Wconf/nowarn do not work for compiler plugins

[neko-kai]

reproduction steps

using Scala 2.13.4,

@scala.annotation.nowarn("msg=kind-projector")
object x extends App {
  class OptionT[F[_], A]
  def xa(f: OptionT[Option[?], Int]) = ()
}

https://scastie.scala-lang.org/epxMf0GETwKx2sOIp9rkKA

problem

This produces a warning

kind-projector ? placeholders are deprecated. Use * instead of ? for cross-compatibility with Scala 3

Despite nowarn annotation filtering it. The same applies to -Wconf:msg=kind-projector:silent

expectation

Expected compiler-plugin generated warnings to also be ignored

[sjrd]

That's because the compiler plugins emit warnings in the old way, which the warning configuration system cannot see/tweak. Compiler plugins need to be adapted to call the overload of warning that takes a Category and a site. For example:
https://github.com/scala-js/scala-js/blob/950fcda1e480d54b50e75f4cce5bd4135cb58a53/compiler/src/main/scala/org/scalajs/nscplugin/GenJSCode.scala#L401-L407

To be able to write this in a source-compatible way with all versions of the compiler API, they can use the following hacks:
https://github.com/scala-js/scala-js/blob/950fcda1e480d54b50e75f4cce5bd4135cb58a53/compiler/src/main/scala/org/scalajs/nscplugin/CompatComponent.scala#L43-L55
https://github.com/scala-js/scala-js/blob/950fcda1e480d54b50e75f4cce5bd4135cb58a53/compiler/src/main/scala/org/scalajs/nscplugin/CompatComponent.scala#L114-L132

[neko-kai]

@sjrd This could be supported on the backend, too though, since msg= filter does not require category.

[sjrd]

It doesn't require a category, but it requires a site (at least for @nowarn, not for the compiler flag -Wconf).

[neko-kai]

Makes sense, -Wconf ought to work in theory but fails to catch this case too (https://scastie.scala-lang.org/wC42UzZ3T2i0l0sq19ubqw)

[NthPortal]

this seems like something for which @som-snytt might have insight

[preveen-stack]

Is this issue still valid?

[SethTisue]

@preveen-stack it would be helpful if you attempted to verify that yourself. Has kind-projector been modified to follow this advice?:

Compiler plugins need to be adapted to call the overload of warning that takes a Category and a site

If it has been, are there still warnings coming from the plug-in that can't be suppressed, as @neko-kai's comment above seems to indicate? Are you able to reproduce that?