Can't select correct overloaded method with varargs and Seq

[Arthurm1]

Using Scastie - this compiles on Scala 2.13.2 but not Dotty (0.24.0-RC1)

Minimized code

object Foo {
  val foo = scala.collection.mutable.ArrayBuffer.empty[Seq[Double]]
  val bar = Seq.empty[Double]
  foo.append(bar)
}

Output

cannot merge
  method append in trait Buffer of type (elems: A*): (Buffer.this : scala.collection.mutable.Buffer[A])  and
  method append in trait Buffer of type (elem: A): (Buffer.this : scala.collection.mutable.Buffer[A])
they are both defined in trait Buffer but have matching signatures
  (elems: Seq[Double]*): 
  (Foo.foo : scala.collection.mutable.ArrayBuffer[Seq[Double]]) and
  (elem: Seq[Double]): 
  (Foo.foo : scala.collection.mutable.ArrayBuffer[Seq[Double]])
as members of value foo

Expectation

For Dotty to pick the non-varargs method.

[smarter]

@odersky This looks like a non-trivial limitation of the usage of signatures for overload resolution, the signature of the Buffer#append methods are:

def append(elem: A): this.type
def append(elems: A*): this.type

As seen from a preifx of type ArrayBuffer[Seq[A]] we get:

def append(elem: Seq[A]): this.type
def append(elems: Seq[A]*): this.type

Those have the same signatures, but are otherwise unrelated. It would be good to figure out how to deal with this sooner rather than later since tasty critically relies on signatures for overload resolution.

This is the inverse of the problem detailed in #8929

[odersky]

I'd argue it's the wrong design. Buffer.append should have these signatures:

def append(elem: A): this.type
def append(elem: A, elems: A*): this.type

But it's true we will need to see how we can deal with it.