Constrain patterns by both GADT upper bound & upcast

Author: dwijnand

compiler/src/dotty/tools/dotc/core/PatternTypeConstrainer.scala

@@ -143,10 +143,10 @@ trait PatternTypeConstrainer { self: TypeComparer =>
               ctx.gadt.bounds(scrut.symbol) match {
                 case tb: TypeBounds =>
                   val hi = tb.hi
-                  constrainPatternType(pat, hi)
-                case null => false
+                  tryConstrainSimplePatternType(pat, hi)
+                case null => true
               }
-            case _ => false
+            case _ => true
           }
 
           def trySuperType =
@@ -159,7 +159,7 @@ trait PatternTypeConstrainer { self: TypeComparer =>
               tryConstrainSimplePatternType(pat, upcasted) || constrainUpcasted(upcasted)
             else true
 
-          tryGadtBounds || trySuperType
+          tryGadtBounds && trySuperType
       }
     }