Support MIX_PATH as alternative load paths, closes #889

Author: José Valim

lib/mix/lib/mix/cli.ex

@@ -50,6 +50,7 @@ defmodule Mix.CLI do
 
   defp proceed(args) do
     Mix.Local.append_tasks
+    Mix.Local.append_paths
 
     args = load_mixfile(args)
     { task, args } = get_task(args)

lib/mix/lib/mix/local.ex

@@ -17,6 +17,13 @@ defmodule Mix.Local do
     Code.append_path tasks_path
   end
 
+  @doc """
+  Append mix paths into Erlang code path.
+  """
+  def append_paths do
+    Enum.each Mix.Utils.mix_path, Code.append_path(&1)
+  end
+
   @doc """
   Returns all tasks modules in .mix/tasks.
   """

lib/mix/lib/mix/utils.ex

@@ -22,6 +22,27 @@ defmodule Mix.Utils do
     System.get_env("MIX_HOME") || Path.expand("~/.mix")
   end
 
+  @doc """
+  Gets all extra paths defined in the environment variable
+  MIX_PATH. MIX_PATH may contain multiple paths. If on windows,
+  those paths should be separated by `;`, if on unix systems,
+  use `:`.
+  """
+  def mix_path do
+    if path = System.get_env("MIX_PATH") do
+      String.split(path, path_separator)
+    else
+      []
+    end
+  end
+
+  defp path_separator do
+    case :os.type do
+      { :win32, _ } -> ";"
+      { :unix, _ }  -> ":"
+    end
+  end
+
   @doc """
   Gets the source location of a module as a binary.
   """

lib/mix/test/mix/tasks/local_test.exs

@@ -25,4 +25,17 @@ defmodule Mix.Tasks.LocalTest do
     Mix.Tasks.Local.Uninstall.run ["local.sample"]
     refute File.regular? tmp_path("userhome/.mix/tasks/Elixir-Mix-Tasks-Local-Sample.beam")
   end
+
+  test "manage mix paths" do
+    File.rm_rf! tmp_path("userhome")
+    System.put_env "MIX_PATH", tmp_path("userhome/.mix")
+
+    # Install on MIX_PATH manually
+    File.cp fixture_path("beams/Elixir-Mix-Tasks-Local-Sample.beam"),
+            tmp_path("userhome/.mix/tasks/Elixir-Mix-Tasks-Local-Sample.beam")
+
+    # Run it
+    Mix.Task.run "local.sample"
+    assert_received { :mix_shell, :info, ["sample"] }
+  end
 end