docs.rs homepage examples use `rand_core` crate option, but do not mention its existence

[samuela]

I'm attempting to follow the documentation and have the following file:

use ed25519_dalek::SigningKey;
use rand::rngs::OsRng;

fn main() {
  let mut csprng = OsRng;
  let signing_key: SigningKey = SigningKey::generate(&mut csprng);
}

which I'm attempting to build against ed25519_dalek 2.1.1 and rand 0.8.5 but I'm getting the following error:

error[E0599]: no function or associated item named `generate` found for struct `SigningKey` in the current scope
 --> src/bin/foo.rs:6:45
  |
6 |   let signing_key: SigningKey = SigningKey::generate(&mut csprng);
  |                                             ^^^^^^^^ function or associated item not found in `SigningKey`

For more information about this error, try `rustc --explain E0599`.
error: could not compile `cherami` (bin "foo") due to previous error

[tarcieri]

I agree that example is deficient and doesn't fully explain everything you need to do for the generate method to be available.

For more information, see the documentation here, note "available on crate feature rand_core only":

https://docs.rs/ed25519-dalek/latest/ed25519_dalek/struct.SigningKey.html#method.generate

Solution: you need to enable the rand_core crate feature in Cargo.toml:

[dependencies]
ed25519-dalek = { version = "2", features = ["rand_core"] }

[samuela]

Thanks @tarcieri ! That indeed solves the compilation error. I was not aware of the rand_core option after reading https://docs.rs/ed25519-dalek/latest/ed25519_dalek/.

I will update the issue title to reflect a docs issue, instead of a compilation one.