Assigning a @type to an async function emits an error

🔎 Search Terms

ts1065 jsdoc async return promise

🕗 Version & Regression Information

• This changed between versions 5.1.6 and 5.2.2

⏯ Playground Link

https://www.typescriptlang.org/play?ts=5.2.2&filetype=js#code/PQKhAIAEBcE8AcCmATRAzcBvAFASnALwB84ACgE4D2AtgJYDOiAPAG6W3IkA+4bHAvuACC9WADsAxgDEx4EMABQC0BBgJEWEeOljB8hRMpj60cNVhbJMwuACGoyeDyESmfkA

💻 Code

JSDoc version:

/** @typedef {() => Promise<void> | void} AsyncFn */

/** @type {AsyncFn} */
const myAsyncFn = async () => {}

TypeScript equivalent:

type AsyncFn = () => Promise<void> | void;

const myAsyncFn : AsyncFn = async () => {}

🙁 Actual behavior

JSDoc version emits an error, TypeScript equivalent does not.

🙂 Expected behavior

Neither should emit an error.

Additional information about the issue

I'm fairly sure this is related to a change from a while back where a new Promise needs to be explicitly marked as returning Promise<void>, which was intentional. But I can't seem to find the related issue anymore so I'm not sure if this is intentional as well.

Either way, the fact that this error is only emitted in JavaScript files seems to suggest that it's a bug.

Start with the linked TypeScript Playground repro and compare the diagnostics for the JSDoc and TypeScript examples across the reported versions. Trace the JavaScript JSDoc type-checking entry point, add regression coverage for the async function assignment, and verify that neither example emits an error.