Mix: Use relative symlinks for ebin folder

[jni-]

Mix creates symlinks between the _build/ and deps/ folder using absolute paths.

This could be the source of an issue on heroku, using relative symlinks might fix it.

Also, I think this would be cleaner since it would be self-contained and could survive moving the folder.

I started working on this in a branch called "mix_rel_symlink" on my fork, but it doesn't work yet, don't use it! It's broken. I pushed this broken commit to get feedback, I'd just like to know if I'm headed in the right direction (I'm still an elixir noob).

Thanks!

[ericmj]

I think this is a good idea, the symlinks should definitely be relative so that the project can be moved without breaking.

@jni- I looked at your branch, you can use Path.relative_to/2 instead of using common_path/2.

[edgurgel]

Same issue here! Looking forward this modification! 👍

[jni-]

I updated the branch to something that should work : https://github.com/jni-/elixir/tree/mix_rel_symlink

You can use this buildpack to test it on heroku : https://github.com/jni-/heroku-buildpack-elixir

However, even my pristine elixir clone doesn't pass the tests. I'm trying to see why it is so before I submit a pull request, to make sure I don't break anything. If your tests pass, can you checkout my repo and test it too please?

@ericmj Didn't know it existed, thanks for the tip! I started using it, but it wasn't exactly what I wanted after all.

[edgurgel]

@jni-, I pulled your branch and tests are passing here. If you submit a PR, travis-ci will run your tests. Don't worry :)

[jni-]

@edgurgel thanks! I guess my work experience with TFS has made me doubtful of CI builds =P I submitted a pull request.

This should also fix goshacmd/heroku-buildpack-elixir#9. Worked for my heroku project at least.