[SE-0211] Emoji properties require ICU 57 or later

[benrimmington]

Availability of emoji properties should be platform versions which have a /usr/lib/libicucore.dylib derived from ICU 57 or later.

ICU	macOS	iOS	tvOS	watchOS
55	10.11	9	9	2
57	10.12	10	10	3
59	10.13	11	11	4

These platform versions are based on the unicode/uchar.h and unicode/uvernum.h headers of:

• the macOS ICU projects at https://opensource.apple.com/;
• the iOS, tvOS, and watchOS SDKs.

(I didn't check as far back as macOS 10.9 or iOS 7).

This pull request is a follow-up to:

• b454e8d
• [test] Version-guard some emoji tests. #17992

[benrimmington]

Cc: @allevato @milseman

[allevato]

When I last brought this up, @milseman in this comment felt that the properties shouldn't be gated with availability annotations in this comment.

Reading over it again, I probably disagree with the first sentence "The properties are available"; before the version of ICU that implemented the corresponding version of the standard, the properties aren't available, and there's no way to use them on an older OS that produces the right result. That's distinct from the grapheme cluster behavior alluded to in String.count, where the concept exists but its behavior changes.

But I'd like to hear if Michael has any other concerns about this.

Sadly for Linux, there's no way to gate the properties based on version there, but that's ok, because the long-term solution is to bundle ICU with stdlib to ensure that it always contains what we need.

[milseman]

Right, if the API isn't even available, then we need to disable it on that platform version. IIRC, I was referring to properties that were available but gave a different answer than what we were testing for.

[allevato]

I regret not being clearer then in my original comment on the other PR. 🙂 In that case, I agree completely—let's do this, because the properties don't exist at all on the OS versions before those listed above.

[milseman]

Minor test change requested, LGTM

[milseman]

@swift-ci please test and merge

[benrimmington]

• Build #1196: Automatically restarting the build, due to invalid sha
• Build #1198: ERROR: Couldn't find any revision to build. Verify the repository and branch configuration for this job.

[jrose-apple]

@swift-ci Please test

[swift-ci]

Build failed
Swift Test OS X Platform
Git Sha - ef1a6a4b7f4ddaba72b18b978266fce32b6277ed

[swift-ci]

Build failed
Swift Test Linux Platform
Git Sha - ef1a6a4b7f4ddaba72b18b978266fce32b6277ed

[benrimmington]

This is ready to merge (all checks have passed).