Why does the default run task not pick settings in custom configuration? - sbt

Question

I use sbt 0.13.6-SNAPSHOT built from the latest sources as of commit 5b070b9dcc1dea25106573a86167517e5a8dc8d4.
The issue came out when I was responding to How to change value of setting for a custom configuration under play/sbt?.
This is build.sbt:
lazy val Mock = config("mock") extend Compile
lazy val mock = inputKey[Unit]("run in mock mode")
lazy val mockSettings = inConfig(Mock) {
Classpaths.configSettings ++
Seq(
unmanagedClasspath += baseDirectory.value / "mock-resources",
mock <<= run in Mock,
run <<= Defaults.runTask(fullClasspath in Mock, mainClass in Mock, runner in Mock)
)
}
lazy val p = (project in file("src/")).configs(Mock).settings(
mockSettings: _*
)
Why is the custom run task needed for the custom Mock configuration? Why doesn't run pick unmanagedClasspath for the Mock configuration?
See the following session:
> mock
[info] Running Hello
resource: file:/Users/jacek/sandbox/mock-config/src/mock-resources/a.properties
[success] Total time: 0 s, completed Jul 27, 2014 2:26:07 PM
> p/mock:run
[info] Running Hello
resource: file:/Users/jacek/sandbox/mock-config/src/mock-resources/a.properties
[success] Total time: 0 s, completed Jul 27, 2014 2:26:34 PM
> p/mock:mock
[info] Running Hello
resource: file:/Users/jacek/sandbox/mock-config/src/mock-resources/a.properties
[success] Total time: 0 s, completed Jul 27, 2014 2:27:01 PM
It works fine.
The following line gets removed from build.sbt:
run <<= Defaults.runTask(fullClasspath in Mock, mainClass in Mock, runner in Mock)
This is the only change for the build definition. No other files are touched.
> reload
[info] Loading global plugins from /Users/jacek/.sbt/0.13/plugins
[info] Set current project to mock-config (in build file:/Users/jacek/sandbox/mock-config/)
> p/mock:mock
[info] Running Hello
resource: null
[success] Total time: 0 s, completed Jul 27, 2014 2:28:31 PM
> p/mock:run
[info] Running Hello
resource: null
[success] Total time: 0 s, completed Jul 27, 2014 2:28:36 PM
> mock
[info] Running Hello
resource: null
[success] Total time: 0 s, completed Jul 27, 2014 2:28:39 PM
Why does the default run task not work for the custom Mock configuration?

Answer 1

Please use a released version to ask questions such as 0.13.5.
If you run inspect command, it should be clear that you have not defined run task when you remove run <<= .... from build.sbt:
p> inspect mock:run
[info] Input task: Unit
[info] Description:
[info] Runs a main class, passing along arguments provided on the command line.
[info] Provided by:
[info] {file:/Users/foo/sbt-so-24981062/}p/compile:run
[info] Defined at:
[info] (sbt.Defaults) Defaults.scala:731
This is because Classpaths.configSettings doesn't include run task.