Intl.DateTimeFormat() returns short timeZoneName with GMT offset removed in some locales

[kueda]

Bug Description

Intl.DateTimeFormat() returns short timeZoneName with GMT offset removed in some locales.

• I have run gradle clean and confirmed this bug does not occur with JSC
• The issue is reproducible with the latest version of React Native.

Hermes git revision (if applicable):
React Native version: 0.77.0
OS: iOS 18.2.1
Platform (most likely one of arm64-v8a, armeabi-v7a, x86, x86_64): running on iPhone, so I guess one of the arm ones

Steps To Reproduce

Intl.DateTimeFormat(
  "en-GB",
  { timeZone: "Pacific/Honolulu", timeZoneName: "short" }
)
  .formatToParts( new Date( ) )
  .find( p => p.type === "timeZoneName" ).value

gives the following output

GMT

The Expected Behavior

GMT-10

FWIW, I see the correct output in Android 14, and by "correct" I mean the output I see in Firefox and Chrome, GMT-10 (I would expect it to be HST like it is in en-US, but an accurate offset seems preferable to an inaccurate short name).

I am pretty sure this is just due to formatToParts() behaving a bit differently. The - and 10 are in subsequent parts as literal and year elements. That's just not how the method behaves in a browser.

Related: marnusw/date-fns-tz#306

[neildhar]

Hey @kueda, the formatToParts implementation on iOS is unfortunately known to have major issues, which cannot easily be fixed. While we continue to provide it for backwards compatibility, we advise against using it for now.