Marking this as a StarterBug – the issue has to do with the overload types we assign to the declarations, from the function ValueDecl::getOverloadSignatureType() in Decl.cpp. For functions we use mapSignatureFunctionType in order to strip away things like @escaping for the purposes of redeclaration checking. We should ideally also be using this for subscripts.

Note that this is a source breaking change so would need to be guarded by a isSwiftVersionAtLeast check.

It's not that source breaking. It's unlikely anyone relies on this.

Comment by Frederick Kellison-Linn (JIRA)

Does that mean you don’t think it needs to be version-guarded?

If no one has started work on this yet I’d be happy to take it on.

I would always err on the side of simplicity. Run source compat tests first of course. We can always version-guard it later if we ship a public release with the change and people complain.

I think its rare to have subscripts take functions, period; overloading on escaping-ness is even more rare.

@slavapestov Fair enough – my main concerns were that subscripts with function parameters can come up with autoclosures, and that changing the overload signature type also affects cross-module shadowing. I do agree that it's very unlikely anyone is relying on overloading on escaping-ness though.

Comment by Frederick Kellison-Linn (JIRA)

Hey @xedin—just wanted to give you a heads up that I put a PR up for this issue here: #23457

Don't want you to waste time duplicating work! Sorry about that, should have assigned this bug to myself.

Thanks for letting me know!