import scala.reflect.macros.whitebox._
import scala.language.experimental.macros

class Macros(val c: Context) {
  def impl(x: c.Tree) = ???
}

object Macros {
  def impl(c: Context) = ???
}

object Test extends App {
  def foo: Unit = macro Macros.impl
}

22:24 ~/Projects/Master/sandbox (master)$ s
Test.scala:13: error: macro implementation has incompatible shape:
 required: : Macros.this.c.Expr[Unit]
 or      : : Macros.this.c.Tree
 found   : (x: Macros.this.c.Tree): Nothing
number of parameter sections differ
  def foo: Unit = macro Macros.impl
                               ^
one error found