fix: improve type definitions, mark tslib as dep (#5)

.changeset/neat-toes-return.md

@@ -0,0 +1,5 @@
+---
+"synckit": patch
+---
+
+fix: improve type definitions, mark tslib as dep

README.md

@@ -39,13 +39,15 @@ const syncFn = createSyncFn(require.resolve('./worker'))
 
 // do whatever you want, you will get the result synchronously!
 const result = syncFn(...args)
+```
 
+```js
 // worker.js
 import { runAsWorker } from 'synckit'
 
 runAsWorker(async (...args) => {
   // do expensive work
-  // but you mush mark sure the `result` is serializable by `JSON.stringify`
+  // but you must make sure the `result` is serializable by `JSON.stringify`
   return result
 })
 ```

package.json

@@ -41,6 +41,7 @@
     "typecov": "type-coverage"
   },
   "dependencies": {
+    "tslib": "^2.2.0",
     "uuid": "^8.3.2"
   },
   "devDependencies": {
@@ -52,6 +53,7 @@
     "@types/uuid": "^8.3.0",
     "clean-publish": "^2.1.1",
     "npm-run-all": "^4.1.5",
+    "ts-expect": "^1.3.0",
     "ts-jest": "^26.5.5",
     "ts-node": "^9.1.1",
     "type-coverage": "^2.17.3",

src/index.ts

@@ -5,6 +5,10 @@ import fs from 'fs'
 
 import { v4 as uuid } from 'uuid'
 
+import { AnyAsyncFn, AnyFn, Syncify } from './types'
+
+export * from './types'
+
 /**
  * @link https://github.com/sindresorhus/temp-dir/blob/main/index.js#L9
  */
@@ -30,12 +34,12 @@ const isTsconfigPathsAvailable = () => {
   return tsconfigPathsAvailable
 }
 
-// eslint-disable-next-line @typescript-eslint/no-explicit-any
-const syncFnCache = new Map<string, (...args: any) => any>()
+const syncFnCache = new Map<string, AnyFn>()
 
-export const createSyncFn = <T extends (...args: unknown[]) => unknown>(
+export function createSyncFn<T extends AnyAsyncFn>(
   workerPath: string,
-) => {
+): Syncify<T>
+export function createSyncFn<R>(workerPath: string) {
   if (!path.isAbsolute(workerPath)) {
     throw new Error('`workerPath` must be absolute')
   }
@@ -59,7 +63,7 @@ export const createSyncFn = <T extends (...args: unknown[]) => unknown>(
         : /* istanbul ignore next */ '')
     : 'node'
 
-  const syncFn = (...args: Parameters<T>): ReturnType<T> => {
+  const syncFn = (...args: unknown[]): R => {
     const filename = path.resolve(tmpdir, `synckit-${uuid()}.json`)
 
     fs.writeFileSync(filename, JSON.stringify(args))
@@ -83,13 +87,9 @@ export const createSyncFn = <T extends (...args: unknown[]) => unknown>(
   return syncFn
 }
 
-// eslint-disable-next-line @typescript-eslint/no-explicit-any
-export const runAsWorker = async <R, T extends (...args: any[]) => Promise<R>>(
-  fn: T,
-) => {
+export const runAsWorker = async <T extends AnyAsyncFn>(fn: T) => {
   const filename = process.argv[2]
   const content = fs.readFileSync(filename, 'utf-8')
   const options = JSON.parse(content) as Parameters<T>
-  const result = await fn(...options)
-  fs.writeFileSync(filename, JSON.stringify(result))
+  fs.writeFileSync(filename, JSON.stringify(await fn(...options)))
 }

src/types.ts

@@ -0,0 +1,18 @@
+// eslint-disable-next-line @typescript-eslint/no-explicit-any
+export type AnyFn<T = any, R extends any[] = any[]> = (...args: R) => T
+
+// eslint-disable-next-line @typescript-eslint/no-explicit-any, @typescript-eslint/no-type-alias
+export type AnyPromise = Promise<any>
+
+// eslint-disable-next-line @typescript-eslint/no-type-alias
+export type AnyAsyncFn = AnyFn<AnyPromise>
+
+export type Syncify<T extends AnyFn<AnyPromise>> = T extends (
+  ...args: infer Args
+) => Promise<infer R>
+  ? (...args: Args) => R
+  : never
+
+export type PromiseType<T extends AnyPromise> = T extends Promise<infer R>
+  ? R
+  : never

test/types-d.ts

@@ -0,0 +1,33 @@
+/* eslint-disable @typescript-eslint/no-floating-promises */
+import { TypeEqual, expectType } from 'ts-expect'
+
+import {
+  AnyPromise,
+  createSyncFn,
+  PromiseType,
+  runAsWorker,
+  Syncify,
+} from 'synckit'
+
+// @ts-expect-error
+expectType<Syncify<() => 1>>(true)
+
+expectType<TypeEqual<Syncify<() => Promise<true>>, () => true>>(true)
+expectType<TypeEqual<Syncify<() => AnyPromise>, () => PromiseType<AnyPromise>>>(
+  true,
+)
+expectType<TypeEqual<Syncify<() => Promise<never>>, () => never>>(true)
+
+// @ts-expect-error
+createSyncFn<() => 0>('')
+
+// @ts-expect-error
+expectType<() => true>(createSyncFn<() => Promise<1>>(''))
+
+expectType<() => true>(createSyncFn<() => Promise<true>>(''))
+expectType<() => true>(createSyncFn<() => Promise<never>>(''))
+
+// @ts-expect-error
+runAsWorker(() => 1)
+
+runAsWorker<() => Promise<number>>(() => Promise.resolve(1))

yarn.lock

@@ -9615,6 +9615,11 @@ trough@^1.0.0:
   resolved "https://registry.yarnpkg.com/trough/-/trough-1.0.5.tgz#b8b639cefad7d0bb2abd37d433ff8293efa5f406"
   integrity sha512-rvuRbTarPXmMb79SmzEp8aqXNKcK+y0XaB298IXueQ8I2PsrATcPBCSPyK/dDNa2iWOhKlfNnOjdAOTBU/nkFA==
 
+ts-expect@^1.3.0:
+  version "1.3.0"
+  resolved "https://registry.yarnpkg.com/ts-expect/-/ts-expect-1.3.0.tgz#3f8d3966e0e22b5e2bb88337eb99db6816a4c1cf"
+  integrity sha512-e4g0EJtAjk64xgnFPD6kTBUtpnMVzDrMb12N1YZV0VvSlhnVT3SGxiYTLdGy8Q5cYHOIC/FAHmZ10eGrAguicQ==
+
 ts-jest@^26.5.5:
   version "26.5.5"
   resolved "https://registry.yarnpkg.com/ts-jest/-/ts-jest-26.5.5.tgz#e40481b6ee4dd162626ba481a2be05fa57160ea5"