Add support for .withFractionalSeconds to ISO8601DateFormatter.

[armadsen]

This fixes SR-7079.

[pushkarnk]

@swift-ci please test

[millenomi]

On behalf of @parkera, approved.

[millenomi]

Per @spevans: this patch may fail on Ubuntu 14.04 because of libicu version mismatches. (cc @parkera.)

I'm going to veto it for now, but it's only until we can figure out how to version things so that we can pipe through the ICU version and make it conditionally available.

[armadsen]

Thanks everyone. I'd be happy to work on the underlying issue of making it conditional on a new-enough underlying ICU version.

[parkera]

Is there a macro defined by ICU that we could use to conditionally compile this in?

[millenomi]

Yes, but we have to pipe it through to the Swift build somehow.

[spevans]

ICU defines U_ICU_VERSION_MAJOR_NUM (52 on 14.04, 55 on 16.04) so this could be used to set a #define in ForSwiftFoundationOnly.h. I suggested something similar in #1522 (comment)

[millenomi]

I've done some sleuthing.

As far as I can see:

• Ubuntu 14.04 ships with ICU 52.1
• macOS 10.12 ships with ICU 57.1
• macOS 10.13 ships with ICU 59.1
• We only support this as API on 10.13
• Ubuntu 16.04 ships with ICU 55.1
• The PR builder currently runs on 16.04 and tests pass.

[millenomi]

My next step is to run DarwinCompat and see if the new tests pass on Darwin as well. If they do, it means 16.04 supports at least as much as Darwin.

[millenomi]

(or is a strong signal to that effect.)

[millenomi]

If someone could run tests here and check they pass on 14.04, it'd eliminate ambiguity. But I don't have a 14.04 box handy.

[millenomi]

To be clear: it looks like 14.04 (ICU 52.1) has support for the S modifier in dtfmtsym.cpp much like later versions. It's only behavior differences that concern me.

[spevans]

For completeness, Ubuntu 18.04 ships with 60.2

[millenomi]

I decided to just set up a 14.04 VM, see if tests run there, and if so just introduce the API.

[millenomi]

Tests pass locally on 14.04.

millenomi@ubuntu1404:/media/millenomi/Sources/swift-corelibs-foundation$ LD_LIBRARY_PATH=/media/millenomi/Sources/build/Ninja-RelWithDebInfoAssert/foundation-linux-x86_64/Foundation/:/media/millenomi/Sources/build/Ninja-RelWithDebInfoAssert/xctest-linux-x86_64:/media/millenomi/Sources/build/Ninja-RelWithDebInfoAssert/libdispatch-linux-x86_64/src/.libs: ../build/Ninja-RelWithDebInfoAssert/foundation-linux-x86_64/TestFoundation/TestFoundation
Test Suite 'All tests' started at 2018-06-11 01:41:45.261
…
Test Suite 'All tests' passed at 2018-06-11 01:42:11.334
	 Executed 1330 tests, with 0 failures (0 unexpected) in 25.85 (25.85) seconds

millenomi@ubuntu1404:/media/millenomi/Sources/swift-corelibs-foundation$ LD_LIBRARY_PATH=/media/millenomi/Sources/build/Ninja-RelWithDebInfoAssert/foundation-linux-x86_64/Foundation/:/media/millenomi/Sources/build/Ninja-RelWithDebInfoAssert/xctest-linux-x86_64:/media/millenomi/Sources/build/Ninja-RelWithDebInfoAssert/libdispatch-linux-x86_64/src/.libs: ../build/Ninja-RelWithDebInfoAssert/foundation-linux-x86_64/TestFoundation/TestFoundation TestFoundation.TestISO8601DateFormatter
Test Suite 'Selected tests' started at 2018-06-11 01:42:48.748
Test Suite 'TestISO8601DateFormatter' started at 2018-06-11 01:42:48.752
Test Case 'TestISO8601DateFormatter.test_stringFromDate' started at 2018-06-11 01:42:48.752
Test Case 'TestISO8601DateFormatter.test_stringFromDate' passed (0.022 seconds)
Test Case 'TestISO8601DateFormatter.test_dateFromString' started at 2018-06-11 01:42:48.774
Test Case 'TestISO8601DateFormatter.test_dateFromString' passed (0.001 seconds)
Test Case 'TestISO8601DateFormatter.test_stringFromDateClass' started at 2018-06-11 01:42:48.775
Test Case 'TestISO8601DateFormatter.test_stringFromDateClass' passed (0.015 seconds)
Test Suite 'TestISO8601DateFormatter' passed at 2018-06-11 01:42:48.791
	 Executed 3 tests, with 0 failures (0 unexpected) in 0.038 (0.038) seconds
Test Suite 'Selected tests' passed at 2018-06-11 01:42:48.791
	 Executed 3 tests, with 0 failures (0 unexpected) in 0.038 (0.038) seconds

millenomi@ubuntu1404:/media/millenomi/Sources/swift-corelibs-foundation$ uname -a
Linux ubuntu1404 4.4.0-31-generic #50~14.04.1-Ubuntu SMP Wed Jul 13 01:07:32 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux

[armadsen]

Thanks for your work on this @millenomi, and thanks for the help getting it put together, @pushkarnk!