Additional resource generator with sbt native packager - sbt

Question

I have a submodule, that is compiled by invoking external command. I would like to include generated file into jar. So I wrote a task:
```
myTask := {
import sys.process.stringSeqToProcess
Seq("my", "command") !
}
unmanagedResourceDirectories in Compile += baseDirectory.value / "dist"
cleanFiles <+= baseDirectory { base => base / "dist" }
Keys.`package` <<= (Keys.`package` in Compile) dependsOn npmBuildTask.toTask
and when I invoke mySubmodule/package task it works well. But when I invoke stage task from sbt-native-packager my task is ignored(is not executed).

Answer 1

There are a couple of options to solve this issue. I assume you want to add the dist folder to your resulting application jar.
Your configuration doesn't work because stage doesn't depend on package. This results npmBuildTask not being called.
1. Add dependency to stage
The easiest way to fix this is by simply adding the npmBuildTask as a dependency to stage
stage <<= stage dependsOn npmBuildTask.toTask
I wouldn't recommend this approach.
2. Resource generators
SBTs Resoure Generators are exactly defined for this purpose. An inline version could look like this
resourceGenerators in Compile += Def.task {
streams.value.log.info("running npm generator")
val base = (resourceManaged in Compile).value / "dist"
// A resource generator returns a Seq[File]. This is just an example
List("index.js", "test.js").map { file =>
IO.writeLines(base / file, List("var x = 1"))
base / file
}
}.taskValue
Or you could extract this in an AutoPlugin to separate the "what" and "how.
3. AutoPlugin and resource generators
Create project/NpmPlugin.scala and add the following content
import sbt._
import sbt.Keys._
import sbt.plugins.JvmPlugin
object NpmPlugin extends AutoPlugin {
override val requires = JvmPlugin
override val trigger = AllRequirements
object autoImport {
val npmBuildTask = TaskKey[Seq[File]]("npm-build-task", "Runs npm and builds the application")
}
import autoImport._
override def projectSettings: Seq[Setting[_]] = Seq(
// define a custom target directory for npm
target in npmBuildTask := target.value / "npm",
// the actual build task
npmBuildTask := {
val npmSource = (target in npmBuildTask).value
val npmTarget = (resourceManaged in Compile).value / "dist"
// run npm here, which generates the necessary values
streams.value.log.info("running npm generator")
// move generated sources to target folder
IO.copyDirectory(npmSource, npmTarget)
// recursively get all files in the npmTarget
(npmTarget ***).get
},
resourceGenerators in Compile += npmBuildTask.taskValue
)
}
The build.sbt will then look like this
name := "resource-gen-test"
version := "1.0"
enablePlugins(JavaAppPackaging)
Pretty clean :)
4. Use mappings
Last but not least you could use mappings. They are the low level detail that drives a lot of the package-generation in sbt. The main idea of this solution is to
Create a task that returns a mapping definition ( Seq[(File, String)] )
Append this to the appropriate mappings
The advantage of this approach is that you are more flexible where you want to put your mappings.
import sbt._
import sbt.Keys._
import sbt.plugins.JvmPlugin
import com.typesafe.sbt.SbtNativePackager.Universal
import com.typesafe.sbt.SbtNativePackager.autoImport.NativePackagerHelper._
object NpmMappingsPlugin extends AutoPlugin {
override val requires = JvmPlugin
override val trigger = AllRequirements
object autoImport {
val npmBuildTask = TaskKey[Seq[(File, String)]]("npm-build-task", "Runs npm and builds the application")
}
import autoImport._
override def projectSettings: Seq[Setting[_]] = Seq(
// define a custom target directory for npm
target in npmBuildTask := target.value / "npm" / "dist",
// the actual build task
npmBuildTask := {
val npmTarget = (target in npmBuildTask).value
// run npm here, which generates the necessary values
streams.value.log.info("running npm generator")
// recursively get all files in the npmTarget
// contentOf(npmTarget) would skip the top-level-directory
directory(npmTarget)
},
// add npm resources to the generated jar
mappings in (Compile, packageBin) ++= npmBuildTask.value,
// add npm resources to resulting package
mappings in Universal ++= npmBuildTask.value
)
}
As you can see in this approach we can easily add the resulting files to different mappings.
However I only recommend this approach if you need this kind of flexibility as it requires a bit more knowledge of native-packager.