Pattern-match under "-source future" requires Matchable to check an identical type

[Odomontois]

Compiler version

3.2.2

Minimized code

def collectKeys[A, B, C](xs: Map[A, B])(f: PartialFunction[A, C]): Map[C, B] = 
	xs.collect{ case (f(c) , b) => (c, b) }

Output

With no flags produces no warnings.
With scalacOptions ++= Vector("-source", "future") produces warning

pattern selector should be an instance of Matchable,,
but it has unmatchable type A instead

[kyri-petrou]

I believe this is a similar issue. Minimized code:

final case class Foo(foo: String):
  override def canEqual(that: Any): Boolean = that match
    case f: Foo => ???
    case _      => ???

produces the following warning:

pattern selector should be an instance of Matchable, but it has unmatchable type Any instead

This effectively makes the example on multiversal equality at the bottom of the page produce a warning

[ritschwumm]

@kyri-petrou https://docs.scala-lang.org/scala3/reference/other-new-features/matchable.html# explains what to do for universal equality (but does not mention the asMatchable extension method which might be better than using .asInstanceOf[Matchable])

[bishabosha]

I believe this is a similar issue. Minimized code:

final case class Foo(foo: String):
  override def canEqual(that: Any): Boolean = that match
    case f: Foo => ???
    case _      => ???

This is a different case because here we are type testing if Any is a Foo, which breaks the assumption of the type not opting-into pattern matching. in the OP, A is already known to be A so even though A is not bound by Matchable, the match is not uncovering new information with a type test.