Preserve directory permissions in File.cp_r/3 (#15155)

The documentation states that `cp_r/3` maintains "modes" when copying, but
directory permissions were not being preserved - only file permissions.

Author: pnezis

lib/elixir/lib/file.ex

@@ -1277,18 +1277,24 @@ defmodule File do
           {:ok, files} ->
             case mkdir(dest) do
               success when success in [:ok, {:error, :eexist}] ->
-                Enum.reduce_while(files, [dest | acc], fn x, acc ->
-                  case do_cp_r(
-                         Path.join(src, x),
-                         Path.join(dest, x),
-                         on_conflict,
-                         dereference,
-                         acc
-                       ) do
-                    {:error, _, _} = error -> {:halt, error}
-                    acc -> {:cont, acc}
-                  end
-                end)
+                case copy_file_mode(src, dest) do
+                  :ok ->
+                    Enum.reduce_while(files, [dest | acc], fn x, acc ->
+                      case do_cp_r(
+                             Path.join(src, x),
+                             Path.join(dest, x),
+                             on_conflict,
+                             dereference,
+                             acc
+                           ) do
+                        {:error, _, _} = error -> {:halt, error}
+                        acc -> {:cont, acc}
+                      end
+                    end)
+
+                  {:error, reason} ->
+                    {:error, reason, src}
+                end
 
               {:error, reason} ->
                 {:error, reason, dest}

lib/elixir/test/elixir/file_test.exs

@@ -869,6 +869,26 @@ defmodule FileTest do
       assert src_mode == dest_mode
     end
 
+    test "cp_r preserves directory mode" do
+      src = tmp_path("tmp/src_dir")
+      dest = tmp_path("tmp/dest_dir")
+      inner = Path.join(src, "inner")
+
+      File.mkdir_p!(inner)
+      File.chmod!(inner, 0o700)
+
+      try do
+        File.cp_r!(src, dest)
+
+        %File.Stat{mode: src_mode} = File.stat!(inner)
+        %File.Stat{mode: dest_mode} = File.stat!(Path.join(dest, "inner"))
+        assert src_mode == dest_mode
+      after
+        File.rm_rf!(src)
+        File.rm_rf!(dest)
+      end
+    end
+
     @tag :unix
     test "cp_r skips sockets and other special files" do
       # We use tmpdir because macOS has a limit on socket paths