macro expansions are now auto-duplicated

The fix still requires macro developers to be careful about sharing trees
by references, because attributed DefTrees will still bring trouble.

However this is an improvement, because it doesn't make matters worse
and automatically fixes situations similar to one in the test.

A much more thorough discussion with a number of open questions left:
http://groups.google.com/group/scala-internals/browse_thread/thread/492560d941b315cc

2 files changed, 35 insertions, 0 deletions

diff --git a/test/files/run/macro-duplicate/Impls_Macros_1.scala b/test/files/run/macro-duplicate/Impls_Macros_1.scala
new file mode 100644
index 0000000000..de81923330
--- /dev/null
+++ b/test/files/run/macro-duplicate/Impls_Macros_1.scala
@@ -0,0 +1,29 @@
+import scala.reflect.macros.Context
+
+object Macros {
+  def impl(c: Context) = {
+    import c.universe._
+    val Expr(Block((cdef: ClassDef) :: Nil, _)) = reify { class C { def x = 2 } }
+    val cdef1 =
+      new Transformer {
+        override def transform(tree: Tree): Tree = tree match {
+          case Template(_, _, ctor :: defs) =>
+            val defs1 = defs collect {
+              case ddef @ DefDef(mods, name, tparams, vparamss, tpt, body) =>
+                val future = Select(Select(Select(Ident(newTermName("scala")), newTermName("concurrent")), newTermName("package")), newTermName("future"))
+                val Future = Select(Select(Ident(newTermName("scala")), newTermName("concurrent")), newTypeName("Future"))
+                val tpt1 = if (tpt.isEmpty) tpt else AppliedTypeTree(Future, List(tpt))
+                val body1 = Apply(future, List(body))
+                val name1 = newTermName("async" + name.toString.capitalize)
+                DefDef(mods, name1, tparams, vparamss, tpt1, body1)
+            }
+            Template(Nil, emptyValDef, ctor +: defs ::: defs1)
+          case _ =>
+            super.transform(tree)
+        }
+      } transform cdef
+    c.Expr[Unit](Block(cdef1 :: Nil, Literal(Constant(()))))
+  }
+
+  def foo = macro impl
+}
\ No newline at end of file
diff --git a/test/files/run/macro-duplicate/Test_2.scala b/test/files/run/macro-duplicate/Test_2.scala
new file mode 100644
index 0000000000..6dbd4382d3
--- /dev/null
+++ b/test/files/run/macro-duplicate/Test_2.scala
@@ -0,0 +1,6 @@
+import scala.concurrent._
+import ExecutionContext.Implicits.global
+
+object Test extends App {
+  Macros.foo
+}
\ No newline at end of file