Overloading resolution for functions fails with Unit adaptation

[lrytz]

This fails in 2.12 and 2.13

scala> trait SAM { def flup(c: Int): Unit }
scala> object T { def f(x: Int => Unit) = 0; def f(s: SAM) = 1 }

scala> T.f(x => x)
         ^
       error: overloaded method value f with alternatives:
         (s: SAM)Int <and>
         (x: Int => Unit)Int
        cannot be applied to (Int => Int)

scala> T.f(x => {x; ()}) // workaround
res1: Int = 0

Mabye this can be improved. Found by compiling Spark for 2.12 (https://issues.apache.org/jira/browse/SPARK-14220?page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel&focusedCommentId=16540495#comment-16540495)

[adriaanm]

Not related to poor SAMmy per se (but should work for both, ideally):

class C {
  def f(x: Int => Unit) = 0
  def f(x: String => Unit) = 0
  f((x: Int) => x)
}

overloaded method value f with alternatives:
  (x: String => Unit)Int <and>
  (x: Int => Unit)Int
 cannot be applied to (Int => Int)

[paulp]

That wouldn't compile even without the call to f, if it matters. Same erasure.

[adriaanm]

Yep, but here it was mostly intended as minimal way to observe overloading's flailings.