Fix #12559: Try decomposable types in isSubspace

Author: liufengyun

Diff for: compiler/src/dotty/tools/dotc/transform/patmat/Space.scala

@@ -176,6 +176,8 @@ trait SpaceLogic {
         ss.forall(isSubspace(_, b))
       case (Typ(tp1, _), Typ(tp2, _)) =>
         isSubType(tp1, tp2)
+        || canDecompose(tp1) && tryDecompose1(tp1)
+        || canDecompose(tp2) && tryDecompose2(tp2)
       case (Typ(tp1, _), Or(ss)) =>  // optimization: don't go to subtraction too early
         ss.exists(isSubspace(a, _)) || tryDecompose1(tp1)
       case (_, Or(_)) =>

Diff for: tests/patmat/i12559.check

@@ -0,0 +1,2 @@
+10: Match case Unreachable
+27: Match case Unreachable

Diff for: tests/patmat/i12559.scala

@@ -0,0 +1,35 @@
+package akka.event
+
+object TestA:
+  sealed trait LogEvent
+
+  object LogEvent:
+    def myOrdinal(e: LogEvent): Int = e match
+      case e: Error => 0
+      // case e: Warning => 1
+      case e: LogEventWithMarker => 2
+
+
+  class Error() extends LogEvent
+  class Error2() extends Error() with LogEventWithMarker
+
+  // case class Warning() extends LogEvent
+
+  sealed trait LogEventWithMarker extends LogEvent
+
+object TestB:
+  sealed trait LogEvent
+
+  object LogEvent:
+    def myOrdinal(e: LogEvent): Int = e match
+      case e: Error => 0
+      case e: Warning => 1
+      case e: LogEventWithMarker => 2
+
+
+  case class Error() extends LogEvent
+  class Error2() extends Error() with LogEventWithMarker
+
+  case class Warning() extends LogEvent
+
+  sealed trait LogEventWithMarker extends LogEvent