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, 2 insertions, 1 deletions

diff --git a/src/compiler/scala/tools/nsc/typechecker/RefChecks.scala b/src/compiler/scala/tools/nsc/typechecker/RefChecks.scala
index c316955a02..b820d8a386 100644
--- a/src/compiler/scala/tools/nsc/typechecker/RefChecks.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/RefChecks.scala
@@ -1389,7 +1389,8 @@ abstract class RefChecks extends InfoTransform with scala.reflect.internal.trans
         case TypeApply(fun, targs) =>
           isClassTypeAccessible(fun)
         case Select(module, apply) =>
-          ( // SI-4859 `CaseClass1().InnerCaseClass2()` must not be rewritten to `new InnerCaseClass2()`
+          ( // SI-4859 `CaseClass1().InnerCaseClass2()` must not be rewritten to `new InnerCaseClass2()`;
+            //          {expr; Outer}.Inner() must not be rewritten to `new Outer.Inner()`.
             treeInfo.isExprSafeToInline(module) &&
             // SI-5626 Classes in refinement types cannot be constructed with `new`. In this case,
             // the companion class is actually not a ClassSymbol, but a reference to an abstract type.