[test] Version-guard some emoji tests.

[milseman]

Gate some emoji tests on a new enough iOS version.

rdar://problem/42139928

[milseman]

@swift-ci please test

[milseman]

CC @allevato

[swift-ci]

Build failed
Swift Test Linux Platform
Git Sha - d716e50ec65efc2f20d92c13213a7a149efd9391

[swift-ci]

Build failed
Swift Test OS X Platform
Git Sha - d716e50ec65efc2f20d92c13213a7a149efd9391

[allevato]

Should we gate the properties themselves with availability annotations instead of just the tests?

It really feels like bundling ICU with stdlib (as was discussed in SR-6076) is the only way to make sure we can safely roll things like this out on all platforms 😕

[milseman]

The properties are available, just the answers to queries can change with the version of Unicode. This is no different than say, String.count, which also changes with each new version of Unicode.

Separately, yes, bundling a version of ICU would help Linux. It wouldn't affect this change, as Darwin should use the system's ICU.

[milseman]

@swift-ci please test and merge

[allevato]

The properties are available, just the answers to queries can change with the version of Unicode. This is no different than say, String.count, which also changes with each new version of Unicode.

Ok, that's fair (the fact that we already have that issue with String.count, or with grapheme cluster breaking).

The fact that some of these properties are still unreliable depending on OS version still makes me a bit uncomfortable though, since I don't believe there's any obvious way for a user to map their platform/OS version to the version of Unicode that the system supports. One thing that came up during the proposal review was adding an API to the Unicode namespace that would let the user get the version triple of the Unicode that the system supported. Should we consider adding that so that the user has a trap door if they need fallback logic?

[milseman]

One thing that came up during the proposal review was adding an API to the Unicode namespace that would let the user get the version triple of the Unicode that the system supported. Should we consider adding that so that the user has a trap door if they need fallback logic?

Definintely!

[milseman]

@swift-ci please test and merge