Overloaded methods in structural types cannot be called

[Duhemm]

import scala.reflect.Selectable.reflectiveSelectable

object O {

  class A
  class B

  type X = {
    def foo(x: A): Unit
    def foo(x: B): Unit
  }

  def bar(x: X): Unit = x.foo(new A)
}

scalac (after commenting out the import):

$ scalac Bar.scala       
warning: there was one feature warning; re-run with -feature for details
one warning found

dotc:

sbt:dotty> dotc Bar.scala
-- Error: Bar.scala:13:26 ------------------------------------------------------
13 |  def bar(x: X): Unit = x.foo(new A)                                        
   |                        ^^^^^                                               
   | none of the overloaded alternatives of method (x: O.A): Unit with types    
   |  (x: O.A): Unit                                                            
   |  (x: O.B): Unit                                                            
   | match arguments (O.A)                                                      
one error found                                                                 

The error goes away if we remove def foo(x: B): Unit from the structural type.

[odersky]

We currently don't support overloads in structural types. So we need to either fix this (which looks hard) or reject the program with an error message at the definition site. I have a tendency to do the second, because it's much easier than the first.