Fail fast if StringIO receives a file operation

Author: josevalim

lib/elixir/lib/string_io.ex

@@ -188,6 +188,12 @@ defmodule StringIO do
     {:noreply, state}
   end
 
+  # Fail fast if someone tries to use it with a File API
+  def handle_info({:file_request, from, reply_as, _req}, state) do
+    send(from, {:file_reply, reply_as, {:error, :enotsup}})
+    {:noreply, state}
+  end
+
   def handle_info({:DOWN, _, _, _, _}, state) do
     {:stop, :shutdown, state}
   end

lib/elixir/test/elixir/string_io_test.exs

@@ -392,4 +392,9 @@ defmodule StringIOTest do
     assert result == {:ok, [{:integer, 1, 1}, {:dot, 1}], 1}
     assert StringIO.contents(pid) == {"", "p>p>"}
   end
+
+  test "returns enotsup for files" do
+    {:ok, pid} = StringIO.open("123")
+    assert :file.position(pid, :cur) == {:error, :enotsup}
+  end
 end