[Feature]: Remove compile-time dependency on permissions module

[maltoe]

Problem description

Hi 👋

first of all, thank you for this great library! We are currently adding it to our application and are really happy with the framework it provides us with so far. 👍

We noticed that use Permit, permissions_module: MyApp.Permissions introduces a compile-time dependency from our MyApp.Authorization to MyApp.Permissions, which is unfortunate as the latter has quite a few runtime dependencies to schema & context modules of our app, and hence every change to e.g. MyApp.User causes MyApp.Authorization to be recompiled.

It appears that the reason for this compile-time dependency is the way you access the actions_module through the permissions module at compile-time in order to generate a matching set of predicate functions.

permit/lib/permit.ex

Lines 117 to 118 in 4d1c407

	Macro.expand(permissions_module, __CALLER__).actions_module()
	|> Permit.Actions.list_groups()

Proposed solution

We'd like to ask you to consider removing this compile-time dependency in favor of another explicit actions_module option in Permit.__using__/1. Arguably introduces some redundancy and potential for mismatch between the values given to both modules, but it's a "one-time surprise" type of issue vs. yet another file that needlessly gets recompiled frequently (yes, we used to have a lot of them 🙂 ).

To keep backwards compatibility, you could make it optional and fallback to the access through permissions module:

    actions_module =
      case Keyword.get(opts, :actions_module) do
        nil -> Macro.expand(permissions_module, __CALLER__).actions_module()
        module -> Macro.expand(module, __CALLER__)
      end

Checklist

• I have searched for existing issues before creating this one
• I have checked the roadmap in the README
• This is a feature request, not a bug report or question. For general questions, please use Elixir Slack's Permit channel.

[edit] ☝️ actually, this could be related to #23 and/or #24 but not sure

[vincentvanbush]

Hi @maltoe, thanks a lot for reaching out - it's a good catch; as we're currently occupied preparing a batch of changes for a minor version upgrade for Permit.Phoenix, would you mind attempting to tackle this if you've got a ready implementation idea in mind? Otherwise we'll try prioritizing this with our resources.

[maltoe]

Can do, but you need to make the call about backwards compatibility. Personally, I'd just make the actions_module option required in Permit.__using__/1, TBH. Wdyt?

[maltoe]

See PR. Stopped short of filling out all your checklist items, will continue later once you say the approach is ok and go through it.

[maltoe]

@vincentvanbush 👋 If you just tell me whether it's ok to break backwards compatibility and make actions_module mandatory, I'd polish the PR a bit.

[vincentvanbush]

Hi @maltoe, sorry for this taking so long. It's fine with us. Feel free to do anything else you'd like to do to polish this. 👍