Dotty should harder to unify subtypes of sealed traits

[xiaoshihou514]

Consider the following:

sealed trait Expr

case object IntLiteral extends Expr

def foo[A <: Expr](expr: A): A = expr match {
  case IntLiteral => IntLiteral
}

Ouput:

Found:    Playground.IntLiteral.type
Required: A

where:    A is a type in method renameExpr with bounds <: Playground.Expr

This should have compiled since Expr is sealed and every possible branch fulfilled the requirements (returned the same most specific type IntLiteral).

This means that I cannot pass a Foo & Bar into such a type-preserving function (A => A where A <: Foo) and expect the result to unify with Bar.

Thoughts?