Fixes to BetaReduce and asMemberOf; add a second betaReduce

The new one only reduces straight applications of type lambdas with
definite arguments.  It is called very early on appliedTo, and derivedRefinedType.

The old one, now renamed to normalizeHkApply also handles wildcard arguments
and can garbage collect general unneeded hk-refinements. It is called later, at various
places.

TODO: See what functionality of normalizeHkApply should go into betaReduce instead.
Maybe we can even drop normalizeHkApply? However: need to be careful to maintain aliases
for hk type inference.
Handle LazyRefs in BetaReduce

Needs to be careful to not skip LazyRefs when dealiasing.

- Fix^2 of asMemberOf: This fix ensures that

 - under the old hk scheme test succeeds for compilestdlib and tasty-new-all
 - under the new scheme test succeeds for i94-nada (i.e. REP[T] = T).

- Try to beta-reduce bounds before adding to a constraint.
- More subtle handling of LazyRefs in BetaReduce
- Another refinement to asMemberOf

  Need to assume lastSymbol in sync with lastDenotation.
- Drop isSafe test from BetaReduce

  Instead, track the higherkinded argument names that a
  type variable could potentially instantiate to.

1 files changed, 2 insertions, 0 deletions

diff --git a/src/dotty/tools/dotc/core/ConstraintHandling.scala b/src/dotty/tools/dotc/core/ConstraintHandling.scala
index f8eae186a..3b368ad5e 100644
--- a/src/dotty/tools/dotc/core/ConstraintHandling.scala
+++ b/src/dotty/tools/dotc/core/ConstraintHandling.scala
@@ -285,6 +285,8 @@ trait ConstraintHandling {
           if (!addParamBound(bound)) NoType
           else if (fromBelow) defn.NothingType
           else defn.AnyType
+        case bound: RefinedType =>
+          bound.BetaReduce
         case _ =>
           bound
       }