Make sure tasks are loaded

[svrdlans]

running mix harness when asdf_elixir_version for a harness_process_manager has been set to 1.15.8-otp-25 results in the following error:

❯ mix harness
==> nimble_options
Compiling 3 files (.ex)
Generated nimble_options app
==> harness_process_manager
Compiling 1 file (.ex)
Generated harness_process_manager app
==> harness
Compiling 2 files (.ex)
error: module Projection is not loaded and could not be found. This may be happening because the module you are trying to load directly or indirectly depends on the current module
  lib/evolver.ex:4: Evolver (module)


== Compilation error in file lib/evolver.ex ==
** (CompileError) lib/evolver.ex: cannot compile module Evolver (errors have been logged)
    (elixir 1.15.8) expanding macro: Kernel.use/2
    lib/evolver.ex:4: Evolver (module)

further tinkering revealed that not all harness tasks are available when running "harness.compile" inside Mix.Tasks.Harness.run/1
in mix codebase the private fetch/1 function doesn't find the appropriate task modules for Harness.Compile and Harness.Check, maybe some others also:
https://github.com/elixir-lang/elixir/blob/4e6d67c169d75476677a768f5cff553a3c8f288b/lib/mix/lib/mix/task.ex#L316

but if we load tasks from the archive install location, then all task modules are available, and mix harness runs without issues

---

the proposed solution might not be the only one, but seems the simplest to me, and I'm open for any suggestions

[tonyvanriet]

looks nice and clean to me.
good fix

[svrdlans]

further testing reveals that even with this change, we will still need to modify our harness libraries, more precisely the mix.exs template
I've found that both of these things work:

  def application do
    [
      mod: {<%= @app |> pascal() %>.Application, []},
      extra_applications: [:logger, :runtime_tools, :sasl],
      included_applications: [:harness]
    ]
  end

or

  defp aliases do
    Code.ensure_compiled(Harness)
    Code.ensure_compiled(Harness.Manifest)
    Code.ensure_compiled(Mix.Tasks.Harness.Check)

    [
      "ecto.setup": ["ecto.create", "ecto.migrate"],
      "ecto.reset": ["ecto.drop", "ecto.setup"],
      compile: ["harness.check", "compile"],
      test: ["ecto.reset --quiet", "ecto.migrate", "test"]
    ]
  end

without one of those "harness.check" task is not available:

❯ mix bless
==> event_listener
Generated event_listener app
Running compile with args ["--warnings-as-errors", "--force"]
==> extrack_translation_pm
Generated extrack_translation_pm app
** (Mix) The task "harness.check" could not be found. Did you mean "archive.check"?

there might be a nicer way to this, but I wasn't able to find it

[tonyvanriet]

I don't have a strong intuition on which is better based on how they work internally or what's more idiomatic for Elixir. so all I'm left with is a preference for the ensure_compiled inside aliases since it at least puts the solution near the thing that depends on it in the code.

[svrdlans]

yeah, same, although I'd wrap those in a function and just have it like that:

  defp aliases do
    ensure_harness_check_is_available()

    [
      "ecto.setup": ["ecto.create", "ecto.migrate"],
      "ecto.reset": ["ecto.drop", "ecto.setup"],
      compile: ["harness.check", "compile"],
      test: ["ecto.reset --quiet", "ecto.migrate", "test"]
    ]
  end

  defp ensure_harness_check_is_available do
    [Harness, Harness.Manifest, Mix.Tasks.Harness.Check]
    |> Enum.each(&Code.ensure_compiled/1)
  end