confusing deprecation notice for chrono::TimeZone::datetime_from_str

[decathorpe]

I'm regularly using something like Utc.datetime_from_str(foo, "%Y-%m-%d %H:%M") in my projects to parse timestamps into a Datetime<Utc>, and I'm now getting deprecation warnings for that.

I tried replacing those calls with DateTime::parse_from_str as it's documented in the deprecation warning - but that returns a Datetime<FixedOffset>, and I do not see a way to convert a Datetime<FixedOffset> into a Datetime<Utc> (at least no obvious ones), so it is not a direct replacement. Reading the documentation, I'm also unsure whether it's even semantically equivalent.

Changing the type of any parsed timestamps to Datetime<FixedOffset> everywhere would be a pretty tedious ... is there a way to convert a Datetime<FixedOffset> to a Datetime<Utc> to get back the previous return type?

[jtmoon79]

convert a Datetime<FixedOffset> to a Datetime<Utc>

Can you use the From trait?

    let dtfo: DateTime<FixedOffset> = DateTime::parse_from_str("19700102T23:55:55+00", "%Y%m%dT%H:%M:%S%#z").unwrap();
    let dtutc: DateTime<Utc> = DateTime::<Utc>::from(dtfo);

[decathorpe]

hum ... from the docs for DateTime::parse_from_str:

Note that this method requires a timezone in the input string.

My input string does not have a timezone, but I know that it's a UTC timestamp.

So should I use a NaiveDateTime? But From<NaiveDateTime> is not implemented for DateTime<Utc>.

[decathorpe]

Indeed, using Datetime::parse_from_str is not possible with the format I have, I get: "input is not enough for unique date and time"

[pitdicker]

You probably want to parse the input as a NaiveDateTime. That is the closest type to your input, because the timezone information ('UTC') is not part of the input but something you add to it. Code:

NaiveDateTime::parse_from_str(foo, "%Y-%m-%d %H:%M").unwrap().and_utc();

[decathorpe]

Yup, this works, thank you!

Maybe the deprecation warning could mention both DateTime::parse_from_str and NaiveDateTime::parse_from_str then? It looks like the former is only a replacement if the format has specified a timezone, and the latter needs to be used if the timezone is not part of the format.

[pitdicker]

It does since 0.4.32, released two days ago (see #1342) 😄.

[decathorpe]

Ah! Thank you. I probably did not notice because 0.4.32 failed to build on docs.rs.