index.ts

// https://github.com/mobxjs/mobx/discussions/2850#discussioncomment-497321

import {
  $mobx,
  AnnotationsMap,
  CreateObservableOptions,
  isObservable,
  makeObservable
} from 'mobx'

const annotationsSymbol = Symbol()
const objectPrototype = Object.prototype

type NoInfer<T> = [T][T extends any ? 0 : never];
type Annotations<T extends Object = Object, U extends PropertyKey = never> = AnnotationsMap<T, U>;

const makeAutoObservable = <
  T extends object & { [annotationsSymbol]?: any },
  AdditionalKeys extends PropertyKey = never
>(
    target: T,
    overrides?: Annotations<T, NoInfer<AdditionalKeys>>,
    options?: CreateObservableOptions
  ): T => {
  // Make sure nobody called makeObservable/makeAutoObservable/extendObservable/makeSimpleAutoObservable previously (eg in parent constructor)
  if (isObservable(target)) {
    throw new Error('Target must not be observable')
  }

  let annotations = target[annotationsSymbol]

  if (!annotations) {
    annotations = {} as Annotations

    let current = target
    while (current && current !== objectPrototype) {
      Reflect.ownKeys(current).forEach(key => {
        if (key === $mobx || key === 'constructor') return
        annotations![key] = !overrides ? true : key in overrides ? overrides[key as keyof typeof overrides] : true
      })

      current = Object.getPrototypeOf(current)
    }

    // Cache if class
    const proto = Object.getPrototypeOf(target)
    if (proto && proto !== objectPrototype) {
      Object.defineProperty(proto, annotationsSymbol, {value: annotations})
    }
  } else {
    // Apply only annotations existed in target already
    // https://github.com/mobxjs/mobx/discussions/2850#discussioncomment-1396837
    const tmp = {} as Annotations<Object, any>
    for (const key in target) {
      if (annotations[key]) {
        tmp[key] = annotations[key]
      }
    }
    annotations = tmp
  }

  return makeObservable(target, annotations, options)
}

export default makeAutoObservable