The Output of DateTime.ToString() is different in MacOs 14 from other platforms

[msJinLei]

Description

The format string of DateTime.ToString misses one space in MacOs-14 compared to other platforms, even if I specify culture info explicitly.

Reproduction Steps

Code

                if (obj is DateTime dateTime)
                {
                    sb.AppendLine(dateTime.ToString("G", new CultureInfo("en-US")));
                }
                else
                {
                    sb.AppendLine(obj.ToString());
                }

Run on the following environment

• Runner Image
  • Image: macos-14
  • Version: 20241007.165
  • Included Software: https://github.com/actions/runner-images/blob/macos-14/20241007.165/images/macos/macos-14-Readme.md
  • Image Release: https://github.com/actions/runner-images/releases/tag/macos-14%2F20241007.165
• SDK Version: 6.0.427

Expected behavior

6/7/2017 10:54:00 PM

Actual behavior

6/7/2017 10:54:00PM

Regression?

No response

Known Workarounds

No response

Configuration

No response

Other information

No response

[dotnet-policy-service]

Tagging subscribers to this area: @dotnet/area-system-globalization
See info in area-owners.md if you want to be subscribed.

[huoyaoyuan]

Duplicate of #102220, #103750, and #107842 .

The globalization format is provided by Unicode standard and shipped with underlying OS, and it does change from version to version. App code should not expect them being invariant.

[DL444]

The only culture that is guaranteed to be invariant is InvariantCulture, hence the name.

[Clockwork-Muse]

If you're writing a user-facing application and field (as seems likely on macOS), then format according to the user UI culture and present whatever it gives you without otherwise inspecting or modifying it.
If you're writing a field for persistence or interchange (which seems somewhat more likely given the example code) then you must use the invariant culture (and usually one of the roundtrip formats).

My personal recommendation is to never rely on the ambient culture - that is, always explicitly pass in the relevant culture to ToString() calls. This can help you keep track of what you're using that data for.