SI-4859 Don't elide qualifiers when selecting nested modules.

Otherwise we fail to throw in:

   {???; Predef}.DummyImplicit.dummyImplicit

We still elide the initialization of `Outer` in `Outer.Inner.foo`
as before, although that seems a little dubious to me.

In total, we had to change RefChecks, Flatten, and GenICode
to effect this change. A recently fixed bug in tail call elimination
was also due to assuming that the the qualifier of a Select node
wasn't worthy of traversal.  Let's keep a close eye out for more
instances of this problem.

1 files changed, 8 insertions, 1 deletions

diff --git a/src/compiler/scala/tools/nsc/transform/Flatten.scala b/src/compiler/scala/tools/nsc/transform/Flatten.scala
index 7fe3a5da5c..85516f1995 100644
--- a/src/compiler/scala/tools/nsc/transform/Flatten.scala
+++ b/src/compiler/scala/tools/nsc/transform/Flatten.scala
@@ -12,6 +12,7 @@ import scala.collection.mutable.ListBuffer
 
 abstract class Flatten extends InfoTransform {
   import global._
+  import treeInfo.isExprSafeToInline
 
   /** the following two members override abstract members in Transform */
   val phaseName: String = "flatten"
@@ -117,7 +118,13 @@ abstract class Flatten extends InfoTransform {
           liftedDefs(sym.enclosingTopLevelClass.owner) += tree
           EmptyTree
         case Select(qual, name) if sym.isStaticModule && !sym.isTopLevel =>
-          exitingFlatten(atPos(tree.pos)(gen.mkAttributedRef(sym)))
+          exitingFlatten {
+            atPos(tree.pos) {
+              val ref = gen.mkAttributedRef(sym)
+              if (isExprSafeToInline(qual)) ref
+              else Block(List(qual), ref).setType(tree.tpe) // need to execute the qualifier but refer directly to the lifted module.
+            }
+          }
         case _ =>
           tree
       }