Setting a third-party plugin setting in sbt AutoPlugin - scala

Question

I have an AutoPlugin which aggregates several third-party plugins and customizes their settings for our company. For most of the plugins, this works just fine by putting them in the projectSettings:
override lazy val projectSettings = Seq( somePluginSetting := "whatever" )
I tried to do this for ScalaStyle as well:
import org.scalastyle.sbt.ScalastylePlugin.scalastyleConfigUrl
override lazy val projectSettings = Seq(
scalastyleConfigUrl := Some(url("http://git.repo/scalastyle-config.xml"))
)
This setting is never visible in projects using my plugin, instead sbt uses the plugin-provided default value:
> inspect scalastyleConfigUrl
[info] Setting: scala.Option[java.net.URL] = None
[info] Description:
[info] Scalastyle configuration file as a URL
[info] Provided by:
[info] {file:/Users/kaeser/Documents/workspace/ci-test-project/}root/*:scalastyleConfigUrl
[info] Defined at:
[info] (org.scalastyle.sbt.ScalastylePlugin) Plugin.scala:101
[info] Delegates:
[info] *:scalastyleConfigUrl
[info] {.}/*:scalastyleConfigUrl
[info] */*:scalastyleConfigUrl
[info] Related:
[info] test:scalastyleConfigUrl
When I put the setting into build.sbt directly, it works as expected.
I made a simple example sbt plugin that shows the problem: https://github.com/jastice/sbt-customsettings
What might the issue be?

Answer 1

This problem is most likely caused by the order in which settings are applied. If your plugin and the plugin you are depending on are both autoplugins, the requires value determines the order in which project settings are included.
Scalastyle still uses the old plugin format. It also does not follow the best practices. It should not set projectSettings as that makes it difficult to disable it in multi project builds. And it also prevents you from easily extending it from your custom plugin. I am not sure if the order in which project settings are applied is defined, or is determined by the order in which the plugins are loaded.
The easiest fix would be to make Scalastyle an AutoPlugin and depend on it using the requires value. Otherwise it's probably quite tricky to find out what determines the order.