Merge pull request #1871 from tonini/mix-iex-task

Add mix iex that simply fails and tell users to use iex -S mix

Author: José Valim

lib/mix/lib/mix/tasks/iex.ex

@@ -0,0 +1,10 @@
+defmodule Mix.Tasks.Iex do
+  use Mix.Task
+
+  @hidden true
+
+  def run(_) do
+    raise Mix.Error, message: "Cannot start IEx after the VM was booted, " <>
+                              "to use IEx with Mix, please run: iex -S mix"
+  end
+end

lib/mix/test/mix/tasks/iex_test.exs

@@ -0,0 +1,15 @@
+Code.require_file "../../test_helper.exs", __DIR__
+
+defmodule Mix.Tasks.IexTest do
+  use MixTest.Case
+
+  test "iex raises error message about correct usage" do
+    in_fixture "only_mixfile", fn ->
+      error_message = "Cannot start IEx after the VM was booted, " <>
+                      "to use IEx with Mix, please run: iex -S mix"
+      assert_raise Mix.Error, error_message, fn ->
+        Mix.Tasks.Iex.run []
+      end
+    end
+  end
+end