Add nicer compiler errors when assigning a parameter to type LuckyAction.class

[stephendolan]

It seems like folks often want to write wrappers that can handle links, and will leverage the link_helper.cr definitions to figure out what to ask for in a parameter.

Something like this:

class UI::Button < BaseComponent
  needs title : String
  needs to : Lucky::Action.class
  def render
    link title, class: "btn", to: to
  end
end

Called like this:

m UI::Button, title: "Button Text", to: App::Show

Generates this cryptic compiler error:

Here's why, as noted in our Gitter:

https://github.com/luckyframework/lucky/blob/master/spec/lucky/with_defaults_spec.cr
The error is because it is saying that a Lucky::Action could be any number of Lucky::Actions which have various different arguments. So your component would need to handle all the different kind of actions for it to work correctly. What you could also try to do is make it generic by making the needs route : T and that may work
But I think that with_defaults is nice because you can use any tag method with it like button, submit etc.

Alllllll that context provided, I think it'd be really great if Lucky could step in and help out here when it seems that someone is trying to type-check a parameter with a Lucky::Action.class. Something like:

If you're trying to validate that a Lucky `link_helper` is provided, you should use a generic `needs param : T` or the built-in `with_defaults` helper.

The message needs some work, but the gist is that Lucky could point users towards what they want based on the use cases for checking a LuckyAction.class.

[paulcsmith]

An example of doing this with a generic:

class UI::Button(T) < BaseComponent
  needs title : String
  needs action : T

  def render
    link title, to: action, class: "btn"
  end
end

And with_defaults (the most flexible and preferred solution)

class UI::Button < BaseComponent
  def render
    with_defaults class: "btn" do |button_builder|
      yield button_builder
    end
  end
end

# Call *any* tag method. `link`, `button`, etc.
m UI::Button, &.link("My link, to: App::Show)

[da1nerd]

Although not preferred, the usage of the generic version does look a bit nicer if you aren't used to blocks. I guess it would just depend how flexible/reusable you want your component to be. To complete the example above here's the usage of the generic.

m UI::Button, title: "My Link", to: App::Show

and your with_defaults is missing a quote.

m UI::Button, &.link "My link", to: App::Show

[paulcsmith]

@neutrinog I agree it looks nicer especially if you are new to blocks. The downside is that you can't do something like this with the generic version since it uses a different tag than an a :(

m UI::Button, &.submit("Save my form")

I think adding parens around the block helps a bit so I'm going to start doing that form now on to hopefully clarify things a bit. We'll see :

[neurodynamic]

@paulcsmith Wrong tag I think 😛

[paulcsmith]

Oops! Sorry @neurodynamic!