resetAttrs now always erases This.tpe

The symbol of This, if it points to a package class, isn't touched, just
as usual, so that our Select(Select(Select(...))) => This(...) optimization
works fine with attr reset.

However the tpe is now erased, so that subsequent reflective compilation
doesn't spuriously fail when seeing that some subtrees of a tree being
compiled are typed.

Erasing the tpe doesn't pose even a tiniest problem, because, as it can
be seen in typedThis, type is trivially reconstructed from the symbol.

1 files changed, 7 insertions, 4 deletions

diff --git a/src/compiler/scala/tools/nsc/ast/Trees.scala b/src/compiler/scala/tools/nsc/ast/Trees.scala
index 2ad762fd55..f83a9632f6 100644
--- a/src/compiler/scala/tools/nsc/ast/Trees.scala
+++ b/src/compiler/scala/tools/nsc/ast/Trees.scala
@@ -335,14 +335,17 @@ trait Trees extends scala.reflect.internal.Trees { self: Global =>
                 else tree
               case TypeApply(fn, args) if args map transform exists (_.isEmpty) =>
                 transform(fn)
-              case This(_) if tree.symbol != null && tree.symbol.isPackageClass =>
-                tree
               case EmptyTree =>
                 tree
               case _ =>
                 val dupl = tree.duplicate
-                if (tree.hasSymbol && (!localOnly || (locals contains tree.symbol)) && !(keepLabels && tree.symbol.isLabel))
-                  dupl.symbol = NoSymbol
+                if (dupl.hasSymbol) {
+                  val sym = dupl.symbol
+                  val vetoScope = localOnly && !(locals contains sym)
+                  val vetoLabel = keepLabels && sym.isLabel
+                  val vetoThis = dupl.isInstanceOf[This] && sym.isPackageClass
+                  if (!(vetoScope || vetoLabel || vetoThis)) dupl.symbol = NoSymbol
+                }
                 dupl.tpe = null
                 dupl
             }