Disambiguate methods with different return types based on explicitly specified type parameter

[pweisenburger]

The following code compiles using Scala:

object abc {
  trait Test0
  trait Test1 { def apply(f: Int => Int): Unit }

  def v: Test0 = ???
  def v[T]: Test1 = ???

  v[Any] { v => v }
}

Dotty produces the following compiler error:

8 |  v[Any] { v => v }
  |           ^
  |missing parameter type
  |
  |The argument types of an anonymous function must be fully known. (SLS 8.5)
  |Expected type: ?
  |Missing type for parameter v

[nicolasstucki]

Now it fails with

8 |  v[Any] { v => v }
  |  ^
  |  None of the overloaded alternatives of method v in object abc with types
  |   [T] => abc.Test1
  |   => abc.Test0
  |  match type arguments [Any] and arguments (? => ?)

[nicolasstucki]

Now it fails with

  |  v[Any] { v => v }
  |  ^^^^^^
  |  method apply in trait Test1 does not take type parameters

this error is clearer and can easily guide to writing v[Any].apply { v => v } instead.