Merge pull request #1971 from rcillo/rd-improve-helpers-r-error-message

Improve error message for IEx.Helpers.r when module does not exist.

Author: José Valim

lib/iex/lib/iex/helpers.ex

@@ -308,6 +308,10 @@ defmodule IEx.Helpers do
   end
 
   defp do_r(module) do
+    unless Code.ensure_loaded?(module) do
+      raise ArgumentError, message: "could not load nor find module: #{inspect module}"
+    end
+
     source = source(module)
     cond do
       source == nil ->

lib/iex/test/iex/helpers_test.exs

@@ -305,7 +305,7 @@ defmodule IEx.HelpersTest do
   end
 
   test "r helper unavailable" do
-    assert_raise UndefinedFunctionError, "undefined function: :non_existent_module.module_info/1", fn ->
+    assert_raise ArgumentError, "could not load nor find module: :non_existent_module", fn ->
       r :non_existent_module
     end
   end