Cannot load resource files using Scala / Mill - scala

Question

I cannot load resources in Scala, using Mill (0.10.5) as the build tool.
The minimal example is:
.
├── app
│   └── src
│   └── main
│   ├── resources
│   │   └── hello_world.txt
│   └── scala
│   └── Main.scala
├── build.sc
└── out
with build.sc:
import mill._, scalalib._, mill.modules.Jvm
object app extends ScalaModule {
def scalaVersion = "2.13.5"
}
and Main.scala:
import scala.io.Source
object Main {
def main(args: Array[String]): Unit = {
val helloWorldText : Iterator[String] = Source.fromResource("/hello_world.txt").getLines
helloWorldText.foreach(println)
}
}
While mill -i app.run compiles, the program throws an exception:
Exception in thread "main" java.io.FileNotFoundException: resource 'hello_world.txt' was not found in the classpath from the given classloader
What is the right approach to access resource files using Mill?

Answer 1

Mill ScalaModule does not use the Maven/SBT directory layout by default. Instead, it expects the following directory structure:
.
├── app
│ ├── src
│ | └── Main.scala
│ └── resources
| └── hello_world.txt
├── build.sc
└── out
This is also part of the Getting Started section in the documentation.
What you are looking for is a SBT-compatible project layout, which is discussed in the documentation under section SBT-compatible Modules. In short, you need to extend from SbtModule instead of ScalaModule.
Alternatively, you can also override the sources and resources targets, to customize to your needs.