Test in Swift 3 compatibility mode

[sharplet]

I think it would be ideal to add Nimble to the Swift 3 source compatibility suite. This PR should hopefully demonstrate that Nimble doesn't compile in Swift 3 compatibility mode. The two issues I've noticed:

• NSFastEnumerationIterator is a struct now, not a class
• The overload rules appear to have changed, and the tests don't compile due to ambiguous matcher overloads

I haven't deeply investigated the requirements for the source compatibility suite, but I wanted to kick of the discussion.

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Update!

Turns it's only a very minor change required to get -swift-version 3 working! I'm still not quick sure if we should merge with this change because of the warning under Swift 3, but I'm now successfully consuming Nimble from a Swift 4 project.

[sharplet]

@Quick/core Would love your input on whether to merge with this warning. If so, we could put out a patch release that supports Swift 4.

[pigeondotdev]

Please confirm. There's a warning with Swift 3 but everything is still compatible with Swift 3 and you have a working version for Swift 4? If so, LGTM (but I still recommend that we hear from a few others in the core team.

[modocache]

Sounds good, feel free to merge :)

[sharplet]

There's a warning with Swift 3 but everything is still compatible with Swift 3 and you have a working version for Swift 4?

That's correct. In Swift 3 this change generates a new warning (and infuriatingy a fixit), and under Swift 4 in compatibility mode compiles without any new warnings.

We may also need to add -swift-version 3 for this to compile in Xcode under Swift 4. I'll investigate this before merging.

[sharplet]

Ok, I've added the -swift-version 3 flag to the xcodeproj. Xcode made some automatic changes, so I committed those also.

Note: The tests don't compile under Swift 4 due to operator overload ambiguity. I don't know why, but it seems like maybe a Swift 3 compatibility bug? This also probably indicates that Swift 4 consumers won't be able to use certain operators right now, but at least compiling is a start!

[jeffh]

Thanks @sharplet!