Imported From: https://issues.scala-lang.org/browse/SI-7456?orig=1
Reporter: @paulp
See #7211

@paulp said:
Oh, it's because it checks with equals. That is increasingly a problem for me.

@paulp said:
So actually I guess this is getting better, not worse because this:

class A
final case class B(xs: List[A]) extends A

object Test {
  def f(x: B) = x match { case B(x: A)          => true ; case _ => false }
  def g(x: B) = x match { case B((x: A) :: Nil) => true ; case _ => false }

  def main(args: Array[String]): Unit = {
    println(f(B(new A :: Nil)))
    println(g(B(new A :: Nil)))
  }
}

Compiles with no warning in 2.9, but warns in 2.10. Which I should know, having written the warning.

a.scala:5: warning: fruitless type test: a value of type List[A] cannot also be a A
  def f(x: B) = x match { case B(x: A)          => true ; case _ => false }
                                    ^
one warning found

@retronym said (edited on May 5, 2013 5:24:25 PM UTC):
Akin to #7211. Making A final fails the compile.

@paulp said:
Reopening for me to investigate an -Xlint warning.

as spec'ed. needs SIP