More work on inline classes.

Fail compile if AnyVal is inherited by a trait, a non-@inline
class, or a class with an AnyRef parent somewhere.  Added tests.
Added logging, like

  [log extmethods] Inline class class Bippy spawns extension method.
    Old: def getClass: Class[_ <: Bippy]
    New: final def extension$getClass($this: Bippy): Class[_ <: Bippy]

Fixed what I hope was a bug in ExtensionMethods where the original
method params were dropped.

Since adding a NonNull parent was also inflicting an AnyRef on AnyVal
subclasses, suppressed that for those. Had the bright idea that AnyVal
could extend NotNull. It doesn't seem to accomplish much, but then,
I don't think NotNull accomplishes much. Still, maybe it's time to
restrict the ways one can use AnyVal so one can't do this:

  scala> var x: AnyVal = _
  x: AnyVal = null

1 files changed, 4 insertions, 2 deletions

diff --git a/src/compiler/scala/tools/nsc/typechecker/Namers.scala b/src/compiler/scala/tools/nsc/typechecker/Namers.scala
index b9f3adec75..2f31347829 100644
--- a/src/compiler/scala/tools/nsc/typechecker/Namers.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/Namers.scala
@@ -1407,7 +1407,9 @@ trait Namers extends MethodSynthesis {
       }
 
       if (sym.isClass && sym.hasAnnotation(ScalaInlineClass) && !phase.erasedTypes) {
-        ensureParent(NotNullClass)
+        if (!sym.isSubClass(AnyValClass))
+          ensureParent(NotNullClass)
+
         sym setFlag FINAL
       }
 
@@ -1437,7 +1439,7 @@ trait Namers extends MethodSynthesis {
       checkNoConflict(PRIVATE, PROTECTED)
       // checkNoConflict(PRIVATE, OVERRIDE) // this one leads to bad error messages like #4174, so catch in refchecks
       // checkNoConflict(PRIVATE, FINAL)    // can't do this because FINAL also means compile-time constant
-      checkNoConflict(ABSTRACT, FINAL)
+      // checkNoConflict(ABSTRACT, FINAL)   // this one gives a bad error for non-@inline classes which extend AnyVal
       // @PP: I added this as a sanity check because these flags are supposed to be
       // converted to ABSOVERRIDE before arriving here.
       checkNoConflict(ABSTRACT, OVERRIDE)