Change Space intersect so that the fallback for extractors matches the fallback for type spaces

Author: dwijnand

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

@@ -212,14 +212,14 @@ trait SpaceLogic {
         if (isSubType(tp2, tp1)) b
         else if (canDecompose(tp1)) tryDecompose1(tp1)
         else if (isSubType(tp1, tp2)) a // problematic corner case: inheriting a case class
-        else Empty
+        else intersectUnrelatedAtomicTypes(tp1, tp2)
       case (Prod(tp1, fun, ss), Typ(tp2, _)) =>
         if (isSubType(tp1, tp2)) a
         else if (canDecompose(tp2)) tryDecompose2(tp2)
         else if (isSubType(tp2, tp1)) a  // problematic corner case: inheriting a case class
-        else Empty
+        else intersectUnrelatedAtomicTypes(tp1, tp2)
       case (Prod(tp1, fun1, ss1), Prod(tp2, fun2, ss2)) =>
-        if (!isSameUnapply(fun1, fun2)) Empty
+        if (!isSameUnapply(fun1, fun2)) intersectUnrelatedAtomicTypes(tp1, tp2)
         else if (ss1.zip(ss2).exists(p => simplify(intersect(p._1, p._2)) == Empty)) Empty
         else Prod(tp1, fun1, ss1.zip(ss2).map((intersect _).tupled))
     }

tests/patmat/i12805-fallout.scala

@@ -16,11 +16,15 @@ abstract class Tree[-T >: Untyped] {
   }
 }
 
-case class  Ident[-T >: Untyped]() extends Tree[T]
-case class DefDef[-T >: Untyped]() extends Tree[T]
+case class   Ident[-T >: Untyped]() extends Tree[T]
+case class  DefDef[-T >: Untyped]() extends Tree[T]
+case class Inlined[-T >: Untyped]() extends Tree[T]
+case class CaseDef[-T >: Untyped]() extends Tree[T]
 
 def test[T >: Untyped](tree: Tree[T], tp: Type) = tree.withType(tp) match {
-  case Ident()  => 1
-  case DefDef() => 2
-  case _        => 3
+  case Ident()       => 1
+  case DefDef()      => 2
+  case _: Inlined[_] => 3
+  case CaseDef()     => 4
+  case _             => 5
 }