Usually, I only care to know about the version number of a crate when I'm going to add the crate to my Cargo.toml. In those cases, I use two extra Cargo subcommands from the cargo-edit project:

• cargo add — adds the current stable version of a crate to Cargo.toml. Options exist for allowing prerelease versions or marking it as a build / dev dependency.
• cargo upgrade — updates the version of a crate already in Cargo.toml. Similar to cargo update, but also changes Cargo.toml in addition to Cargo.lock.

As of Rust 1.41.0, you can use the following command to update crates to their latest version:

cargo install <crate>

This came from pull request #6798 (Add install-upgrade) and was stabilized in #7560 (Stabilize install-upgrade).

How does it work?

Instead of failing when cargo install detects a package is already installed, it will upgrade if the versions don't match, or do nothing (exit 0) if it is considered "up-to-date".

Forcing an upgrade / re-installation

The following command will always uninstall, download and compile the latest version of the crate - even if there's no newer version available. Under normal circumstances the install-upgrade feature should be preferred as it does save time and bandwidth if there's no new version of the crate.

cargo install --force <crate>

Documentation

Further information can be found in the GitHub issue rust-lang/cargo#6797 and in the official documentation chapter.

From the guide, rustup will check for updates to itself (in addition to the toolchain updates) every time you run rustup update. You could also exclusively update rustup by running rustup self update.

There is a optional subcommand cargo-update to do that:

cargo install cargo-update
cargo install-update -a

Done.

I've done this by creating a temporary cargo project and adding a small dependency to it. Something like this:

mkdir /tmp/deleteme \
    && cd /tmp/deleteme \
    && cargo init \
    && cargo add serde \
    && rm -rf /tmp/deleteme

You should immediately see the message:

Updating crates.io index