async function needs Promise<T> return type quick fix

[JacksonKearl]

Search Terms

• return type quick fix
• async function quick fix
• global promise type

Suggestion

It would be nice if TypeScript contributed a quick fix to resolve The return type of an async or global function must be the global Promise<T> type errors. The fix would simply wrap the existing return type into a Promise.

Checklist

My suggestion meets these guidelines:

• [x ] This wouldn't be a breaking change in existing TypeScript/JavaScript code
• [ x] This wouldn't change the runtime behavior of existing JavaScript code
• [ x] This could be implemented without emitting different JS based on the types of the expressions
• [x ] This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, etc.)
• [x ] This feature would agree with the rest of TypeScript's Design Goals.

[DanielRosenwasser]

Could you provide an example of a before and after of the code fix? It's not clear what fix you're expecting.

[JacksonKearl]

Before:

async doThing(): boolean { // Err: The return type of an async function must be the global Promise<T> type

}

After:

async doThing(): Promise<boolean> {

}

[Kingwl]

Related: #35300

[DanielRosenwasser]

We should create a new specialized diagnostic for when the given type isn't assignable to PromiseLike<any> to add Did you mean to write 'Promise<{0}>'?

Then provide a quick fix to write Promise<{0}>.

[DanielRosenwasser]

Looks like this didn't make it into 3.9. Will have to review with @mjbvz and @RyanCavanaugh whether it goes into 3.9.3 or 4.0

[JacksonKearl]

!!!

hell yes