Merge pull request #2257 from dotty-staging/fix-2253

Fix #2253: avoid match exception in case of refinement types

Author: liufengyun

compiler/src/dotty/tools/dotc/transform/patmat/Space.scala

@@ -537,6 +537,7 @@ class SpaceEngine(implicit ctx: Context) extends SpaceLogic {
               tp.refinedName,
               tpb.derivedTypeBounds(follow(lo, false), follow(hi, true))
             )
+          case tp => tp
         }
       case _ => tp
     }

tests/patmat/i2253.scala

@@ -0,0 +1,7 @@
+sealed trait S
+object O extends S
+trait T
+
+class Test {
+  def m(s: S { val x: Int }) = s match { case _: T => ; }
+}