Store relative paths in erlang manifest

Signed-off-by: Eric Meadows-Jönsson <eric.meadows.jonsson@gmail.com>

Author: ericmj

lib/mix/lib/mix/tasks/compile.erlang.ex

@@ -65,6 +65,8 @@ defmodule Mix.Tasks.Compile.Erlang do
         opt
     end
 
+    compile_path = Path.relative_to(compile_path, File.cwd!)
+
     tuples = files
              |> scan_sources(include_path, source_paths)
              |> sort_dependencies

lib/mix/test/mix/tasks/compile.erlang_test.exs

@@ -36,6 +36,10 @@ defmodule Mix.Tasks.Compile.ErlangTest do
       assert File.regular?("_build/dev/lib/sample/ebin/b.beam")
       assert File.regular?("_build/dev/lib/sample/ebin/c.beam")
 
+      assert File.read!("_build/dev/lib/sample/.compile.erlang") ==
+             "_build/dev/lib/sample/ebin/b.beam\n" <>
+             "_build/dev/lib/sample/ebin/c.beam"
+
       assert Mix.Tasks.Compile.Erlang.run([]) == :noop
       refute_received {:mix_shell, :info, ["Compiled src/b.erl"]}