Type check in macros should not yield an unchecked warning when the corresponding AbsTypeTag is in scope

[scabug]

Type check in macros should not yield an unchecked warning (caused by erasure) when the corresponding AbsTypeTag is in scope:

def test[A, B](a: A, b: B): A = macro test_impl[A,B]

def test_impl[A: c.AbsTypeTag, B](c: Context)(a: c.Expr[A], b: c.Expr[B]): c.Expr[A] = {
    import c.universe._
    reify {
      b.splice match {
        case bb: A => bb 
        case _ => a.splice
      }
    }
  }

Leads to the following compiler warning:

[warn] /home/dk/macropolis/src/main/scala/macropolis/Equalizer.scala:16: abstract type A in type pattern A is unchecked since it is eliminated by erasure
[warn]         case bb:A => bb
[warn]      

Comment by Eugene [1]:

That's a limitation of the typecheck, and I invite you to submit a
bug about it. The thing is that the reifee (the body of the reify
call) is: 1) typechecked and, 2) only then reified. The typechecker
from the step 1 doesn't know anything about reification and, in
particular, doesn't know that T isn't just an abstract type, but is
going to be spliced later.

[1] https://groups.google.com/d/msg/scala-user/alYUId3YmuY/rr9WSuAGjwQJ

[scabug]

Imported From: https://issues.scala-lang.org/browse/SI-6531?orig=1
Reporter: daniel kroeni (dk)
Affected Versions: 2.10.0-M7