Allow {module, function, args} for mixin

[jechol]

Contributor checklist

• Bug fixes include regression tests
• Features include unit/acceptance tests

[rgraff]

@jechol what's the use case here as opposed to just have a module mixin? Can you update the getting started guide with an example?

[jechol]

My use case is that I want to mix-in AshAdmin's admin section with name and resource group.

defmodule Foo do
  use Ash.Resource, extensions: [AshPaperTrail.Resource]

  paper_trail do
    mixin {MyPaperTrailMixin, :mixin, ["foo", :foobar]}
  end
end

defmodule Bar do
  use Ash.Resource, extensions: [AshPaperTrail.Resource]

  paper_trail do
    mixin {MyPaperTrailMixin, :mixin, ["bar", :foobar]}
  end
end


defmodule MyPaperTrailMixin do
  def mixin(name, group) do
    quote do
      admin do
        name unquote(name)
        resource_group unquote(group)
      end
    end
  end
end

[jechol]

@rgraff I updated the guide to use the {module, function, args} format, because it provides more flexibility than the use syntax.

[rgraff]

@jechol Looks good. Thank you for your contribution. 🎉