refmterr: Special case brisk-reconciler stateless component error

[wokalski]

There's a Revery/brisk-reconciler specific error that's not obvious, it's when you use let%component but don't use hooks inside the component. You get:

This type doesn't match what is expected.

  This type:
    Brisk_reconciler.element(Revery_UI.React.node)

  Expecting:
    Brisk_reconciler__.Hooks.t('a, 'a) =>
    (
      Brisk_reconciler.element('b),
      Brisk_reconciler__.Hooks.t(Brisk_reconciler__.Hooks.nil, 'a)
    )

It'd be great to special case it and explain the root of the cause in human language.

[kyldvs]

I wonder if a better solution might be to prevent this error entirely. The ppx could always insert some sort of hook even when none are necessary.

This could always be transformed:

let%component make = () => {
  <View> someContainer </View>
};

Into this:

let%component make = () => {
  let%hook _ = Hooks.empty();
  <View> someContainer </View>
};

Not sure if that will also have some sort of perf impact too though.

[wokalski]

@kyldvs The PPX as it is now is very simple so you can do things like:

let%component component = (~prop, ()) => implementation(~prop)

Ppx can only be good and reliable if it’s simple. So I’m avoiding any additional magic. There’s enough of it already!

[jordwalke]

I wonder how we can allow customization on a per library basis. Imagine something like packages being able to append to an environment variable (like a colon separated PATH) except each segment informs refmterr about how to special case errors. What would you want this error to be formatted as?

[wokalski]

@jordwalke Instead of this:

This type doesn't match what is expected.

  This type:
    Brisk_reconciler.element(<ANYTHING>)

  Expecting:
    Brisk_reconciler__.Hooks.t('a, 'a) =>
    (
      Brisk_reconciler.element('b),
      Brisk_reconciler__.Hooks.t(Brisk_reconciler__.Hooks.nil, 'a)
    )

I'd like to match ^ that and output an error saying something along these lines:

let%component can only be used for declaring components that use hooks for state or effects. Remove %component extension if you just return an element from the component.

  This type:
    Brisk_reconciler.element(Revery_UI.React.node)

  Expecting:
    Brisk_reconciler__.Hooks.t('a, 'a) =>
    (
      Brisk_reconciler.element('b),
      Brisk_reconciler__.Hooks.t(Brisk_reconciler__.Hooks.nil, 'a)
    )