mix: follow XDG base dir specification

[NobbZ]

Environment

• Elixir & Erlang/OTP versions (elixir --version): currently 1.7 and 1.8 (depends on the host) but affects earlier versions as well.
• Operating system: Linux, but maybe affects Mac OS as well

Current behavior

Mix saves it configuration, downloaded data, archives, etc to ~/.mix

Expected behavior

It should follow the XDG Base Dir spec and use appropriate folders from the users configuration to save aforementioned stuff.

This makes it easier for a user to wipe caches, backup config or archives, etc.

This is issue is explicitely about global cache/data/config, not their per-project equivalents.

[josevalim]

Can you please send a proposal to the mailing list? In particular, I would love to hear why we should accept this particular spec, given that it is not 1.0 yet, how it compares to other specs, and who is already adopting it. Thank you. -- *José Valim* www.plataformatec.com.br Skype: jv.ptec Founder and Director of R&D

[NobbZ]

https://groups.google.com/forum/#!topic/elixir-lang-core/7nyDfkgRsI0

[maennchen]

Is the idea here to only change the Mix.Utils.mix_home/1to consider the XDG_DATA_HOME or would a clean implementation also change the location of the following files / folders (those are the ones I found, there may be more):

• archives - ${XDG_DATA_HOME:-/usr/local/share/}mix/archives
• config.exs - ${XDG_CONFIG_HOME:-$HOME/.config/}mix/config.exs
• rebar - ${XDG_DATA_DIRS:-/usr/local/share/}mix/bin/rebar
• rebar3 - ${XDG_DATA_DIRS:-/usr/local/share/}mix/bin/rebar3
• escripts - ${XDG_DATA_HOME:-/usr/local/share/}mix/bin/escripts

[michalmuskala]

When it comes to implementation, the Erlang's filename:basedir/3 function might be of interest, that generally does "the right thing" on each OS.

[maennchen]

If we'd use the directories as specified, this would also change existing file locations for people that do neither specify XDG_* nor MIX_* variables.

Would that be considered a breaking change and has to wait for v2?

[josevalim]

Thanks @maennchen. I took a deeper look at XDG and I have questions:

1. The XDG_CONFIG_HOME does not tell which kind of configuration it is about. For example, is it about manual user configuration or configuration persisted by the software? All examples I have seen online are a bit vague.

2. The _DIRS variables are about data lookups and we don't plan to introduce the complexity behind said lookups.

Unfortunately we can't fallback to filename:basedir/3 because that would be backwards incompatible. :(

[josevalim]

Here is my suggestion:

1. Change Mix.Utils.mix_home/1 to consider XDG_DATA_HOME after MIX_HOME

2. Change whatever loads ~/.mix/config.exs to consider XDG_CONFIG_HOME after MIX_HOME

[maennchen]

@josevalim

The XDG_CONFIG_HOME does not tell which kind of configuration it is about. For example, is it about manual user configuration or configuration persisted by the software? All examples I have seen online are a bit vague.

I experienced the same when I tried to find the correct variable for each directory / file currently inside of MIX_HOME.

Unfortunately we can't fallback to filename:basedir/3 because that would be backwards incompatible. :(

So then this is basically the idea?

diff --git a/lib/mix/lib/mix/utils.ex b/lib/mix/lib/mix/utils.ex
index fd12d1c04..fc63503d9 100644
--- a/lib/mix/lib/mix/utils.ex
+++ b/lib/mix/lib/mix/utils.ex
@@ -15,7 +15,11 @@ 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, _} -> directory
+      {nil, directory} -> Path.join(directory, "mix")
+      {nil, nil} -> Path.expand("~/.mix")
+    end
   end
 
   @doc """

[maennchen]

@josevalim I'll do a PR.