Merge pull request #3797 from retronym/topic/exhaust-compound

SI-8631 Treat `A with Sealed` as enumerable for pattern matching

1 files changed, 14 insertions, 4 deletions

diff --git a/src/compiler/scala/tools/nsc/transform/patmat/MatchAnalysis.scala b/src/compiler/scala/tools/nsc/transform/patmat/MatchAnalysis.scala
index 894f959319..e1a663ea41 100644
--- a/src/compiler/scala/tools/nsc/transform/patmat/MatchAnalysis.scala
+++ b/src/compiler/scala/tools/nsc/transform/patmat/MatchAnalysis.scala
@@ -104,11 +104,18 @@ trait TreeAndTypeAnalysis extends Debugging {
         // TODO case _ if tp.isTupleType => // recurse into component types
         case modSym: ModuleClassSymbol =>
           Some(List(tp))
+        case sym: RefinementClassSymbol =>
+          val parentSubtypes: List[Option[List[Type]]] = tp.parents.map(parent => enumerateSubtypes(parent))
+          if (parentSubtypes exists (_.isDefined))
+            // If any of the parents is enumerable, then the refinement type is enumerable.
+            Some(
+              // We must only include subtypes of the parents that conform to `tp`.
+              // See neg/virtpatmat_exhaust_compound.scala for an example.
+              parentSubtypes flatMap (_.getOrElse(Nil)) filter (_ <:< tp)
+            )
+          else None
         // make sure it's not a primitive, else (5: Byte) match { case 5 => ... } sees no Byte
-        case sym if !sym.isSealed || isPrimitiveValueClass(sym) =>
-          debug.patmat("enum unsealed "+ ((tp, sym, sym.isSealed, isPrimitiveValueClass(sym))))
-          None
-        case sym =>
+        case sym if sym.isSealed =>
           val subclasses = debug.patmatResult(s"enum $sym sealed, subclasses")(
             // symbols which are both sealed and abstract need not be covered themselves, because
             // all of their children must be and they cannot otherwise be created.
@@ -136,6 +143,9 @@ trait TreeAndTypeAnalysis extends Debugging {
               else None
             }
           })
+        case sym =>
+          debug.patmat("enum unsealed "+ ((tp, sym, sym.isSealed, isPrimitiveValueClass(sym))))
+          None
       }
 
     // approximate a type to the static type that is fully checkable at run time,