How to create scala-cli type of "lightweight launcher JAR" from a project?

[jk-1]

How can I create a "lightweight launcher JAR" from my project with mill?
I.e. How to create a single executable file same way as scala-cli package mySource.scala produces?

See default package format: https://scala-cli.virtuslab.org/docs/commands/package

[lihaoyi]

Probably ./mill foo.assembly?

[jk-1]

I think they are not same thing.

The mill assembly command creates fat jar that I can run offline
while scala-cli package creates smaller executable file which downloads missing pieces if they do not exist.

The default package format writes a lightweight launcher JAR, like the "bootstrap" JAR files generated by coursier. These JARs tend to have a small size (mostly containing only the byte code from your own sources), can be generated fast, and download their dependencies upon first launch via coursier.

See below a small example: HelloScript.sc

val sv = scala.util.Properties.versionNumberString

val message = s"Hello from Scala ${sv}, Java ${System.getProperty("java.version")}"
println(message)
println("args: " + args.toSeq)

ll out/project/assembly.dest/out*
-rwx--x--x 1 jk jk 7300804 heinä   1 15:52 out/project/assembly.dest/out.jar*

ll HelloScript
-rwx------ 1 jk jk 171427 heinä   1 15:54 HelloScript*

[lihaoyi]

Oh you want a dependency-downloading bootstrapper. Mill does not have that built in. You should be able to implement it as a custom task in your own build I think