SI-7596 Curtail overloaded symbols during unpickling

In code like:

    object O { val x = A; def x(a: Any) = ... }
    object P extends O.x.A

The unpickler was using an overloaded symbol for `x` in the
parent type of `P`. This led to compilation failures under
separate compilation.

The code that leads to this is in `Unpicklers`:

    def fromName(name: Name) = name.toTermName match {
      case nme.ROOT     => loadingMirror.RootClass
      case nme.ROOTPKG  => loadingMirror.RootPackage
      case _            => adjust(owner.info.decl(name))
    }

This commit filters the overloaded symbol based its stability
unpickling a singleton type. That seemed a slightly safer place
than in `fromName`.

1 files changed, 6 insertions, 0 deletions

diff --git a/test/files/pos/t7596b/B.scala b/test/files/pos/t7596b/B.scala
new file mode 100644
index 0000000000..cbcf149c23
--- /dev/null
+++ b/test/files/pos/t7596b/B.scala
@@ -0,0 +1,6 @@
+class DAOBase[E]{
+  type TableType <: Config.driver.Table[E]
+}
+class SitesDAO extends DAOBase[String]{
+  type TableType = Sites
+}