Merge pull request #1615 from retronym/ticket/6648

SI-6648 copyAttrs must preserve TypeTree#wasEmpty

1 files changed, 13 insertions, 0 deletions

diff --git a/src/reflect/scala/reflect/internal/Trees.scala b/src/reflect/scala/reflect/internal/Trees.scala
index 53b40da8f6..b8f5e73acb 100644
--- a/src/reflect/scala/reflect/internal/Trees.scala
+++ b/src/reflect/scala/reflect/internal/Trees.scala
@@ -482,6 +482,10 @@ trait Trees extends api.Trees { self: SymbolTable =>
 
   case class TypeTree() extends TypTree with TypeTreeContextApi {
     private var orig: Tree = null
+    /** Was this type tree originally empty? That is, does it now contain
+      * an inferred type that must be forgotten in `resetAttrs` to
+      * enable retyping.
+      */
     private[scala] var wasEmpty: Boolean = false
 
     override def symbol = typeTreeSymbol(this) // if (tpe == null) null else tpe.typeSymbol
@@ -502,6 +506,15 @@ trait Trees extends api.Trees { self: SymbolTable =>
       wasEmpty = isEmpty
       setType(tp)
     }
+
+    override private[scala] def copyAttrs(tree: Tree) = {
+      super.copyAttrs(tree)
+      tree match {
+        case other: TypeTree => wasEmpty = other.wasEmpty // SI-6648 Critical for correct operation of `resetAttrs`.
+        case _ =>
+      }
+      this
+    }
   }
   object TypeTree extends TypeTreeExtractor