Single abstract method (SAM) composes poorly with Product type

[tribbloid]

Compiler version

3.5.1

Minimized code

In the following code, e1, e2, e3 should be equivalent

object ProductSAM {

  trait Example extends Product {

    def apply(v: Int): String

    override def canEqual(that: Any): Boolean = that.isInstanceOf[Example]

  }

  object e0 extends Example {
    override def apply(v: Int): String = v.toString
  }

  val e1: Example = new Example {
    override def apply(v: Int): String = v.toString
  }

  val e2: Example = { (v: Int) =>
    v.toString
  }
}

Output

e3 is the only definition that triggered the following error:

Found:    Int => String
Required: com.tribbloids.spike.dotty.ProductSAM.Example

Explanation
===========

Tree: {
  def $anonfun(v: Int): String =
    {
      v.toString()
    }
  closure($anonfun)
}
I tried to show that
  Int => String
conforms to
  com.tribbloids.spike.dotty.ProductSAM.Example
but none of the attempts shown below succeeded:

  ==> Int => String  <:  com.tribbloids.spike.dotty.ProductSAM.Example class dotty.tools.dotc.core.Types$CachedAppliedType class dotty.tools.dotc.core.Types$CachedTypeRef  = false

The tests were made under the empty constraint

  val e2: Example = { (v: Int) =>

Expectation

the definition of e3 should work with both Scala 2/3 syntax (right now it breaks in both)