let%component ppx transforms type annotation incorrectly

[glennsl]

Type annotations on let%component functions are transformed to apply to only the return value, not the entire function.

1. Annotation of return type

module ShouldAllowComponentProp = {
  let%component make = (~component, (), hooks): element(node) =>
    (<Div> component </Div>, hooks);
}

Transforms to:

module ShouldAllowComponentProp =
  struct
    let make =
      let brisk-component =
        Brisk_reconciler.Expert.component ~useDynamicKey:false
          "test/Components.re.ShouldAllowComponentProp.make" in
      fun ?(key= Brisk_reconciler.Key.none) ->
        fun ~component ->
          fun () ->
            brisk-component ~key
              (fun hooks ->
                 (((let brisk-component = Div.make in
                    ((brisk-component
                        ~children:(Brisk_reconciler.Expert.jsx_list
                                     [component]) ())
                      [@JSX ])), hooks) : node element))
  end

Which produces the type error:

File "test/Components.re", line 239, characters 4-35:
239 |     (<Div> component </Div>, hooks);
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Error: This expression has type 'a * 'b
       but an expression was expected of type node element

2. Annotation of entire function type

module ShouldAllowComponentProp = {
  let%component make
    : (~key:int=?, ~component: element(node), unit) => element(node) 
    = (~component, (), hooks) =>
      (<Div> component </Div>, hooks);
}

Transforms to:

module ShouldAllowComponentProp =
  struct
    let make =
      let brisk-component =
        Brisk_reconciler.Expert.component ~useDynamicKey:false
          "test/Components.re.ShouldAllowComponentProp.make" in
      fun ?(key= Brisk_reconciler.Key.none) ->
        brisk-component ~key
          (fun ~component ->
             fun () ->
               fun hooks ->
                 ((let brisk-component = Div.make in
                   ((brisk-component
                       ~children:(Brisk_reconciler.Expert.jsx_list
                                    [component]) ())
                     [@JSX ])), hooks) : ?key:int ->
                                           component:node element ->
                                             unit -> node element)
  end

Which produces the error:

File "test/Components.re", line 240, characters 4-62:
240 |     (~component, (), hooks) => (<Div> component </Div>, hooks);
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Error: This function should have type
         ?key:int -> component:node element -> unit -> node element
       but its first argument is labelled ~component