Implement RFC 2052: Epoches

[Manishearth]

Todo:

• Make epoches affect the fingerprint
• Tests

cc rust-lang/rust#44581

Rust PR: rust-lang/rust#48014

r? @acrichto

[alexcrichton]

Thanks! Could some tests be added as well? Something like:

• A test to ensure it's unstable
• A test for a malformed epoch key
• A test that we pass the right epoch
• A test that we unconditionally pass the epoch

[withoutboats]

I think it would be more user-friendly to call the field in the toml rust. While we've talked about the idea among contributors in terms of "epochs," I think in terms of marketing these releases we will not emphasize the "epoch" language. Among the broader user base and potential use base, this will just be known as "Rust 2018."

If/when we grow the ability to specify a particular toolchain version (e.g. rustc-1.25.0), that should be called toolchain.

[package]
name = "failure"
version = "1.2.0"
rust = "2018"
toolchain = "1.31.0"

[withoutboats]

Cute, but isn't the only effect of this to make this enum a u16?

[Manishearth]

It's more there for forcing the PartialOrd to be the right order. But it's not necessary for Cargo; I just copied this definition from the Rust PR (where comparing epochs is more important)

[Manishearth]

Yeah, was writing the tests on the flight. Pushing now, will add the other tests you mentioned too.

[Manishearth]

Pushed up the tests.

Note that right now it demands a string key, epoch = "2015". epoch = 2015 will not work. I'm opting for a string in case in the future we wish to do unstable epoch release candidates via epoch = "2018-next" or whatever. Or even epoch = "2018-second" if for some reason we do two epochs in a year. However I'm not sure how to tell Serde to accept integer keys and turn them into strings.

Regarding the outward facing name of the feature, @aturon, thoughts?

(it's unstable so we don't need to decide this immediately, but there's also no rush on landing this anyway)

[withoutboats]

We tend to require strings even when integers could suffice; we don't accept a version number of 1 for example, it would have to be "1".

[Manishearth]

wfm. Though I think not allowing 2015 would be a bit surprising

[alexcrichton]

@Manishearth wanna switch to rust and we can land this on nightly?

[Manishearth]

Done

[alexcrichton]

@bors: r+

[bors]

📌 Commit 270f6e2 has been approved by alexcrichton

[bors]

⌛ Testing commit 270f6e2 with merge 750df0a...

[bors]

☀️ Test successful - status-appveyor, status-travis
Approved by: alexcrichton
Pushing 750df0a to master...

[bjorn3]

Missing trailing newline