Do not traverse filesystem on empty paths

See #5551

Signed-off-by: José Valim <jose.valim@plataformatec.com.br>

Author: José Valim

lib/logger/test/logger/utils_test.exs

@@ -100,4 +100,8 @@ defmodule Logger.UtilsTest do
     time = {12, 30, 10, 10}
     assert format_time(time) == ["12", ?:, "30", ?:, "10", ?., [?0, "10"]]
   end
+
+  test "extract_files/2 with empty string returns empty list" do
+    assert extract_files([""], ".ex") == []
+  end
 end

lib/mix/lib/mix/utils.ex

@@ -138,7 +138,11 @@ defmodule Mix.Utils do
 
   def extract_files(paths, pattern) do
     Enum.flat_map(paths, fn path ->
-      if File.regular?(path), do: [path], else: Path.wildcard("#{path}/**/#{pattern}")
+      case :elixir_utils.read_file_type(path) do
+        {:ok, :directory} -> Path.wildcard("#{path}/**/#{pattern}")
+        {:ok, :regular} -> [path]
+        _ -> []
+      end
     end) |> Enum.uniq
   end