Boundary - enforcing boundaries in Elixir projects

This looks very nice! I hope to find some time to play with it soon.

One question I had while reading. I was wondering what the reason is that the root module is always exported?

This is exactly how I imagine boundries to be reasonably enforced and it’s even part of elixir LS.

There are two reasons. One is mechanical, another conceptual.

The mechanical is that allowing root export to be configurable makes configuration a bit more messy. For example, let’s say we want to export MySystem and MySystem.User. There are two options:

{MySystem, exports: [MySystem, MySystem.User]}

Here, we require that the exported modules are referenced with the full name which makes the configuration more noisy. It can become a significant problem if we’re dealing with 2nd (or 3rd, or 4th, …) level boundaries (which is an addition I’m definitely considering).

Another option is to introduce some sort of special atom such as :this, or :root:

{MySystem, exports: [:root, MySystem.User]}

which looks a bit ugly/hacky to me.

The conceptual problem is that I’m somewhat skeptical that exporting e.g. MySystem.User, while keeping MySystem internal is a good code organization. If you want to have some internal helper functions, I think that using e.g. MySystem.Helpers or some such is a better approach. To be clear, I definitely don’t want boundaries to be highly opinionated and rigid, but given the mechanical issues presented earlier, and this conceptual problem, I currently opted to always export the root module.

In any case, none of the current choices is set in stone, so this decision is definitely up for discussion (in which case perhaps a GH issue would be a better place).

I was just wondering about the the reasons. Both reasons look valid.

Elixir LS has support for boundaries? Where can I read about that?

Look at the github readme.

I think that what @LostKobrakai tries to say is that boundaries integrates with ElixirLS, because it’s a mix compiler, and ElixirLS can work with mix. This is mentioned in the boundaries readme near the end:

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Ah, now I get it. Thanks. I completely misinterpreted that.

First off this is a VERY interesting project! It’s really neat to be able to define enforced boundaries in such a succinct way. A tool like this could help an Elixir project stay in one application for much longer before feeling a need to move to an umbrella or poncho style with multiple applications.

I agree that it makes sense to export the root module by default. But in order to have a flexible tool it would be nice to optionally not export a root module. Perhaps a syntax like this could work:

{MySystem, exports: [MySystem.User], export_root: false}

Looking at this on my phone, but I didn’t see it mentioned anywhere how this interacts with the standard library and packages. Do they also need to be defined as boundaries? Also, I suspect this wouldn’t catch modules passes as variables? Would it notice you reference a module to store it into a variable?

This is a great project. I ran it against a small app I’ve been working on and found a couple of useful violations. Definitely think something like this has legs.

If others run into a bug when reporting on .eex files I posted a fix in GitHub.
https://github.com/sasa1977/boundaries/issues/1