[SR-1752] Fix warning about unused result if return type is Void?

[ahoppen]

What's in this pull request?

Right now, if a function has a return value of Optional<Void> a warning about an unused result is generated. This also applies for the use of optional chaining inside a ternary operator, e.g. if c.f() returns Void and you do true ? c?.f() : c?.f() a warning saying Expression of type '()?' is unused is generated.

Resolved bug number: (SR-1752)

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[harlanhaskins]

@swift-ci please test

[lattner]

Thanks for working on this, but as the test runs above show, this causes a regression on the test suite.

[ahoppen]

I know, we just launched the CI in the lab to have a look at the test results and I didn't have time to update the tests yet. An update will follow in the next few days.

[ahoppen]

OK, I updated the tests and they should pass now.

try? in combination with a function returning Void will also no longer issue a warning as it was discussed in these swift-evolution threads: Original thread, my answer

This should simplify the rules on when a warning about an unused result is issued. Now such a warning should only be issued if the result type is not Void wrapped in any number of optionals and the called function is not marked as @discardableResult.

[ahoppen]

I resolved the merge conflicts that occurred because another test case was added to diagnostics.swift in 612991e

[CodaFi]

@ahoppen Looks like another conflict got introduced. Could you rebase again?

[ahoppen]

Once again the merge conflicts just resulted from another test being added to diagnostics.swift. I've resolved them now.

[CodaFi]

Thank you!

@swift-ci please test

[CodaFi]

macOS failures are unrelated to this patch.

Nice work @ahoppen 💥

[CodaFi]

Once more, with feeling!

@swift-ci please test and merge

[timbodeit]

Mailing list links are down.
They refer to the [swift-evolution] [Draft] Tuple-Based Compound Optional Binding thread.