Imported From: https://issues.scala-lang.org/browse/SI-7794?orig=1
Reporter: Martin Zuber (mzuber)
Affected Versions: 2.10.2
Attachments:

• TransformAnnotation.scala (created on Aug 29, 2013 11:25:41 AM UTC, 1284 bytes)

@xeno-by said:
The problem here is that typechecking pattern requires a special typechecker mode called PATTERNmode. In fact, there's a bunch of such modes that cover typechecking types, type constructors, super constructor calls, etc. Unfortunately, c.typeCheck works in EXPRmode and doesn't provide a way to customize it.

There are multiple ways to addressing this problem. The first one involves exposing a number of specialized typeCheckXXX methods, e.g. typeCheckExpr, typeCheckType, typeCheckPattern, etc. The second one implies introducing Mode and passing it as a parameter to c.typeCheck. I don't feel very comfortable with either of them (the first one means a bunch of new methods, the second one means another class in the reflection API), so I would like to defer this decision to the reflection API revamp that is supposedly happening in 2.12.

In the meanwhile, you can cast to internal APIs to work around the problem (please note that PATTERNmode requires a non-wildcard expected type - you can get it by typechecking the scrutinee of the pattern match):

import scala.reflect.macros.Context
import language.experimental.macros

object Macros {
  def impl(c: Context) = {
    import c.universe._
    val expr = q"List(1)"
    val texpr = c.typeCheck(expr)
    val pat = pq"List(1)"
    val tpat = {
      val g = c.universe.asInstanceOf[scala.tools.nsc.Global]
      val ty = c.asInstanceOf[scala.reflect.macros.contexts.Context].callsiteTyper.asInstanceOf[g.analyzer.Typer]
      val tpat = ty.typed(pat.asInstanceOf[g.Tree], scala.reflect.internal.Mode.PATTERNmode, g.typeOf[List[Int]])
      tpat.asInstanceOf[Tree]
    }
    println((texpr, tpat))
    c.literalUnit
  }

  def foo = macro impl
}

object Test extends App {
  println(Macros.foo)
}

12:38 ~/Projects/Master/sandbox (master)$ scalac Macros.scala && scalac Test.scala
(immutable.this.List.apply[Int](1),immutable.this.List.unapplySeq[Int](<unapply-selector>) <unapply> (1))

Would that work for you?

Martin Zuber (mzuber) said:
This will work for me, thank you for the hint.

@xeno-by said:
#6814