Add dot_iex IEx.Config key to take precedence over existing configurations

lib/iex/lib/iex.ex

@@ -321,10 +321,10 @@ defmodule IEx do
 
   ## The .iex.exs file
 
-  When starting, IEx looks for a local `.iex.exs` file (located in the current
-  working directory), then for a global `.iex.exs` file located inside the
-  directory pointed by the `IEX_HOME` environment variable (which defaults
-  to `~`) and loads the first one it finds (if any).
+  When starting, IEx looks for a configured path, then for a local `.iex.exs` file
+  (located in the current working directory), then for a global `.iex.exs` file
+  located inside the directory pointed by the `IEX_HOME` environment variable
+  (which defaults to `~`) and loads the first one it finds (if any).
 
   The code in the chosen `.iex.exs` file is evaluated line by line in the shell's
   context, as if each line were being typed in the shell. For instance, any modules
@@ -356,8 +356,9 @@ defmodule IEx do
       iex(1)> value
       13
 
-  It is possible to load another file by supplying the `--dot-iex` option
-  to IEx. See `iex --help`.
+  It is possible to load another file by configuring the `iex` application's `dot_iex`
+  value (`config :iex, dot_iex: "PATH"` or `IEx.Config.configure(dot_iex: "PATH")`)
+  or supplying the `--dot-iex` option to IEx. See `iex --help`.
 
   In case of remote nodes, the location of the `.iex.exs` files are taken
   relative to the user that started the application, not to the user that
@@ -399,6 +400,7 @@ defmodule IEx do
     * `:alive_prompt`
     * `:alive_continuation_prompt`
     * `:parser`
+    * `:dot_iex`
 
   They are discussed individually in the sections below.
 
@@ -504,6 +506,11 @@ defmodule IEx do
   or `{:incomplete, buffer}`.
 
   If the parser raises, the buffer is reset to an empty string.
+
+  ## dot_iex
+
+  Configure the file loaded into your IEx session when it starts.
+  See more information [in the `.iex.exs` documentation](`m:IEx#module-the-iex-exs-file`).
   """
   @spec configure(keyword()) :: :ok
   def configure(options) do

lib/iex/lib/iex/config.ex

@@ -13,7 +13,8 @@ defmodule IEx.Config do
     :alive_prompt,
     :alive_continuation_prompt,
     :width,
-    :parser
+    :parser,
+    :dot_iex
   ]
 
   # Read API
@@ -88,6 +89,10 @@ defmodule IEx.Config do
     end
   end
 
+  def dot_iex() do
+    Application.get_env(:iex, :dot_iex)
+  end
+
   # Used by default on evaluation cycle
   defp default_color(:eval_interrupt), do: [:yellow]
   defp default_color(:eval_result), do: [:yellow]
@@ -193,6 +198,7 @@ defmodule IEx.Config do
   defp validate_option({:alive_continuation_prompt, new}) when is_binary(new), do: :ok
   defp validate_option({:width, new}) when is_integer(new), do: :ok
   defp validate_option({:parser, tuple}) when tuple_size(tuple) == 3, do: :ok
+  defp validate_option({:dot_iex, path}) when is_binary(path), do: :ok
 
   defp validate_option(option) do
     raise ArgumentError, "invalid configuration #{inspect(option)}"

lib/iex/lib/iex/evaluator.ex

@@ -1,6 +1,8 @@
 defmodule IEx.Evaluator do
   @moduledoc false
 
+  alias IEx.Config
+
   @doc """
   Eval loop for an IEx session. Its responsibilities include:
 
@@ -242,7 +244,9 @@ defmodule IEx.Evaluator do
       ref: ref
     }
 
-    case opts[:dot_iex_path] do
+    dot_iex_path = opts[:dot_iex_path] || Config.dot_iex()
+
+    case dot_iex_path do
       "" -> state
       path -> load_dot_iex(state, path)
     end

lib/iex/test/iex/interaction_test.exs

@@ -277,6 +277,21 @@ defmodule IEx.InteractionTest do
       input = "nested_var\nmy_variable\nmy_fun_nested()"
       assert capture_iex(input, [], dot_iex_path: path) == "42\n13\n:nested"
     end
+
+    @tag :tmp_dir
+    test "configured .iex", %{tmp_dir: tmp_dir} do
+      path =
+        write_dot_iex!(tmp_dir, "configured-dot-iex", """
+        defmodule ConfiguredDotIEx do
+          def my_fun_single, do: :single
+        end
+        import ConfiguredDotIEx
+        my_variable = 42
+        """)
+
+      assert capture_iex("{my_fun_single(), my_variable}", [dot_iex: path], dot_iex_path: nil) ==
+               "{:single, 42}"
+    end
   end
 
   defp write_dot_iex!(tmp_dir, name, contents) do

lib/iex/test/test_helper.exs

@@ -52,13 +52,13 @@ defmodule IEx.Case do
     end
   end
 
-  keys = [:default_prompt, :alive_prompt, :inspect, :colors, :history_size]
-  @iex_env Application.get_all_env(:iex) |> Keyword.take(keys)
+  @keys [:default_prompt, :alive_prompt, :inspect, :colors, :history_size, :dot_iex]
+  @iex_env Application.get_all_env(:iex) |> Keyword.take(@keys)
 
   setup do
     on_exit(fn ->
       env = @iex_env
-      Enum.each(env, fn {k, _} -> Application.delete_env(:iex, k) end)
+      Enum.each(@keys, &Application.delete_env(:iex, &1))
       IEx.configure(env)
     end)