Implement serde Serialize/Deserialize for VersionReq

[brson]

Only when the "serde" feature is enabled. It's implemented for Version but not VersionReq. I imagine this wants a custom serializer, not a derived one. Maybe @steveklabnik you can say more about how this should be implemented and tag it help wanted.

[steveklabnik]

I'm not sure what the use-case is, so I'm not sure why it'd want to be custom.

[brson]

This is a type with a natural string form, so I thought it might want to be serialized in that form - for comparison, Version uses a custom serializer.

A contributor can probably start out with derived serialization and hash it out on the PR.

[brson]

Oh, actually, my use case was to deserialize version requirements from the crates.io API into a VersionReq. I presume that would require a custom serializer / deserializer, but don't know for sure. In the crates.io API they are just strings that are shaped like version requirements.

[steveklabnik]

Yeah I mean, one problem with VersionReq generally is that there's no "normal form" for them; that is, you could construct two different VersionReqs with different constraints that result in the same set of versions, so they wouldn't be equal to each other anymore... I'm wondering if that's an issue with serialization.

Maybe trying out the default one and seeing if it works for crates.io is the right call.

[KodrAus]

Is this all sorted now?

[opilar]

Seems it's already in release 0.8.0. Should be ok.

[valarauca]

As of 0.9.0 this does not appear to work

Edit:

semver = { version = "0.9.0", features = ["serde"] }

that works. Had to read the Cargo.toml to figure it out.

[dtolnay]

This was implemented in #122.