smithy-trait-codegen-scala

Generate Java classes (with builders, serialization to/from Node, trait providers) for Smithy traits, for usage in Scala projects.

Usage

sbt

In project/plugins.sbt:

addSbtPlugin("org.polyvariant" % "smithy-trait-codegen-sbt" % version)

In build.sbt:

// on a Java-only module, e.g. autoScalaLibrary := false, crossPaths := false
.enablePlugins(SmithyTraitCodegenPlugin)
.settings(
  smithyTraitCodegenDependencies := Nil,
  smithyTraitCodegenNamespace := "my.ns",
  // Note: this is the "root" package of generated output.
  // Sub-namespaces of my.ns will be generated as sub-packages of this package, as seen from my.ns.
  // For example, my.ns.foo will be generated as my.pkg.foo.
  smithyTraitCodegenJavaPackage := "my.pkg",
)

mill

Currently not supported in this plugin. See https://github.com/simple-scala-tooling/smithy-trait-codegen-mill/ for an alternative.

Useful patterns

Mixing generated and handwritten providers

In case you want to keep some handwritten trait providers, e.g. if you have union traits (which are currently not supported in smithy-trait-codegen), or want to keep binary compatibility on existing traits.

Instead of META-INF/services/software.amazon.smithy.model.traits.TraitService, add the providers to

META-INF/services-input/software.amazon.smithy.model.traits.TraitService

and add this snippet to include those in the actual, generated file under META-INF/services:

smithyTraitCodegenExternalProviders ++=
  IO.readLines(
    (ThisBuild / baseDirectory).value / "modules" / "protocol" / "resources" / "META-INF" / "services-input" / classOf[TraitService].getName()
  ).filterNot(_.trim.startsWith("#"))
    .filterNot(_.trim.isEmpty),
Compile / packageBin / mappings ~= {
  _.filterNot { case (_, path) => path.contains("services-input") }
}

You can also hardcode smithyTraitCodegenExternalProviders right there:

smithyTraitCodegenExternalProviders ++= List("my.pkg.Trait1$Provider", "my.pkg.Trait2$Provider")