Add documentation for FileFilter

Author: hamzaremmal

compiler/test/dotty/tools/vulpix/FileFilter.scala

@@ -1,26 +1,23 @@
 package dotty.tools.vulpix
 
-sealed trait FileFilter {
+/** FileFilter to accept or reject a file based on its name */
+sealed trait FileFilter:
+  /** Accepts or rejects a file based on the file name  */
   def accept(file: String): Boolean
-}
 
-object FileFilter {
-  def exclude(file: String): FileFilter = exclude(file :: Nil)
+/** Collection of FileFilters to use */
+object FileFilter:
 
-  def exclude(file: String, files: String*): FileFilter =
-    exclude(file :: files.toList)
-
-  def exclude(files: List[String]): FileFilter = new FileFilter {
+  /** FileFilter that rejects the files passed in parameters */
+  def exclude(files: List[String]): FileFilter = new FileFilter:
     private val blackList = files.toSet
     def accept(file: String): Boolean = !blackList.contains(file)
-  }
 
-  def include(files: List[String]): FileFilter = new FileFilter {
+  /** FileFilter that accepts only the files passed in parameters */
+  def include(files: List[String]): FileFilter = new FileFilter:
     private val whiteList = files.toSet
     def accept(file: String): Boolean = whiteList.contains(file)
-  }
 
-  object NoFilter extends FileFilter {
+  /** FileFilter that accepts anytype of files */
+  object NoFilter extends FileFilter:
     def accept(file: String) = true
-  }
-}