Generator that never returns should have return type 'never'

[KSXGitHub]

Search Terms

Suggestion

Generator function that yields T but never return should return Generator<T, never, unknown>

function * generator<T> (x: T) {
  while (true) yield x
}

const iter = generator(3) // expect: Generator<number, never, unknown>

Use Cases

Examples

Checklist

My suggestion meets these guidelines:

• [ ] 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.

[AnyhowStep]

https://github.com/microsoft/TypeScript/issues/11296#issuecomment-267094790

https://github.com/microsoft/TypeScript/issues/16608

https://github.com/microsoft/TypeScript/pull/8767

[RyanCavanaugh]

Appreciate the links @AnyhowStep but I don't think the motivation for hiding never return types in function declarations necessarily applies to generator functions.

@rbuckton thoughts?