Union returntype with void must return a value

[Pajn]

I have a method declared as stop(): void|Promise<void> {} which get the error

A function whose declared type is neither 'void' nor 'any' must return a value

As void is a valid return type I would expect that to be fully valid code. Specifying only void is working.

[RyanCavanaugh]

Proposing changing spec section 6.3

An explicitly typed function whose return type isn't the Void or the Any type must have at least one return statement somewhere in its body

to

An explicitly typed function whose return type isn't the Void type, the Any type, or a union type containing the Void or Any type as a constituent must have at least one return statement somewhere in its body

[DanielRosenwasser]

That still doesn't actually cover Promise<void> on its own though.

[RyanCavanaugh]

Not sure I understand the comment

[DanielRosenwasser]

The change you're proposing doesn't permit an async function whose return type annotation is Promise<void> to have no return statements.

[RyanCavanaugh]

I don't think anyone would want that behavior (@Pajn, care to weigh in?)

[Pajn]

It would be nice if Promise didn't require a return statement in an async function. However for the issue I had the already proposed change would be enough.

[RyanCavanaugh]

Approved, accepting PRs. Should be easy.

[masaeedu]

@RyanCavanaugh Regarding:

An explicitly typed function whose return type isn't the Void type, the Any type, or a union type containing the Void or Any type as a constituent must have at least one return statement somewhere in its body

Isn't the emphasized part redundant? The following already compiles:

function f(): number | any {
}

I think the union resolution already recognizes that all types are subtypes of any, so any union involving any is just any.

[RyanCavanaugh]

I think that's an implementation side effect of the compiler. The spec doesn't specify that number | any is equivalent to the Any type, though.