Elixir - Mix

21 May 2017

common tasks
Phoenix tasks
mix.exs
tips
- (how to) run multiple tasks at once
- (how to) set default environment for any task
troubleshooting
- Mix doesn’t allow to run the same task twice in alias

Mix assumes that we are in the development environment unless we tell it otherwise with MIX_ENV= mix some_task.

common tasks

mix compile

compiles the whole project including dependencies.
mix deps.compile [<package>]

compiles project dependencies only (say, when you need to recompile dependencies after editing their source code manually).
mix deps.get = bundle install

gets all missing and out of date dependencies (updates existing ones up to the version specified in mix.lock).
mix deps.clean --unused --unlock = bundle install

removes dependencies which are no longer listed in mix.exs (--unused) and updates mix.lock (--unlock).
mix deps.update --all = bundle update

updates all dependencies and writes updated versions to mix.lock.
mix deps.update <package> = bundle update <gem>

updates dependency and writes updated version to mix.lock.

Phoenix tasks

mix phx.server = rails server
mix phx.routes = rake routes
mix phx.gen.secret = rake secret

mix.exs

http://blog.plataformatec.com.br/2016/07/understanding-deps-and-applications-in-your-mixfile/

application name
```
def project do
  [
    app: :neko,
    ...
  ]
end
```
- stored in neko.app (created when project is compiled)
- used to start/stop application manually in IEx

application inference

http://elixir-lang.org/blog/2017/01/05/elixir-v1-4-0-released/#application-inference

deps should be no longer listed in applications list explicitly:

def application do
  [
    # this line is longer necessary - all dependencies
    # are added to `applications` by default in Elixir 1.4
    #applications: [:httpoison],
    # specify only extra applications from Erlang/Elixir
    extra_applications: [:logger],
    mod: {Neko.Application, []}
  ]
end

defp deps do
  [
    {:httpoison, "~> 0.11.1"}
  ]
end

tips

(how to) run multiple tasks at once

$ mix do deps.get, compile

which is equivalent to:

$ mix deps.get && mix compile

(how to) set default environment for any task

https://hexdocs.pm/mix/Mix.Task.html#module-attributes

@preferred_cli_env - recommends environment to run task. It is used in absence of a Mix project recommendation, or explicit MIX_ENV, and it only works for tasks in the current project.

# mix.exs

def project do
  [
    # ...
    preferred_cli_env: [
      deploy: :prod
    ]
  ]
end

troubleshooting

Mix doesn’t allow to run the same task twice in alias

Rake has the same behaviour - task must be reenabled explicitly before it can be run again.

thus it’s impossible to create alias in mix.exs for the list of tasks in which the same task is run multiple times with different arguments:

defp aliases do
  [
    # works
    "ecto.reset": ["ecto.drop", "ecto.setup"],
    # doesn't work (the 2nd task is not run)
    "deploy.prod": [
      "edeliver build release",
      "edeliver deploy release production"
    ]
  ]
end

alternating between 2 tasks doesn’t reenable the 1st task:

defp aliases do
  [
    "edeliver.all": [
      "edeliver build release",
      "deps.get",
      # edeliver task is not reenabled
      "edeliver deploy release production"
    ]
  ]
end

solution

it’s possible to pass function instead of a string with task name and task arguments - that function would need to use Mix.Task.rerun/2 to run the same task multiple times (it reenables the task before running it):

defp aliases do
  [
    "deploy.stage": [
      &deploy_stage/1,
      "cmd ssh devops@billing sudo systemctl restart billing_stage"
    ]
  ]
end

defp deploy_stage(_) do
  Mix.shell().info("[billing staging]")
  Mix.Task.run(:edeliver, ["update", "staging", "--mix-env=stage"])
  Mix.Task.rerun(:edeliver, ["migrate", "staging"])
end

for some reason it’s required to define function with arity of 1 - otherwise Mix complains:

(FunctionClauseError) no function clause matching in Mix.Task.run_alias/3

tap349