Does `extern crate` serve any purpose in the 2021 edition?

[jacg]

Are there any situations where extern crate needs no be used in the 2021 (or 2018) edition, or is it there purely for backwards compatibility?

[jbe]

See:

Usage of `extern crate`?

Hello guys! I'm currently trying to understand the usage of extern crate. The rust-reference rust-reference says: An extern crate declaration specifies a dependency on an external crate. (...) So is it like adding a new dependency by adding it to Cargo.toml? What are its usages? If I understood it correctly, it just brings the given crate into our current scope, so we can write use theCrate::stuff; for example. Also according to this Stack Overflow and ticked answer it looks like that it s…

(click here to see full thread)

[juggle-tux]

extern crate is still useful if you want to import all macros from a crate like

#[macro_use] // to bring `anyhow!`, `bail!` and `ensure!` into scope
extern crate Anyhow;

[chrefr]

I would not recommend that. It's much less clear than use, and an artifact of old system.

[CAD97]

As in the other thread, extern crate alloc; is one use, as is #![no_std] #[cfg(feature = "std")] extern crate std;.

One use that I don't see often mentioned is extern crate self as name, which allows you to use ::name in addition to ::crate to refer to your own crate. This can be useful for e.g. macros, or even just for making internal code look more like external code.