rustdoc: Show package version in the generated documentation when invoked through cargo doc

[crumblingstatue]

It would be useful for users to know for which version of a package they are reading the documentation for.

This would be especially helpful in identifying outdated documentation online, which there is an abundance of.

Moved from rust-lang/rust#29275 due to request.

[alexcrichton]

Does rustdoc have the ability to do this? AFAIK we'd need to expose a flag to rustdoc first.

[crumblingstatue]

I don't think rustdoc has the ability to do this, which is why I opened this issue at rust-lang/rust, but @steveklabnik closed the issue there, requesting it to be moved here.

[alexcrichton]

Ok... well it's at least a todo item here!

[steveklabnik]

I thought rustdoc had the ability to control output directly already; in the end, even if rustdoc needs some support, it will need cargo to actually do the right thing here, since rustdoc can't know version info.

[ehuss]

This has been implemented, stabilization is tracked in #7907.