Deactivate implicits in traits scopes with Dotty

deactivate.scala

import scala.concurrent.ExecutionContext

// this type is used by the implicit search to succeed in finding Not[C]
// when C can not be found as an implicit value
import scala.implicits.Not

trait ImplicitExecutionContextFromExecutionEnv:

  /**
   * if an implicit execution environment is in scope, it can be used as an execution context
   * Here we also expect that no DeactivateImplicitExecutionContext implicit value can be found
   * by requiring Not[DeactivateImplicitExecutionContext]
   */
  given executionEnvToExecutionContext(using ee: ExecutionEnv, not: Not[DeactivateImplicitExecutionContext]) as ExecutionContext =
    ee.executionContext


/**
 * deactivate the conversion between an implicit execution environment to an execution context
 */

// deactivation type
trait DeactivateImplicitExecutionContext

// this trait "deactivates" ImplicitExecutionContextFromExecutionEnv by providing an implicit value
// for the DeactivateImplicitExecutionContext type
trait NoImplicitExecutionContextFromExecutionEnv extends ImplicitExecutionContextFromExecutionEnv:
  
  given deactivateImplicitExecutionContext as DeactivateImplicitExecutionContext =
    new DeactivateImplicitExecutionContext {}

// EXAMPLE

object TryItOk extends ImplicitExecutionContextFromExecutionEnv {
  given ee as ExecutionEnv = ???
  
  // works fine
  summon[ExecutionContext]
}

object TryItKo extends ImplicitExecutionContextFromExecutionEnv with NoImplicitExecutionContextFromExecutionEnv {
  given ee as ExecutionEnv = ???
  
  // fails with 
  //            |Cannot find an implicit ExecutionContext. You might pass
  // [error]    |an (implicit ec: ExecutionContext) parameter to your method.
  summon[ExecutionContext]
}