[unawaited_futures] does not complain for async function that return void

[stephane-archer]

if my function is :
Future<void> _foo() async {
the linter will complain if I don't await _foo()
but if my function is:
void _foo() async {
no complain.
I know I'm not "unawait a future" here but what I want is to await all async functions even if they return void over Future<void>

[eernstg]

The support for having return type void with a function whose body is async exists specifically in order to indicate that the caller should not await the future. This can be used for a task that should be initiated, but where clients are never expected to wait for its completion (e.g., it might free some resources, add a line to a log file, etc). So the standard advice would be to stop using the return type void in this situation (or stop wanting to wait for it ;-).

[lrhn]

is to await all async functions

Your code doesn't know, and mustn't know, if a function it calls is async. All it should depend on is whether the function returns a Future or not, as defined by its return type.
It's a non-breaking change, not even worthy of a minor semver version increment, to change a function implementation from async to not, or the other direction. That a function body uses async is an implementation detail that can change at any time.

So, as @eernstg says, if you don't want the future of _foo to be lost, make sure the return type is a Future type. That's how you communicate to the rest of the program that there is a future to await.

[stephane-archer]

I see, my function returned void and not future void by mistake. I usually want my fonction to wait the function it calls before continuing execution. Usually this linter helps me do that (it's really easy to forget to await a future void). Because of the exception model for error handling returning future void is quite common in my code base. Do you think it's normal or should I do something different?

[eernstg]

You could enable avoid_void_async in order to get a heads-up whenever there is a function whose body is async and whose return type is void.

This makes sense if you almost never want to write a "fire and forget" async function, and then you can mark the ones you might have anyway with // ignore: avoid_void_async and possibly a comment that explains why this function is an exception.

[stephane-archer]

I didn't notice this linter, thanks for mentioning it, I will use it moving forward 🙏

[srawlins]

Duplicate of #836