Follow XDG base dir specification in Mix (#8933)

Author: maennchen

lib/mix/lib/mix/cli.ex

@@ -125,7 +125,7 @@ defmodule Mix.CLI do
   end
 
   defp load_dot_config do
-    path = Path.join(Mix.Utils.mix_home(), "config.exs")
+    path = Path.join(Mix.Utils.mix_config_home(), "config.exs")
 
     if File.regular?(path) do
       Mix.Task.run("loadconfig", [path])

lib/mix/lib/mix/utils.ex

@@ -4,8 +4,8 @@ defmodule Mix.Utils do
   @doc """
   Gets the Mix home.
 
-  It defaults to `~/.mix` unless the `MIX_HOME`
-  environment variable is set.
+  It uses the the locations `MIX_HOME`, `XDG_DATA_HOME/mix`,
+  `~/.mix` with decreasing priority.
 
   Developers should only store entries in the
   `MIX_HOME` directory which are guaranteed to
@@ -15,7 +15,29 @@ defmodule Mix.Utils do
   stored there.
   """
   def mix_home do
-    System.get_env("MIX_HOME") || Path.expand("~/.mix")
+    case {System.get_env("MIX_HOME"), System.get_env("XDG_DATA_HOME")} do
+      {directory, _} when is_binary(directory) -> directory
+      {nil, directory} when is_binary(directory) -> :filename.basedir(:user_data, "mix")
+      {nil, nil} -> Path.expand("~/.mix")
+    end
+  end
+
+  @doc """
+  Gets possible location of global Mix configuration.
+
+  Possible locations:
+
+   * `~/.mix`
+   * `MIX_HOME`
+   * `XDG_CONFIG_HOME/mix`
+
+  """
+  def mix_config_home do
+    case {System.get_env("MIX_HOME"), System.get_env("XDG_CONFIG_HOME")} do
+      {directory, _} when is_binary(directory) -> directory
+      {nil, directory} when is_binary(directory) -> :filename.basedir(:user_config, "mix")
+      {nil, nil} -> Path.expand("~/.mix")
+    end
   end
 
   @doc """

lib/mix/test/mix/utils_test.exs

@@ -7,6 +7,23 @@ defmodule Mix.UtilsTest do
   use MixTest.Case
   doctest Mix.Utils
 
+  setup do
+    # Store state before test
+    mix_home = System.get_env("MIX_HOME")
+
+    # Clear all variables to get a reproducible test
+    System.delete_env("MIX_HOME")
+    System.delete_env("XDG_DATA_HOME")
+    System.delete_env("XDG_CONFIG_HOME")
+
+    # Reset Env Variables
+    on_exit(fn ->
+      System.put_env("MIX_HOME", mix_home)
+      System.delete_env("XDG_DATA_HOME")
+      System.delete_env("XDG_CONFIG_HOME")
+    end)
+  end
+
   test "command to module" do
     assert Mix.Utils.command_to_module("cheers", Mix.Tasks) == {:module, Mix.Tasks.Cheers}
     assert Mix.Utils.command_to_module("unknown", Mix.Tasks) == {:error, :nofile}
@@ -103,6 +120,40 @@ defmodule Mix.UtilsTest do
              Mix.Utils.read_path("http://10.0.0.0/", timeout: 0)
   end
 
+  describe "mix_home/0" do
+    test "prefers MIX_HOME over XDG_DATA_HOME" do
+      System.put_env("MIX_HOME", "mix_home")
+      System.put_env("XDG_DATA_HOME", "xdg_data_home")
+      assert "mix_home" = Mix.Utils.mix_home()
+    end
+
+    test "falls back to XDG_DATA_HOME/mix" do
+      System.put_env("XDG_DATA_HOME", "xdg_data_home")
+      assert :filename.basedir(:user_data, "mix") == Mix.Utils.mix_home()
+    end
+
+    test "falls back to $HOME/.mix" do
+      assert Path.expand("~/.mix") == Mix.Utils.mix_home()
+    end
+  end
+
+  describe "mix_config_home/0" do
+    test "prefers MIX_HOME over XDG_CONFIG_HOME" do
+      System.put_env("MIX_HOME", "mix_home")
+      System.put_env("XDG_CONFIG_HOME", "xdg_data_home")
+      assert "mix_home" = Mix.Utils.mix_config_home()
+    end
+
+    test "falls back to XDG_CONFIG_HOME/mix" do
+      System.put_env("XDG_CONFIG_HOME", "xdg_config_home")
+      assert :filename.basedir(:user_config, "mix") == Mix.Utils.mix_config_home()
+    end
+
+    test "falls back to $HOME/.mix" do
+      assert Path.expand("~/.mix") == Mix.Utils.mix_config_home()
+    end
+  end
+
   defp assert_ebin_symlinked_or_copied(result) do
     case result do
       {:ok, paths} ->

lib/mix/test/test_helper.exs

@@ -185,6 +185,8 @@ end
 home = MixTest.Case.tmp_path(".mix")
 File.mkdir_p!(home)
 System.put_env("MIX_HOME", home)
+System.delete_env("XDG_DATA_HOME")
+System.delete_env("XDG_CONFIG_HOME")
 
 rebar = System.get_env("REBAR") || Path.expand("fixtures/rebar", __DIR__)
 File.cp!(rebar, Path.join(home, "rebar"))