Fix for SI-6662, macro failing too early.

Don't give up before you try tupling. Who knows what
someone might be doing with a Unit.

src/compiler/scala/tools/nsc/typechecker/Typers.scala

@@ -3078,7 +3078,7 @@ trait Typers extends Modes with Adaptations with Tags {
 
             def checkNotMacro() = {
               if (fun.symbol != null && fun.symbol.filter(sym => sym != null && sym.isTermMacro && !sym.isErroneous) != NoSymbol)
-                duplErrorTree(NamedAndDefaultArgumentsNotSupportedForMacros(tree, fun))
+                tryTupleApply getOrElse duplErrorTree(NamedAndDefaultArgumentsNotSupportedForMacros(tree, fun))
             }
 
             if (mt.isErroneous) duplErrTree

test/files/run/t6662.check

@@ -0,0 +1 @@
+()

test/files/run/t6662/Macro_1.scala

@@ -0,0 +1,8 @@
+import language.experimental.macros
+import scala.reflect.macros.Context
+
+object Demo {
+  def id[T](a: T): T = macro idImpl[T]
+
+  def idImpl[T: c.WeakTypeTag](c: Context)(a: c.Expr[T]): c.Expr[T] = a
+}

test/files/run/t6662/Test_2.scala

@@ -0,0 +1,8 @@
+// Macro usage:
+
+object Test {
+   def main(args: Array[String]) {
+      val s = Demo id ()
+      println(s)
+   }
+}