[SR-11511] A returning value of Array<Void> should give a warning, like Optional<Void>

[BasThomas]

Previous ID	SR-11511
Radar	None
Original Reporter	@BasThomas
Type	Improvement
Status	Resolved
Resolution	Done

Additional Detail from JIRA

Votes	0
Component/s	Compiler
Labels	Improvement, StarterBug
Assignee	jder (JIRA)
Priority	Medium

md5: ebcfa84ec27da83a255c80a10ed317da

Issue Description:

let optOne: Int? = 1
let y = optOne.map { _ in return () } // Constant 'y' inferred to have type '()?', which may be unexpected
let z = [""].map { _ in return () } // no warning.

// The expected warning would be:
// Constant 'z' inferred to have type '[()]', which may be unexpected

For more information see the thread in this tweet.

[belkadan]

@xedin, @hborla, what do you think? Helpful or not worth it? Also, starter-bug-able or not?

[theblixguy]

Yeah, it's starter-bug worthy. We need to add another check here to account for an ArraySliceType with Void as base type.

[ZevEisenberg]

Should it also give a suggestion, like putting an extra set of parentheses or writing Void explicitly to silence the warning? Or is there no reasonable case where you would actually intend to do this?

[theblixguy]

I think there should be a fix-it to insert an explicit type annotation, I can’t remember if we do it for the Optional<Void> case as well.

[belkadan]

Looks like we don't today but we totally should.

<stdin>:2:5: warning: constant 'y' inferred to have type '()?', which may be unexpected
let y = x.map { print($0) }
    ^
<stdin>:2:5: note: add an explicit type annotation to silence this warning
let y = x.map { print($0) }
    ^

[swift-ci]

Comment by Jesse Rusak (JIRA)

I made a quick PR for these two ideas here #27797

Feedback very welcome!

[swift-ci]

Comment by Jesse Rusak (JIRA)

PR is now merged.