Built-in support for per-sourceset configurable failure thresholds

[TheMrMilchmann]

It would be nice if we could configure different failure thresholds per sourcesets. My use case would be permitting low-priority violations in tests. This is somewhat possible by manually wiring up an extra EnforceArchRulesTask (and excluding the test source-set from the standard logic), but this feels a bit hacky and like something that should be supported out of the box.

Introducing a mechanism for per-sourceset configuration would give far greater freedom and would blend naturally with Gradle's NamedDomainObjectCollection API.

[wakingrufus]

This seems feasible. It would take a fairly significant refactor of the enforce task though, since it reads the data files without really knowing which source sets they came from. but this type of refactor could also help us point to source locs in the Problems API as well, so it might be worth doing

[TheMrMilchmann]

Another possible solution for the configuration (that I didn't consider when writing the issue) would be registering an extension against each SourceSet. A rough example of how I'm doing this in a different (as of yet unpublished) plugin:

// Provide an extension function for this to work nicely with the Kotlin DSL
public fun SourceSet.optIn(action: Action<OptInSourceSetExtension>) {
    this.extensions.configure(OptInSourceSetExtension::class.java, action)
}

public interface OptInSourceSetExtension { /* ... */ }

// Register the extension in the plugin
sourceSets.configureEach {
    val optInSourceSetExtension = extensions.create(...)
    // ...
}

As for the enforce task, I wonder if it would be feasible to have one task per sourceset and an "umbrella" task that depends on all of them. The main issue with this approach would be that checking the results across all source sets would require using --continue.