自定义混合任务在运行时不触发编译

Question

I've got a custom mix task. its working perfectly, however, it is not triggering a compile when it is called like other mix tasks do. I can run the compile manually but this is very frustrating as I almost always forget to do it and have to run the task once or twice before I realize why I'm not seeing my changes.

Here is "my" task, what am i missing?

defmodule Mix.Tasks.Return do
  @moduledoc """
  Task for processing returns
  """
  use Mix.Task
  require Logger
  alias Returns

  @shortdoc "Check for returns and process"

  def run(args) do
    args
    |> get_return_file_name()
    |> Returns.process()
    |> Kernel.inspect()
    |> Logger.info()
  end

  defp get_file_name(nil), do: get_file_name([])
  defp get_file_name([]), do: get_default_file_name()
  defp get_file_name([filename]), do: filename

  defp get_default_file_name() do
    DateTime.utc_now() 
    |> DateTime.to_string()   
    |> String.split(" ")  
    |> List.first()
    |> (fn date -> "default-#{date}.txt" end).()
  end
end

Answer 1

You need to explicitly say in your task that you want to compile.

@impl true
def run(args) do
  ...
  Mix.Task.run("compile")
  ...

A couple examples are app.tree , app.start and phx.routes .

This is because not all mix tasks require the compilation step. For example, mix deps.get does not compile the project before fetching dependencies, else you may have lots of errors/warnings about missing modules. All the dependencies should be called manually, there is no implicit mechanism to call chains of tasks according to some “internal rules” built into mix .

Answer 2

The Mix.Task.run("compile") fix may not actually work. José Valim has this suggestion:

That's because if they are recompiled, you won't execute the new module version in memory. A work-around is for you to do this:

def run(args) do
  Mix.Task.run("compile")
  __MODULE__.compiled_run(args)
end

def compiled_run(args) do
  ...
end

That will force it to pick the latest version of the module. Although this is probably something we should tackle in Elixir itself.