Unable to call other tasks from test command

[ex0ns]

In a pretty simple build definition, I was trying to override the test method of a module, and I don't understand why what I am trying to perform is not valid:

import mill._
import scalalib._


object core extends ScalaModule {
  def scalaVersion = "2.13.11"

  object test extends ScalaTests with TestModule.ScalaTest {
    def other = T {
      T.log.info("Other log")
    }

    def test(args: String*) = T.command {
      other()
      T.log.info("Running test")
      super.test()
    }
  }
}

[error] /Users/ex0ns/tmp/build.sc:22:12: Target#apply() can only be used with a T{...} block
[error]       other()
[error]            ^
[error] /Users/ex0ns/tmp/build.sc:23:9: Target.ctx() / T.ctx() / T.* APIs can only be used with a T{...} block
[error]       T.log.info("Running test")
[error]         ^
[error] two errors found

whereas if I defined another target, with the same signature, it works fine:

def mytest(args: String*) = T.command { 
  T.log.info("test")
}

[lefou]

The issue with your attempt is, that you don't depend on the result of the super.test() command, but instead return the command itself. Or in other words, you forgot the second ().

 def test(args: String*) = T.command {
       other()
       T.log.info("Running test")
-      super.test()
+      super.test()()
     }

As T.command accepts a Task and you already return a task, you essentially return that super.test task and also access the T.log.info outside of a task, which is not possible. Hence, the somewhat unhelpful error message.

To use a task's outcome, you always add one addition parenthesis pair more than on the definition side.
This is the short for task.apply(). For commands, that don't need any arguments, that means you have two parenthesis pairs. The first holding the (empty) command arguments, and the second actually refering the the result value of that command.

[lefou]

Please note, that the T.log.info("Running test") will always run after the super.test, due to the fact that the test task depends on the result of the super.test.

[ex0ns]

It makes sense now that you explain it like that, what is pretty confusing is how changing super.test() to super.test()() could have an impact on the "previous line".

As always, thanks for the explanation