"macro implementation reference has wrong shape" in the Scala Documentation examples - scala

Question

The following macro is pasted from http://docs.scala-lang.org/overviews/quasiquotes/usecases.html:
import reflect.macros.Context
import language.experimental.macros
val universe = reflect.runtime.universe; import universe._
import reflect.runtime.currentMirror
import tools.reflect.ToolBox
val toolbox = currentMirror.mkToolBox()
object debug {
def apply[T](x: =>T): T = macro impl
def impl(c: Context)(x: c.Tree) = { import c.universe._
val q"..$stats" = x
val loggedStats = stats.flatMap { stat =>
val msg = "executing " + showCode(stat)
List(q"println($msg)", stat)
}
q"..$loggedStats"
}
}
It produces this error message in Scala 2.11.1:
Q.scala:9: error: macro implementation reference has wrong shape. required:
macro [<static object>].<method name>[[<type args>]] or
macro [<macro bundle>].<method name>[[<type args>]]
def apply[T](x: =>T): T = macro impl
^
I've tried varying the code in numerous ways (import reflect.macros.whitebox.Context, import reflect.macros.blackbox.Context, putting scala. at the start of each import, making the arguments consistently by-name or consistently by-value, macro impl[T], getting rid of the type parameter, macro debug.impl, putting the apply after the impl, and more) with no success. What am I doing wrong? Is it something in the imports? Those come (mostly) from a different web page, http://docs.scala-lang.org/overviews/quasiquotes/setup.html.
The same error occurs on both of the other example macros from that page:
object Macro {
def apply(x: Int): Int = macro impl
def impl(c: Context)(x: c.Expr[Int]): c.Expr[Int] = { import c.universe._
c.Expr(q"$x + 1")
}
}
object Macro {
def apply(x: Int): Int = macro impl
def impl(c: Context)(x: c.Tree) = { import c.universe._
q"$x + 1"
}
}

Answer 1

scala Foo.scala wraps the code that you feed to it in an anonymous class. As a result, something like:
import scala.reflect.macros.Context
import scala.language.experimental.macros
object debug {
def apply[T](x: T): T = macro impl
def impl(c: Context)(x: c.Tree): c.Tree = ???
}
Gets transformed into:
[[syntax trees at end of parser]] // Test.scala
package <empty> {
object Main extends scala.AnyRef {
def <init>() = {
super.<init>();
()
};
def main(args: Array[String]): scala.Unit = {
final class $anon extends scala.AnyRef {
def <init>() = {
super.<init>();
()
};
import scala.reflect.macros.Context;
import scala.language.experimental.macros;
object debug extends scala.AnyRef {
def <init>() = {
super.<init>();
()
};
<macro> def apply[T](x: T): T = impl;
def impl(c: Context)(x: c.Tree): c.Tree = $qmark$qmark$qmark
}
};
new $anon()
}
}
}
However, macro implementations must be defined in static object or bundles, which is what the error messages tries to say:
/Users/xeno_by/Projects/211x/sandbox/Test.scala:5: error: macro implementation reference has wrong shape. required:
macro [<static object>].<method name>[[<type args>]] or
macro [<macro bundle>].<method name>[[<type args>]]
def apply[T](x: T): T = macro impl
^
one error found
Unfortunately, if something is put into inside an anonymous class, it's no longer static, which means that scala Foo.scala-style development is incompatible with macros. Consider using alternatives, e.g. scalac or sbt.