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, 3 deletions

diff --git a/src/compiler/scala/tools/nsc/typechecker/Macros.scala b/src/compiler/scala/tools/nsc/typechecker/Macros.scala
index 4d1ab98fa0..86c59bc671 100644
--- a/src/compiler/scala/tools/nsc/typechecker/Macros.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/Macros.scala
@@ -691,9 +691,11 @@ trait Macros extends scala.tools.reflect.FastTrack with Traces {
 
             var expectedTpe = expandee.tpe
             if (isNullaryInvocation(expandee)) expectedTpe = expectedTpe.finalResultType
-            var typechecked = typecheck("macro def return type", expanded, expectedTpe)
-            typechecked = typecheck("expected type", typechecked, pt)
-            typechecked
+            // also see http://groups.google.com/group/scala-internals/browse_thread/thread/492560d941b315cc
+            val expanded0 = duplicateAndKeepPositions(expanded)
+            val expanded1 = typecheck("macro def return type", expanded0, expectedTpe)
+            val expanded2 = typecheck("expected type", expanded1, pt)
+            expanded2
           } finally {
             popMacroContext()
           }