Custom Mix Task to generate ex files

Question

I'm currently trying to write a mix task that automates the scaffolding of an Elm app in a phoenix (v1.3) project. It's generating all the elm files / js script to add, installing node and elm modules correctly. I'm also generating an elm_view.ex and elm_controller.ex that takes the name of the current otp_app, and it outputs the files correctly like below:

defmodule PipeDream.Web.ElmController do
  use PipeDream.Web, :controller

  def index(conn, _params) do
    render conn, "index.html"
  end
end

However, when I start the server with mix phx.server I get an error: "module PipeDream.Web.ElmController is not available". I've found that when I go to these files and save them the module gets picked up correctly (similar error with the elm_view.ex).

Could this be something to do with how I'm rendering the controller and view templates? The templates look like this:

defmodule <%= @app_name %>.Web.ElmController do
  use <%= @app_name %>.Web, :controller

  def index(conn, _params) do
    render conn, "index.html"
  end
end

and I'm using EEx.eval_string(template_string, assigns: [app_name: app]) to add the app module name and then writing the file with Mix.Generator.create_file

Would be super grateful for any help or suggestions!

So the files are created on the disk, but mix phx.server only picks it up after you manually open the file in an editor and save them (without making any changes)? — Dogbert
Can you post the source of the Mix task (where you call create_file etc)? — Dogbert
sure, this is the mix task file: github.com/TechforgoodCAST/pipe-dream/blob/master/lib/mix/tasks/… — Andrew MacMurray
I believe there could be an issue with file creation time. Just out of curiosity, would you File.touch/2 the newly created file with localtime given as the second parameter? Also, I suggest you to use Mix.Generator.embed_template/2 to compile and embed template. — Aleksei Matiushkin

Aleksei Matiushkin Aleksei Matiushkin · Accepted Answer · 2017-05-18T05:36:55

Since there are many comments above, I decided to post a [hacky but yet working] solution as an answer for the future visitors.

There is some kind of file creation time issue when Elixir/Mix try to cache/check the dependencies. While the sledgehammer solution proposed by Steve Pallen (rm -rf deps && rm -rf _build && mix do deps.get, deps.compile, compile) should work always, there might be a more handy hack: call File.touch/2 on newly generated files to enforce Mix to recompile them.

Also, as a sidenote, I would suggest to use Mix.Generator.embed_template/2 to compile and embed template, rather than generic EEx.eval_string to clarity the intent.

Custom Mix Task to generate ex files

1 Answers