extension method error should account for access modifier

[soronpo]

Compiler version

v3.0.0

Minimized code

class Value[T <: Int](val value: T)

sealed trait DFType:
  type Width <: Int
  val width: Value[Width]

object DFType:
  trait TC[T]:
    type Type <: DFType
    def apply(t: T): Type
  type Aux[T, Type0 <: DFType] = TC[T] { type Type = Type0 }
  transparent inline given ofDFType[T <: DFType]: TC[T] =
    new TC[T]:
      type Type = T
      def apply(t: T): Type = t

  extension [T, Type <: DFType](t: T)(using tc: Aux[T, Type])
    protected def getDFType: Type = tc(t)

final case class DFBits[W <: Int](width: Value[W]) extends DFType:
  type Width = W

val w: Value[8] = DFBits(Value[8](8)).getDFType.width 

Output

[error]    |  val w: Value[8] = DFBits(Value[8](8)).getDFType.width
[error]    |                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[error]    |                    value getDFType is not a member of DFBits[(8 : Int)].
[error]    |                    An extension method was tried, but could not be fully constructed:
[error]    |
[error]    |                        DFType.getDFType(DFiant.core.Minimized.DFBits.apply[(8 : Int)](new Value[8.type](8)))

Expectation

The message "An extension method was tried, but could not be fully constructed" is confusing. The message should clearly indicate that the failure is due to the protected modifier.