[stdlib] Set, Dictionary: Fix (cocoa, native) equatable implementation

[AndrewSB]

I was looking through the implementation of set and this change felt off to me.

@lorentey it looks like you changed this last, what do you think?

[lorentey]

I was knee deep in Set guts trying to figure out how this managed to remain undetected for so long, but it turns out the original code is correct! Unlike the rest of the cases, here isEqual(to:) is called on rhs, not lhs. (_CocoaSet.isEqual(to:) does not support a native argument, so this line wouldn't compile with the suggested change.)

This is way too subtle. I blame the terrible naming convention lhs and rhs -- naming these parameters left and right would've highlighted the swap much better. Would you like to rename them?

[AndrewSB]

oh! I see, in this case the lhs and rhswere reversed! The naming does make it hard to notice that. Let me reorder them instead, sorry for the false alarm

[AndrewSB]

@lorentey I think this is ready for another pass & potentially to be merged

[lorentey]

@AndrewSB The current version won't work, either, for the same reason I wrote above:

_CocoaSet.isEqual(to:) does not support a native argument, so this line wouldn't compile with the suggested change.

Stepping back, what concrete problem are you addressing with this PR? Have you verified that your change builds & runs locally before submitting this for review?

[lorentey]

@swift-ci smoke test

[lorentey]

13:34:51 
/Users/buildnode/jenkins/workspace/swift-PR-osx-smoke-test/branch-master/swift/stdlib/public/core/Dictionary.swift:1585:60: error: cannot convert value of type '_NativeDictionary<Key, Value>' to expected argument type '__CocoaDictionary'
13:34:51       return lhs._variant.asCocoa.isEqual(to: rhs._variant.asNative)
13:34:51                                                            ^
13:34:51 /Users/buildnode/jenkins/workspace/swift-PR-osx-smoke-test/branch-master/swift/stdlib/public/core/Set.swift:418:60: error: cannot convert value of type '_NativeSet<Element>' to expected argument type '__CocoaSet'
13:34:51       return lhs._variant.asCocoa.isEqual(to: rhs._variant.asNative)
13:34:51                                                            ^

[gribozavr]

Assuming there is a bug in this code that this PR fixes, please add tests for it -- thanks!

[lorentey]

@AndrewSB I'm closing this as it isn't building in this stage, and I don't see what problem these changes are addressing. Feel free to submit a new PR if there is an issue to be resolved.