Support for parsing/formatting as RFC-3339 with Serde

[sazzer]

Issue #232 has added support for parsing and formatting timestamps using the RFC-3339. However, as best as I can tell, it only supports this in explicit code. It would be useful if this was supported in the Serde feature as well.

For example, instead of needing to do:

#[derive(Serialize)]
struct SomeResponse {
    pub some_timestamp: String
}
.....
SomeResponse {
    some_timestamp: value.format(time::Format::Rfc3339).expect("Failed to format value")
}

I could just do:

#[derive(Serialize)]
struct SomeResponse {
    #[serde(with = "time::serde::rfc3339")]
    pub some_timestamp: OffsetDateTime
}
.....
SomeResponse {
    some_timestamp: value
}

[jhpratt]

Yeah, this is doable.

[jhpratt]

This should be completed (sans tests) on the serde-rfc3339 branch. I will not be releasing this until weak feature dependencies has been on stable for the requisite amount of time, as doing so would mean anyone using a fair number of APIs would pull in serde for no apparent reason.

[mzabaluev]

as doing so would mean anyone using a fair number of APIs would pull in serde for no apparent reason.

I'm not sure I understand the concern here. The whole mod serde is gated by the serde feature, use of time::serde::rfc3339 further needs parsing and formatting, hence std (note this could be eased to alloc by #400). But anyone using this helper module must be needing serde anyway, aren't they?

[jhpratt]

I have a plan to get this to work. I am just working on something else first.

[jhpratt]

I thought about putting this behind the serde-human-readable flag, but that would require the default serialization to be human readable just to support the attributes. As a result, I decided to put this behind a new serde-well-known feature flag.

This is on main now — both RFC3339 and RFC2822. Tests will be added for this soon.

[George-Miao]

Hi! Are serde-well-known available on crates.io now?

[jhpratt]

Not yet, no. It was just merged recently. There be a release soon-ish once some other changes get finalized.