Fix File.cp_r/3 in case of a file coping to itself

Author: lexmag

lib/elixir/lib/file.ex

@@ -536,7 +536,7 @@ defmodule File do
 
   """
   @spec cp_r(Path.t, Path.t, (Path.t, Path.t -> boolean)) :: {:ok, [binary]} | {:error, posix, binary}
-  def cp_r(source, destination, callback \\ fn(_, _) -> true end) when is_function(callback) do
+  def cp_r(source, destination, callback \\ &path_differs?/2) when is_function(callback) do
     source = IO.chardata_to_string(source)
     destination = IO.chardata_to_string(destination)
 
@@ -551,7 +551,7 @@ defmodule File do
   Returns the list of copied files otherwise.
   """
   @spec cp_r!(Path.t, Path.t, (Path.t, Path.t -> boolean)) :: [binary] | no_return
-  def cp_r!(source, destination, callback \\ fn(_, _) -> true end) do
+  def cp_r!(source, destination, callback \\ &path_differs?/2) do
     case cp_r(source, destination, callback) do
       {:ok, files} -> files
       {:error, reason, file} ->

lib/elixir/test/elixir/file_test.exs

@@ -129,14 +129,15 @@ defmodule FileTest do
       end
     end
 
-    test :cp_file_to_itself do
+    test :copy_file_to_itself do
       src = dest = tmp_path("tmp.file")
 
       File.write!(src, "here")
 
       try do
         assert File.cp(src, dest) == :ok
         assert File.read!(dest) == "here"
+        assert File.cp_r(src, dest) == {:ok, []}
       after
         File.rm(dest)
       end