Why does the class body affect implicit resolution?

Question

I accidentally stumbled upon this problem when I was experimenting with abstract classes. The following code:

import shapeless._
class A 
  [tuple <: Product, hlist <: HList]
  (tuple: tuple)
  (implicit tupleGeneric: Generic.Aux[tuple, hlist]) 
{
  private val hlist = tupleGeneric.to(tuple)
  println(hlist)
}
new A((1, 'b')) {}

will not compile with the following message:

could not find implicit value for parameter tupleGeneric: shapeless.Generic.Aux[(Int, Char),shapeless.::[Int,shapeless.::[Char,shapeless.HNil]]]
new A((1, 'b')) {}
    ^

However, if I simply remove the part {}from new A((1, 'b')) {}, it will find that it is implicitly without problems.

Is this a Scala bug or am I missing something?

Answer 1

It turns out that this is a recognized mistake.

https://issues.scala-lang.org/browse/SI-8104