Comparison of `Version`s also compares build metadata

[GoldsteinE]

Hi! This code:

use semver::Version;

fn main() {
    let a = Version::parse("0.0.0+a").unwrap();
    let b = Version::parse("0.0.0+b").unwrap();
    dbg!(a.cmp(&b));
}

currently prints

[src/main.rs:6] a.cmp(&b) = Less

According to SemVer 2.0.0 # 10, comparing versions should ignore build metadata. Including it in this comparison also create an inconsistency with VersionReq and makes cargo consider version change from 0.0.0+b to 0.0.0+a downgrading.

Crate documentation also suggests that implementation of Ord for BuildMetadata is only to allow comparing two BuildMetadata values and shouldn’t affect versions.

[dtolnay]

Ord worked the opposite way in versions 0.11 and older of this crate, and it was undesirable. See #108. Both behaviors are undesirable/confusing in different ways. I think my perspective agrees with #108 (comment): the spec says 0.0.0+a and 0.0.0+b have the same precedence for the purpose of selecting which versions satisfies a particular version req during version selection, but precedence is not the operation that cmp implements.

[GoldsteinE]

Should it be considered a bug in cargo then? I’d say that calling version change “downgrading” assumes that the new version has lower precedence (it’s also just generally weird, given that build metadata is often stuff like git commit hashes, which are not comparable).

[dtolnay]

I created rust-lang/cargo#12796 to change the message in Cargo.