feat: bootstrap sqlx-jiff development

[tisonkun]

This refers to #50.

Firstly, I considered to add a separated sqlx-jiff method, but soon I found that due to Rust's orphan rules, implementing sqlx's trait for Timestamp and other types requires the code to be located at the same crate (jiff). Otherwise we need an extra wrapper struct like:

#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
pub struct Timestamp(pub jiff::Timestamp);

I prefer to implement code in jiff and gate it with feature flags.

@BurntSushi This demonstrates the integration implementation direction. I'll complete other parts when we agree on this direction.

[BurntSushi]

#50 (comment) discusses this. And the orphan rule is taken into account there. The way to do this integration, short of getting it merged upstream in sqlx itself, is with a wrapper type in a jiff-sqlx crate. The comment linked explains how to do this.

Jiff is a "low level" crate. Having it depend on "high level" crates like sqlx would lead to all sorts of problems, especially if and when the time ever comes for sqlx to add Jiff integration on their end. It's really a non-starter.

[tisonkun]

@BurntSushi Yeah .. Adopt the other way now.

[tisonkun]

impl AsRef also?

[BurntSushi]

I'm not sure how far we want to go here. In theory, there are a lot of different traits we might want to implement. In practice, I'm not sure how useful they all are or whether we even want to encourage their use. I'd start with a minimal useful set for now.

I'm actually not even sure about using Deref here. I'd leave that out for now.

[tisonkun]

OK. Then I'd revoke #[derive(PartialEq, Eq, Serialize, Deserialize)] also but just make it an opaque wrapper type. Users should always call to_jiff and use jiff::Timestamp's method.

[BurntSushi]

Also, the crate should be called jiff-sqlx, since it lives with jiff.

[tisonkun]

Other type mapping to be wrapped once we agree on the pattern:

• jiff::civil::Date <-> DATE
• jiff::civil:Time <-> TIME
• jiff:civil::DateTime <-> TIMESTAMP
• jiff::Timestamp <-> TIMESTAMPTZ
• jiff::SignedDuration <-> INTERVAL

Ref -

• feat: support jiff integration for postgresql launchbadge/sqlx#3511
• Add Jiff support sfackler/rust-postgres#1164