`TimeZone` rounds second-offset unlike DarwinFoundation.

[YOCKOW]

The code below says all.

import Foundation

print(TimeZone(secondsFromGMT: 15)!.secondsFromGMT())
// Prints "15" with DarwinFoundation
// Prints  "0" with swift-corelibs-foundation

print(TimeZone(secondsFromGMT: 3690)!.secondsFromGMT())
// Prints "3690" with DarwinFoundation
// Prints "3720" with swift-corelibs-foundation

Environment
Swift version 6.0-dev (LLVM 57177aa1b91540b, Swift 8be62863326595c)
Target: x86_64-unknown-linux-gnu

[parkera]

On the macOS 15 Beta (which shares the same TimeZone implementation as Swift 6.0), I see these results:

  1> import Foundation
  2> print(TimeZone(secondsFromGMT: 15)!.secondsFromGMT())
15
  3> print(TimeZone(secondsFromGMT: 3690)!.secondsFromGMT())
3690

On the Ubuntu Swift 6 nightly snapshot from 8/22 I see these results:

  1> import Foundation
  2> print(TimeZone(secondsFromGMT: 15)!.secondsFromGMT())
15
  3> print(TimeZone(secondsFromGMT: 3690)!.secondsFromGMT())
3690

[parkera]

swift-6.0-DEVELOPMENT-SNAPSHOT-2024-08-22-a

[parkera]

So in other words, I can't reproduce the swift-corelibs-foundation result above. Is that from a previous release of Swift?

[YOCKOW]

Is that from a previous release of Swift?

I’m sorry, but Swift which produced that result seems a little old. I confirmed that FoundationEssentials doesn’t have such a bug. I mean it is probably corelibs-foundation specific.

[parkera]

The test case above is using swift-corelibs-foundation (which re-exports FoundationEssentials' TimeZone type as of 6.0).

[YOCKOW]

Hmm🤔
There may be some other factors affecting this issue.
I'm going to try more investigation.

[YOCKOW]

Toolchain (Ubuntu 22.04)	This issue
5.10.1	🪰 exists
swift-5.10-DEVELOPMENT-SNAPSHOT-2024-05-31-a	🪰 exists
swift-6.0-DEVELOPMENT-SNAPSHOT-2024-07-19-a	🪰 exists
swift-6.0-DEVELOPMENT-SNAPSHOT-2024-07-21-a	✅ no problem
swift-DEVELOPMENT-SNAPSHOT-2024-07-15-a	🪰 exists
swift-DEVELOPMENT-SNAPSHOT-2024-07-22-a	✅ no problem

I wonder what happened around 20th July.

[parkera]

That is when we merged the re-core into the 6.0 branch.

#5011