Merge pull request #4083 from retronym/ticket/8947

SI-8947 Avoid cross talk between tag materializers and reify

3 files changed, 10 insertions, 3 deletions

diff --git a/src/compiler/scala/reflect/reify/Taggers.scala b/src/compiler/scala/reflect/reify/Taggers.scala
index 093c2bee22..0863ee38f9 100644
--- a/src/compiler/scala/reflect/reify/Taggers.scala
+++ b/src/compiler/scala/reflect/reify/Taggers.scala
@@ -79,8 +79,7 @@ abstract class Taggers {
     try materializer
     catch {
       case ReificationException(pos, msg) =>
-        c.error(pos.asInstanceOf[c.Position], msg) // this cast is a very small price for the sanity of exception handling
-        EmptyTree
+        c.abort(pos.asInstanceOf[c.Position], msg) // this cast is a very small price for the sanity of exception handling
       case UnexpectedReificationException(pos, err, cause) if cause != null =>
         throw cause
     }
diff --git a/src/compiler/scala/tools/nsc/typechecker/StdAttachments.scala b/src/compiler/scala/tools/nsc/typechecker/StdAttachments.scala
index 57f27a05fd..ea44b9dc39 100644
--- a/src/compiler/scala/tools/nsc/typechecker/StdAttachments.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/StdAttachments.scala
@@ -61,7 +61,7 @@ trait StdAttachments {
     val metadata = MacroExpansionAttachment(expandee, expanded)
     expandee updateAttachment metadata
     expanded match {
-      case expanded: Tree => expanded updateAttachment metadata
+      case expanded: Tree if !expanded.isEmpty => expanded updateAttachment metadata
       case _ => // do nothing
     }
   }
diff --git a/src/reflect/scala/reflect/internal/Trees.scala b/src/reflect/scala/reflect/internal/Trees.scala
index 2f07cef315..35de3adff6 100644
--- a/src/reflect/scala/reflect/internal/Trees.scala
+++ b/src/reflect/scala/reflect/internal/Trees.scala
@@ -9,6 +9,7 @@ package internal
 
 import Flags._
 import scala.collection.{ mutable, immutable }
+import scala.reflect.macros.Attachments
 import util.Statistics
 
 trait Trees extends api.Trees {
@@ -1074,6 +1075,13 @@ trait Trees extends api.Trees {
     override def setType(t: Type) = { requireLegal(t, NoType, "tpe"); this }
     override def tpe_=(t: Type) = setType(t)
 
+    // We silently ignore attempts to add attachments to `EmptyTree`. See SI-8947 for an
+    // example of a bug in macro expansion that this solves.
+    override def setAttachments(attachments: Attachments {type Pos = Position}): this.type = attachmentWarning()
+    override def updateAttachment[T: ClassTag](attachment: T): this.type = attachmentWarning()
+    override def removeAttachment[T: ClassTag]: this.type = attachmentWarning()
+    private def attachmentWarning(): this.type = {devWarning(s"Attempt to mutate attachments on $self ignored"); this}
+
     private def requireLegal(value: Any, allowed: Any, what: String) = (
       if (value != allowed) {
         log(s"can't set $what for $self to value other than $allowed")