Output function name based on constant string

One option that comes to mind is to bind to module as an external, which would let you treat index.js’s exports as a dictionary:

// Firebase.res
type request
type response = JSON.t
type apiCallback

@module("firebase-functions/v2/https")
external onCall: (request => response) => apiCallback = "onCall"

// ApiDefinition.res
let myAction = "myAction"
let myOtherAction = "myOtherAction"

// ApiImpl.res
let myAction = Firebase.onCall(_ => JSON.Number(42.0))
let myOtherAction = Firebase.onCall(_ => JSON.String("Hello!"))

// Index.res
type module_ = {
  mutable exports: Js.Dict.t<Firebase.apiCallback>
}

external module_: module_ = "module"

module_.exports = Js.Dict.fromArray([
  (ApiDefinition.myAction, ApiImpl.myAction),
  (ApiDefinition.myOtherAction, ApiImpl.myOtherAction),
])