How to identify if a generic `DateTime<Tz>` is in a DST transition?

[davidhewitt]

How to identify if a generic `DateTime` is in a DST transition?

from chrono.

[pitdicker]

That is mostly it. However, LocalResult::Ambiguous is only returned if a transition creates a fold (clock is moved backward), and LocalResult::None when the transition crates a gap (clock is moved forward).

The shortest way to write this is using LocalResult::single():

let is_dst_folded = dt.naive_local().and_local_offset(dt.offset).single().is_none();

Note that we sometimes rely on platform functions to convert to DateTime<Local>. On Windows and wasm the platform function always returns a single value, so we can't return anything but LocalResult::Single there yet.

And also unfortunately an error in the platform function makes us return LocalResult::None, just like during a transition gap :-(. But if you use something like chrono_tz which is fully under our control, this method works.

[davidhewitt]

Thanks for the confirmation. 👍