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

1 files changed, 5 insertions, 2 deletions

diff --git a/src/reflect/scala/reflect/internal/Trees.scala b/src/reflect/scala/reflect/internal/Trees.scala
index 9e737528d2..ae9fca14cb 100644
--- a/src/reflect/scala/reflect/internal/Trees.scala
+++ b/src/reflect/scala/reflect/internal/Trees.scala
@@ -1499,15 +1499,18 @@ trait Trees extends api.Trees { self: SymbolTable =>
     }
   }
 
-  private lazy val duplicator = new Transformer {
+  private lazy val duplicator = new Duplicator(focusPositions = true)
+  private class Duplicator(focusPositions: Boolean) extends Transformer {
     override val treeCopy = newStrictTreeCopier
     override def transform(t: Tree) = {
       val t1 = super.transform(t)
-      if ((t1 ne t) && t1.pos.isRange) t1 setPos t.pos.focus
+      if ((t1 ne t) && t1.pos.isRange && focusPositions) t1 setPos t.pos.focus
       t1
     }
   }
 
+  def duplicateAndKeepPositions(tree: Tree) = new Duplicator(focusPositions = false) transform tree
+
   // ------ copiers -------------------------------------------
 
   def copyDefDef(tree: Tree)(