search for implicit conversions should continue after single abstract method conversion failed

[tribbloid]

Compiler version

3.6.2

Minimized code

The following code attempts to unify DepFn (in shapeless 2) with Function1 (in standard library)

the bound type Out cannot be used directly in covariant position unless fully defined (with upper & lower bound), this is a much harder problem which IS NOT in the scope of this ticket. However, this is avoided in the implicit given fn2DepFn[I, O], which fully defined type Out.

object FnAsDepFn {

  trait DepFnK[-I] extends Function1[I, ?] {

    type Out

    def apply(v: I): Out
  }

  trait DepFn[-I, +O] extends Function1[I, O] with DepFnK[I] {
    type Out <: O
  }

  given fn2DepFn[I, O]: Conversion[(I => O), DepFn[I, O]] = {
    new Conversion[(I => O), DepFn[I, O]] {

      def apply(v1: I => O): DepFn[I, O] = {
        new DepFn[I, O] {
          type Out = O
          def apply(v: I): O = v1(v)
        }
      }
    }
  }

  val fnGround: DepFn[Int, String] = fn2DepFn { v =>
    "" + v
  }

  val fn1: DepFn[Int, String] = { v =>
    "" + v
  }

  val fn2: DepFn[Int, String] = { (v: Int) =>
    " " + v
  }

  val fn3: DepFn[?, ?] = { (v: Int) =>
    " " + v
  }
}

Output

/home/peng/git/dottyspike/core/src/main/scala/com/tribbloids/spike/dotty/FnAsDepFn.scala:33:5
Found:    String
Required: com.tribbloids.spike.dotty.FnAsDepFn.DepFn[Int, String]#Out

Explanation
===========

Tree: "".+(v)
I tried to show that
  String
conforms to
  com.tribbloids.spike.dotty.FnAsDepFn.DepFn[Int, String]#Out
but none of the attempts shown below succeeded:

  ==> String  <:  com.tribbloids.spike.dotty.FnAsDepFn.DepFn[Int, String]#Out CachedTypeRef CachedTypeRef  = false

The tests were made under the empty constraint

    "" + v

/home/peng/git/dottyspike/core/src/main/scala/com/tribbloids/spike/dotty/FnAsDepFn.scala:37:5
Found:    String
Required: com.tribbloids.spike.dotty.FnAsDepFn.DepFn[Int, String]#Out

Explanation
===========

Tree: " ".+(v)
I tried to show that
  String
conforms to
  com.tribbloids.spike.dotty.FnAsDepFn.DepFn[Int, String]#Out
but none of the attempts shown below succeeded:

  ==> String  <:  com.tribbloids.spike.dotty.FnAsDepFn.DepFn[Int, String]#Out CachedTypeRef CachedTypeRef  = false

The tests were made under the empty constraint

    " " + v

/home/peng/git/dottyspike/core/src/main/scala/com/tribbloids/spike/dotty/FnAsDepFn.scala:41:5
Found:    String
Required: com.tribbloids.spike.dotty.FnAsDepFn.DepFn[Any, Any]#Out

Explanation
===========

Tree: " ".+(v)
I tried to show that
  String
conforms to
  com.tribbloids.spike.dotty.FnAsDepFn.DepFn[Any, Any]#Out
but none of the attempts shown below succeeded:

  ==> String  <:  com.tribbloids.spike.dotty.FnAsDepFn.DepFn[Any, Any]#Out CachedTypeRef CachedTypeRef  = false

The tests were made under the empty constraint

    " " + v

Expectation

The underdefined type Out problem should be circumvented if the given can be used, instead, it was ignored after SAM rewriting is attempted with an underdefined type Out