 to verify the POM in ~/.m2/repository.
I dare say this is almost intuitive, a rare moment of pleasant surprise with sbt 😅
I confirmed this with current sbt 1.3.9, and 1.0.1, the oldest launcher I happen to have installed on my machine.
The Artifacts page in the reference docs may be helpful, perhaps this trick should be added there.