Overloading Resolution + Vararg methods: example should be ambiguous

[scabug]

Related to #4728. This compiles, the second alternative is chosen

object t {
  def f(x: Object) = 1
  def f(x: String*) = 2
}
t.f("") // returns 2, should be ambiguous.

According to #4728, it should be ambiguous. I assume the compiler thinks that String* conforms to Object. Maybe because it tests if Seq[String] conforms to Object, not sure.

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Imported From: https://issues.scala-lang.org/browse/SI-8344?orig=1
Reporter: @lrytz
Affected Versions: 2.11.0
See #4728

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@som-snytt said:
I think #8342 will say that autotupling makes the first f applicable to arbitrary strings. There's an issue somewhere with the example with a type parameter.

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@lrytz said:
Right, I forgot about that. Auto-tupling seems just wrong in too many situations.

scala> def f(x: Object) = 0
f: (x: Object)Int

scala> f(1,2,3)
res0: Int = 0

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@som-snytt said:
Is this open because it's still unambiguous under -Yno-adapted-args? If that should matter? Asking for a friend.

apm@mara:~$ goof -Yno-adapted-args
Welcome to Scala version 2.11.0 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0).
Type in expressions to have them evaluated.
Type :help for more information.

scala> object t {
     |   def f(x: Object) = 1
     |   def f(x: String*) = 2
     | }
defined object t

scala> t.f("")
res0: Int = 2

scala> def g[A](a: A) = 7
g: [A](a: A)Int

scala> g(1,2,3)
<console>:9: warning: No automatic adaptation here: use explicit parentheses.
        signature: g[A](a: A): Int
  given arguments: 1, 2, 3
 after adaptation: g((1, 2, 3): (Int, Int, Int))
              g(1,2,3)
               ^
res1: Int = 7

[adriaanm]

Weird, I guess this should be ambiguous. You can't apply a String* to a method expecting an Object, and you can't supply an Object when expecting one or more String (note that, as a formal, the vararg is expanded, while it it's when an argument. -- see #7680).

[adriaanm]

While deciding which one is more specific, you get the following calls to isCompatibleArgs:

isCompatibleArgs false List(Object) <:< List(String)
isCompatibleArgs true List(String*) <:< List(Object)

the second one should be false too