Implement NonDescendant

core/src/main/scala/eyrie/ops/package.scala

@@ -2,4 +2,5 @@ package eyrie
 
 package object ops {
   type TrivialDescendant[A] = Descendant[A, A]
+  type NonDescendant[A] = Descendant[A, Nothing]
 }

file/src/main/scala/eyrie/file/instances/FilePathSuccessor.scala

@@ -3,26 +3,31 @@ package eyrie.file.instances
 import java.nio.file.Path
 
 import eyrie.file.FilePath.Internal
-import eyrie.file.{AbsoluteFile, FileName, FilePath, RelativeFile, RootDirectory}
-import eyrie.ops.{Descendant, Successor, TrivialDescendant}
+import eyrie.file.{AbsoluteFile, FileName, FilePath, IdentityFilePath, RelativeFile, RootDirectory}
+import eyrie.ops.{Descendant, NonDescendant, Successor, TrivialDescendant}
 
 private[file]
 trait FilePathSuccessorInstances {
-  implicit def eyrieFileRelativeSuccessorInstance[C]: Successor[
-    RelativeFile[C], FilePath.Relative[C], FileName[C]] =
-    RelativeFilePathSuccessor.asInstanceOf[Successor[RelativeFile[C], FilePath.Relative[C], FileName[C]]]
+  implicit def eyrieFileRelativeDescendantInstance[C]:
+  NonDescendant[RelativeFile[C]] with Successor[RelativeFile[C], FilePath.Relative[C], FileName[C]] =
+    RelativeFilePathDescendant.asInstanceOf[
+      NonDescendant[RelativeFile[C]] with Successor[RelativeFile[C], FilePath.Relative[C], FileName[C]]]
 
-  implicit def eyrieFileAbsoluteDescendantInstance[C]: Successor[
-    AbsoluteFile[C], FilePath.Absolute[C], FileName[C]] with Descendant[AbsoluteFile[C], RootDirectory[C]] =
-    AbsoluteFilePathDescendant.asInstanceOf[Successor[
-      AbsoluteFile[C], FilePath.Absolute[C], FileName[C]] with Descendant[AbsoluteFile[C], RootDirectory[C]]]
+  implicit def eyrieFileAbsoluteDescendantInstance[C]:
+  Descendant[AbsoluteFile[C], RootDirectory[C]] with Successor[AbsoluteFile[C], FilePath.Absolute[C], FileName[C]] =
+    AbsoluteFilePathDescendant.asInstanceOf[
+      Descendant[AbsoluteFile[C], RootDirectory[C]] with Successor[AbsoluteFile[C], FilePath.Absolute[C], FileName[C]]]
 
-  implicit def eyrieFileTrivialDescendantInstance[C]: TrivialDescendant[RootDirectory[C]] =
-    TrivialFilePathDescendant.asInstanceOf[TrivialDescendant[RootDirectory[C]]]
+  implicit def eyrieFileRelativeNonDescendantInstance[C]: NonDescendant[IdentityFilePath[C]] =
+    FilePathNonDescendant.asInstanceOf[NonDescendant[IdentityFilePath[C]]]
+
+  implicit def eyrieFileAbsoluteTrivialDescendantInstance[C]: TrivialDescendant[RootDirectory[C]] =
+    FilePathTrivialDescendant.asInstanceOf[TrivialDescendant[RootDirectory[C]]]
 }
 
 private
-object RelativeFilePathSuccessor extends Successor[RelativeFile[Any], FilePath.Relative[Any], FileName[Any]] {
+object RelativeFilePathDescendant extends NonDescendant[RelativeFile[Any]]
+  with Successor[RelativeFile[Any], FilePath.Relative[Any], FileName[Any]] {
   import eyrie.file.syntax.asJava._
 
   private
@@ -40,11 +45,15 @@ object RelativeFilePathSuccessor extends Successor[RelativeFile[Any], FilePath.R
   override
   def lastSegment: RelativeFile[Any] => FileName[Any] =
     a => Internal.FileName(a.asJava.getFileName)
+
+  override
+  def root: RelativeFile[Any] => Nothing =
+    _ => throw new UnsupportedOperationException("Unexpected invocation")
 }
 
 private
-object AbsoluteFilePathDescendant extends Successor[
-  AbsoluteFile[Any], FilePath.Absolute[Any], FileName[Any]] with Descendant[AbsoluteFile[Any], RootDirectory[Any]] {
+object AbsoluteFilePathDescendant extends Descendant[AbsoluteFile[Any], RootDirectory[Any]]
+  with Successor[AbsoluteFile[Any], FilePath.Absolute[Any], FileName[Any]] {
   import eyrie.file.syntax.asJava._
 
   private
@@ -69,7 +78,14 @@ object AbsoluteFilePathDescendant extends Successor[
 }
 
 private
-object TrivialFilePathDescendant extends TrivialDescendant[RootDirectory[Any]] {
+object FilePathNonDescendant extends NonDescendant[IdentityFilePath[Any]] {
+  override
+  def root: IdentityFilePath[Any] => Nothing =
+    _ => throw new UnsupportedOperationException("Unexpected invocation")
+}
+
+private
+object FilePathTrivialDescendant extends TrivialDescendant[RootDirectory[Any]] {
   override
   def root: RootDirectory[Any] => RootDirectory[Any] =
     identity

file/src/test/scala/eyrie/file/test/DescendantSpec.scala

@@ -4,7 +4,7 @@ import java.nio.file.Paths
 
 import eyrie.file.FilePath.Internal
 import eyrie.file.context.Sys
-import eyrie.file.{AbsoluteFile, FilePath, RootDirectory}
+import eyrie.file.{AbsoluteFile, FilePath, RelativeFile, RootDirectory}
 import org.junit.runner.RunWith
 import org.scalatest.FreeSpec
 import org.scalatest.junit.JUnitRunner
@@ -19,6 +19,9 @@ object DescendantSpec {
 
   val absolute: FilePath.Absolute[Sys] =
     Internal.RootDirectory(Paths.get("a/b/c").toAbsolutePath.getRoot)
+
+  val relativeFile: RelativeFile[Sys] =
+    Internal.RelativeFile(Paths.get("a/b/c"))
 }
 
 @RunWith(classOf[JUnitRunner])
@@ -45,4 +48,13 @@ class DescendantSpec extends FreeSpec {
       absolute.root: RootDirectory[Sys]
     }
   }
+  "RelativeFile" - {
+    "root should not be available" in {
+      illTyped(
+        """
+          relativeFile.root
+        """
+      )
+    }
+  }
 }