Infer non returning function to be returning `undefined`, not `void`

Search Terms

non returning, undefined instead of void, undefined or unknown instead of void

Suggestion

• Change return of non returning functions to undefined instead of void
• Accept unknown as a type of non returning functions
  examples:

const f = () => {} // this gets inferred as () => void

const f1 = (): undefined => {} // doesn't work
// error: A function whose declared type is neither 'void' nor 'any' must return a value.(2355)

const f2 = (): unknown => {} // same error

https://www.typescriptlang.org/play/#code/MYewdgzgLgBAZjAvDAFASiQPhgbwL4CwAUMaJLHAIxKpoBcMArmACYCmcAlmGy1rjEIkiZaPABMNdA2YBrMCADuYfvmJA

Motivations

void is an annoying type to deal with, has many inconsistencies and there's a ton of issues around it for its weird behavior like: #35850 , #35236 , #33420 ... etc
Non-returning functions actually return undefined which is a more predictable type to deal with and narrow disjunctions with and even use optional chaining with.

Use Cases

Many use cases appear while using promises where there's a need to catch an error but at the same time not deal with void

const f = () => {}
async (p: Promise<A>) => {
  const a = await p.catch(f);
  // do stuff with a whose type is now A | void
};

Checklist

My suggestion meets these guidelines:

• This wouldn't be a breaking change in existing TypeScript/JavaScript code

Not sure if this might break some code or not but I think any code that dealt with void should work while dealing with undefined?

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

Aucun fichier source ni test n’est nommé. Commencez par les exemples d’inférence et le playground TypeScript lié, puis examinez comment le passage de void à undefined pour les fonctions ne retournant rien affecte les cas d’utilisation des promises et du narrowing. Le travail serait considéré comme terminé lorsqu’un design résolu du système de types pour le comportement proposé de undefined et unknown serait défini.