Gem version

Implement Ruby's Gem::Version comparison logic in Rust.

See also: Gem::Version tests

The main use case is for the Heroku Ruby buildpack https://github.com/heroku/buildpacks-ruby and associated ecosystem of managing Ruby logic inside of Rust.

Install

Add it to your Cargo.toml:

$ cargo add gem_version

Use

use std::str::FromStr;
use gem_version::GemVersion;

let version = GemVersion::from_str("1.0.0").unwrap();
assert!(version < GemVersion::from_str("2.0.0").unwrap());

Diverging behavior

Ruby's Gem::Version reference implementation converts - to .pre. (commit). This means the value you put in is not the value you get out:

puts Gem::Version.new("1.0.0-alpha1")
# => "1.0.0.pre.alpha1"

It seems the coupling between comparison logic and representation was accidental at the time of introduction. This library diverges by showing the original string (and decoupling that from the comparison representation):

use std::str::FromStr;
use gem_version::GemVersion;

let version = GemVersion::from_str("1.0.0-alpha1").unwrap();

// Version does not have `.pre.` in it:
assert_eq!("1.0.0-alpha1", &version.to_string());

// But it performs comparisons as if it did:
assert_eq!(
    GemVersion::from_str("1.0.0.pre.alpha1").unwrap(),
    version
);

If you want the upstream (reference) behavior that also changes the display output, you can make a newtype that uses replace("-", ".pre.") on the input String.