Search code examples
rustrust-cargo

What is the difference between [dependencies] and [dev-dependencies]?

In a Cargo.toml manifest, what is the difference between the two types of dependencies? It seems that the "dev" dependency is conditional / invoked at a certain time only.

If I include a crate under [dev-dependencies] and try to use it in my code, it gives me an error:

[package]
# ... snipped ...

[dependencies]
# no uuid here

[dev-dependencies]
uuid = "1.0.0"

use uuid::Uuid;

fn main() {
    println!("Hello, world!");
}

error[E0432]: unresolved import `uuid`
 --> src/main.rs:1:5
  |
1 | use uuid::Uuid;
  |     ^^^^ use of undeclared crate or module `uuid`

But if I move it under [dependency], then there is no error. If the "dev" dependencies aren't used in my code, where are they used?

Solution

  • They are dependencies that only get included / built for examples, tests, and benchmarks. They will not be included when you run a simple cargo build.

    See development dependencies in the Cargo Book.