[RFC] Slice Linting

[jgwhite]

Summary

Add linting and/or tests that promote the addition of validation to Slice models.

Motivation

Templates that depend upon data which may not be available is a common source of errors in Slices.

For example, consider FooSlice:

# app/slices/foo/foo_slice.rb

class FooSlice < Slice
  field :bar, type: String
end

<!-- app/slices/foo/views/show.html.erb -->

<p><%= bar.upcase %></p>

If bar is nil (which it will be by default) this will raise a NoMethodError and the entire page will fail to render.

Rather than introduce null checking to templates, we would prefer to enforce these dependencies at the slice-model level:

# app/slices/foo/foo_slice.rb

class FooSlice < Slice
  field :bar, type: String
  validates :bar, presence: true
end

This enforces consistency at a lower level and prevents both full blown render failures and incorrect renders.

[erino]

That's a great idea, but considering that we've always been able to do this, do you think we should add something to the generators to highlight this as a potential issue?

We could always add a default and a commented out validation?

class FooSlice < Slice
  field :bar, type: String, default: ''
  # validates :bar, presence: true
end

[jgwhite]

@erino good point, generators should definitely include validation hints too.

[bensymonds]

I think it depends on how we're expecting Slices to be used, and by whom. In the end when you're creating a Slice you're still programming, so you should be thinking about validation and things like that anyway, so it almost doesn't need saying. But if the idea is that you don't need to have knowledge of how ActiveModel (or whatever) is meant to be used, then yes maybe we should make it clearer. Adding bits to the generator is easy enough; adding automagic testing is even better! But harder.

[jgwhite]

@bensymonds I’d say Rails knowledge is a prerequisite for using Slices.

[bensymonds]

Well then! It might be hard to draw the line about what we do mention in generators and what we don't. E.g. should we also have some example callback hooks?

The automated test thing would still be useful though, because it covers accidental omission (as opposed to not knowing to put them in in the first place).