WIP Fix further examples

Questionable fix.

Author: Blaisorblade

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

@@ -597,7 +597,7 @@ class SpaceEngine(implicit ctx: Context) extends SpaceLogic {
       case tp: RefinedType =>
         recur(tp.parent)
       case tp: TypeRef =>
-        recur(tp.prefix) && !(tp.classSymbol.is(AbstractFinal))
+        (tp.prefix.stripTypeVar == defn.NothingType || recur(tp.prefix)) && !(tp.classSymbol.is(AbstractFinal))
       case _ =>
         true
     }

tests/patmat/i4880a.scala

@@ -0,0 +1,17 @@
+sealed abstract class AbstractFile
+class PlainFile(path: String) extends AbstractFile
+class VirtualFile(name: String) extends AbstractFile
+abstract class ZipArchive(path: String) extends AbstractFile {
+  sealed abstract class Entry(name: String) extends VirtualFile(name)
+  class DirEntry(path: String) extends Entry(path)
+}
+
+object Test {
+  def foo(file: AbstractFile) =  file match {
+    case a: PlainFile =>
+    case b: ZipArchive =>
+    case c1: ZipArchive#Entry =>
+    case c1: ZipArchive#DirEntry =>
+    case c: VirtualFile =>
+  }
+}

tests/patmat/i4880b.scala

@@ -0,0 +1,16 @@
+sealed abstract class AbstractFile
+class PlainFile(path: String) extends AbstractFile
+class VirtualFile(name: String) extends AbstractFile
+abstract class ZipArchive(path: String) extends AbstractFile {
+  sealed abstract class Entry(name: String) extends VirtualFile(name)
+  class DirEntry(path: String) extends Entry(path)
+}
+
+object Test {
+  def foo(file: AbstractFile) =  file match {
+    case a: PlainFile =>
+    case b: ZipArchive =>
+    case c1: ZipArchive#Entry =>
+    case c: VirtualFile =>
+  }
+}