false positive unused warning in for comprehensions

[xuwei-k]

Reproduction steps

Scala 2.13.15, 2.13.16 and 2.13.17-bin-ebdaf73

build.sbt

Global / resolvers += "scala-integration" at "https://scala-ci.typesafe.com/artifactory/scala-integration/"

scalaVersion := "2.13.17-bin-ebdaf73"

scalacOptions += "-Wunused"

Main.scala

case class A(x: Int, y: Int)

object Main {
  for {
    a <- List.empty[A]
    A(x, y) = a
  } yield x + y
}

Problem

[warn] false-positive-unused-warn/Main.scala:6:7: pattern var x in value $anonfun is never used
[warn]     A(x, y) = a
[warn]       ^
[warn] false-positive-unused-warn/Main.scala:6:10: pattern var y in value $anonfun is never used
[warn]     A(x, y) = a
[warn]          ^
[warn] two warnings found

x and y not unused.

[SethTisue]

looks like one @som-snytt will be all over

[som-snytt]

Yes, thanks, although I believe the current idiom is "all under".

Thanks for the report!

[som-snytt]

Ha, this is because it sees that pattern vars in A(x, y) have the "canonical names" in the case class, so it doesn't want to warn about them. However, that means they aren't tracked, so that the artifact valdefs appear unused.