How to idiomatically alias a crate in Rust 2018?

The idiomatic solution is to rename the crate in Cargo.toml. See the answer by Tim Diekmann for more information about that.

But if you don't want to use Cargo.toml renaming for some reason, you can still use the old syntax. It's soft-deprecated, but not removed. So this still works:

extern crate foo_sys as foo;

(Playground example)

This can be achieved with the rename-dependency Cargo feature, available in Rust 1.31. With this feature, it's possible to provide a package attribute to the dependencies:

The rename-dependency feature allows you to import a dependency with a different name from the source. This can be useful in a few scenarios:

• Depending on crates with the same name from different registries.
• Depending on multiple versions of a crate.
• Avoid needing extern crate foo as bar in Rust source.

Instead of writing

[dependencies]
foo_sys = "0.2"

the package key can be added to the dependency in Cargo.toml:

[dependencies]
foo = { package = "foo_sys", version = "0.2" }

WARNING: Cargo prior to Rust 1.26.0 may download the wrong dependency when using this feature!