Consider adding -Ywarn-macros:after about sbt-tpolecat HOT 6 CLOSED

OK, let's close this for now 👍

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Ah I wasn't aware of this flag, this is a great idea - my only question is whether it would be problematic to cause warnings in expanded macros since users cannot do anything about it? Perhaps -Wwarn-macros:none might be the best choice?

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That would not solve the first problem and would add extra problems.

The original problem is something like this:

import io.circe.Encoder
import io.circe.generic.semiauto.deriveEncoder
import io.circe.syntax._

final case class A(i: Int)
final case class B(name: String, a: A)

implicit val AEncoder: Encoder[A] = deriveEncoder
implicit val BEncoder: Encoder[B] = deriveEncoder

B(name = "Test", a = A(i = 10)).asJson.noSpaces

If you compile this snippet with the plugin. You would get an unused value warning for AEncoder which will be turn on an error. Thus, it would not compile.
The problem is that AEncoder is only used for the derivation of BEncoder, which happens inside a macro, that has not being expanded when the unused analysis is executed.
To solve it, you would have to manually add the -Ywarn-macros:after flag. So the check for unused values is executed after the macros had been expanded.

As far as I know, this should not cause problems to final users, unless the macro is leaving unused values (I would hope that is uncommon). The only downside I see is, slower compilation times.

As I already said -Ywarn-macros:none would not only not solve this problems, but cause more.
Consider this code:

import com.typesafe.scalalogging.StrictLogging

object Main extends App with StrictLogging {
  val testMessage = "Hello, World!"
  logger.info(testMessage)
}

Since testMessage is only used inside the logger.info method, which is in turn a macro, it would be marked as an unused value.

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It seems there are good reasons (at least from a theoretical point of view) for leaving before as the default.

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In that case perhaps we should leave it as -Wmacros:before until such time as there is a -Wmacros:either option, which sounds like it would be the most ideal option here?

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@DavidGregory084 I think the better is to just leave it as it is right now. That way if a user needs it, he / she can just add the setting explicitly.

I may be nice if the plugin offers some way to activate / deactivate this one.
Maybe something like: warnAfterMacros in tpolecat := true but I am not sure how much of an improvement that would be.
(unless a similar flag is also added for #10 then it would be worth adding this)

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