Question

I have ~6 main classes in my application, by I usually use only one of them, so I wanted to run it automatically by sbt. sbt makes it possible to define two keys in build.sbt:

// Run Key
val selectMainClass = TaskKey[Option[String]]("select-main-class", "Selects the main class to run.")
val mainClass = TaskKey[Option[String]]("main-class", "Defines the main class for packaging or running.")

so I defined them (sample project, two classes – Main1 & Main2 in the root of source dir):

mainClass := Some("Main1")

selectMainClass := Some("Main1") 

And `show main-class’ from sbt prompt also seems to work:

[info] Some(Main1)

But sbt’s run task still prompts me for main class.

Also, sbt-revolver fails to work with multiple classes with exception java.util.NoSuchElementException: None.get

Using sbt 0.11.2.

What am I doing wrong here?

Answer 1

As you can see from using inspect, mainClass is scoped to various configurations and tasks:

> inspect compile:main-class(for run)
[info] Task: scala.Option[java.lang.String]
[info] Description:
[info]  Defines the main class for packaging or running.
[info] Provided by:
[info]  {file:/Users/heiko/tmp/}default-d7f1bf/compile:main-class(for run)
...

Therefore you have to use proper scoping:

set mainClass in (Compile, run) := Some("Foo")