feat: add getIsAsync helper

Author: sxzz

README.md

@@ -51,6 +51,23 @@ const result = myFunction.sync('./some-file.js')
 const asyncResult = await myFunction.async('./some-file.js')
 ```
 
+### `getIsAsync`
+
+Returns a boolean indicating whether the current execution is in async mode.
+
+```ts
+import { getIsAsync, quansync } from 'quansync'
+
+const fn = quansync(function* () {
+  const isAsync: boolean = yield* getIsAsync()
+  console.log(isAsync)
+})
+
+fn.sync() // false
+await fn() // true
+await fn.async() // true
+```
+
 ## Build-time Macro
 
 If you don't like the `function*` and `yield*` syntax, we also provide a build-time macro via [unplugin-quansync](https://github.com/unplugin/unplugin-quansync#usage) allowing you use quansync with async/await syntax, while still able to get the sync version out of that.

src/index.ts

@@ -138,3 +138,10 @@ export function toGenerator<T>(promise: Promise<T> | QuansyncGenerator<T> | T):
     return promise
   return fromPromise(promise)()
 }
+
+/**
+ * @returns `true` if the current context is async, `false` otherwise.
+ */
+export function* getIsAsync(): Generator<typeof GET_IS_ASYNC, boolean, unknown> {
+  return !!(yield GET_IS_ASYNC)
+}

test/index.test.ts

@@ -1,5 +1,5 @@
 import { expect, it, vi } from 'vitest'
-import { quansync, toGenerator } from '../src'
+import { getIsAsync, quansync, toGenerator } from '../src'
 import { quansync as quansyncMacro } from '../src/macro'
 
 it('basic', async () => {
@@ -282,3 +282,13 @@ it('call onYield hook', async () => {
   expect(() => run2.sync()).toThrowErrorMatchingInlineSnapshot(`[TypeError: custom error]`)
   await expect(run2.async()).resolves.toMatchInlineSnapshot(`"foo"`)
 })
+
+it('getIsAsync', async () => {
+  const fn = quansync(function* () {
+    const isAsync: boolean = yield* getIsAsync()
+    return isAsync
+  })
+  await expect(fn.async()).resolves.toBe(true)
+  await expect(fn()).resolves.toBe(true)
+  expect(fn.sync()).toBe(false)
+})