[Proposal] Add a feature to put Makefile in Application.app_dir

[zacky1972]

Hi,

I propose Add a feature to put Makefile in Application.app_dir(:app, "somewhere") , especially in case that the Makefile is generated by a macro, e.g. in case of Pelemay.

The following error occurs by setting :make_makefile to Applicatoin.app_dir(:app, "somewhere/Makefile") in project in mix.exs:

❯❯❯ mix deps.get
** (ArgumentError) unknown application: :elixir_make_test
    (elixir 1.11.2) lib/application.ex:896: Application.app_dir/1
    (elixir 1.11.2) lib/application.ex:923: Application.app_dir/2
    mix.exs:11: ElixirMakeTest.MixProject.project/0
    (mix 1.11.2) lib/mix/project.ex:790: Mix.Project.get_project_config/1
    (mix 1.11.2) lib/mix/project.ex:114: Mix.Project.push/3
    (stdlib 3.13.2) lists.erl:1267: :lists.foldl/3

[josevalim]

Unfortunately we can't make that work because of a chicken and egg issue. When we are loading the mix.exs file, the application has not been defined nor compiled yet, so we can't access such paths. :(

[zacky1972]

I see. Thanks.

[zacky1972]

Excuse me,

I guess :code.priv_dir(:my_app) can be used instead of Application.app_dir(:my_app, "somewhere").
So, I propose an alternative approach that uses :code.priv_dir(:my_app), again.

[josevalim]

Application.app_dir uses :code.priv_dir, so that would have the same issue as above!

[zacky1972]

@josevalim I guess it won't work if you write :code.priv_dir and/or Application.app_dir in mix.exs, while it will work if you write them in Mix.Tasks.*.
So, it will work by describing mix.exs using an optional switch: make_in_priv_dir: true.

[josevalim]

We could make the directory customizable, and then you can pass whatever you want. I can get behind that. :)