Inconsistent Time Zone Formatting Between macOS and Static Linux SDK

[barnard-b]

When formatting a date with the EST time zone on macOS and the Static Linux SDK, the resulting date string is inconsistent between the two platforms.

macOS

Resolved Time Zone for EST is EST
It is now Thursday, October 10, 2024 at 3:32:23 PM GMT-05:00

Linux

Resolved Time Zone for EST is EST
It is now Thursday, October 10, 2024 at 4:32:23 PM Eastern Daylight Time

---

Swift: Apple Swift version 6.0.1 (swift-6.0.1-RELEASE) Target: arm64-apple-macosx15.0
Static Linux SDK: swift-6.0.1-RELEASE_static-linux-0.0.1
macOS: 15.0.1
Linux: Alma Linux 8.10

FoundationTest.swift

import Foundation

@main
struct App {
    static func main() async throws {
        let date = Date()
        let identifier = "EST"
        let timeZone = TimeZone(identifier: identifier)
        print("Resolved Time Zone for \(identifier) is " + (timeZone?.identifier ?? "Invalid"))
        
        let formatter = DateFormatter()
        formatter.locale = Locale(identifier: "en_US_POSIX")
        formatter.timeZone = timeZone
        formatter.dateStyle = .full
        formatter.timeStyle = .full
        
        let formatted = formatter.string(from: date)
        print("It is now \(formatted)")
    }
}

Package.swift

// swift-tools-version: 6.0

import PackageDescription

let package = Package(
    name: "FoundationTest",
    platforms: [
        .macOS(.v12)
    ],
    targets: [
        .executableTarget(name: "FoundationTest")
    ]
)

Build for Linux

xcrun --toolchain swift swift build --swift-sdk x86_64-swift-linux-musl

Build for macOS

xcrun --toolchain swift swift build

[itingliu]

There seems to be two separate issues here:

1. A bug in Linux, where you've set the timezone to be EST, but the output is in EDT.
2. Inconsistent behavior of the time zone representation: Linux is using the timezone identifier, but mac is using GMT offset. I think the full name is the expected behavior.

I do want to point out that this isn't 100% correct...

let identifier = "EST"
let timeZone = TimeZone(identifier: identifier)

"EST" isn't a valid time zone identifier. It's an abbreviation, so you should be using the other API, which reverse-look up the appropriate identifier for you

let timeZone = TimeZone(abbreviation:"EST") 

Using this would solve (2) and format EST as its full name.