On key-generation example (documentation), "rand" should be "rand-std" instead

[vinliao]

I copy-pasted the key-generation example written on the documentation, but it didn't work. It only worked when I used the feature rand-std instead of rand.

To reproduce, boot up a new Rust project, and add this to main.rs:

use secp256k1::rand::rngs::OsRng;
use secp256k1::{Secp256k1, Message};
use secp256k1::hashes::sha256;

let secp = Secp256k1::new();
let mut rng = OsRng::new().expect("OsRng");
let (secret_key, public_key) = secp.generate_keypair(&mut rng);
let message = Message::from_hashed_data::<sha256::Hash>("Hello World!".as_bytes());

let sig = secp.sign_ecdsa(&message, &secret_key);
assert!(secp.verify_ecdsa(&message, &sig, &public_key).is_ok());

Using this dependencies causes error: secp256k1 = {version="0.21.2", features=["rand", "bitcoin_hashes"]}. After replacing rand with rand-std, it works.

[apoelstra]

ACK 2732891

Yeah, I think OsRng requires std. That's unfortunate.

[tcharding]

Thanks for the PR! I actually went to verify this just recently, clearly I should have trusted the code not the docs :) For rand 0.6.5 (which we currently use) the docs for OsRng do not say that std features is needed.

Thanks again.

https://docs.rs/rand/0.6.5/rand/rngs/struct.OsRng.html

tACK 2732891

[vinliao]

I've found a few "rand" feature requirement in the documentation and have replaced it with "rand-std" (again).

[apoelstra]

I don't understand why rand-std is needed for any of these new ones. Can you confirm that they don't work with rand?

[vinliao]

That last commit was not a well-considered commit. I was browsing the documentation and just sort of assumed that it needed to be changed (because it had rand instead of rand-std in it). It was a mistake on my part. I have removed the last commit from the PR.

[tcharding]

Don't feel bad for getting confused @vinliao, I recently got merged a heap of rustdoc tests that should fail because I used feature-gate rand instead of rand-std :(

EDIT:

Seems there is a bug in cargo, the tests in key.rs currently on master branch run successfully but AFAICT they should fail. Here is an example, running cargo test --features=rand should make this test fail but it doesn't?

/// Secret 256-bit key used as `x` in an ECDSA signature.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// # #[cfg(all(feature = "rand", any(feature =  "alloc", feature = "std")))] {
/// use secp256k1::{rand, Secp256k1, SecretKey};
///
/// let secp = Secp256k1::new();
/// let secret_key = SecretKey::new(&mut rand::thread_rng());
/// # }
/// ``` 

[apoelstra]

@tcharding should it fail because rand/std is not enabled? Interesting..

[tcharding]

Yes, because we use thread_rng which needs rand/std. If one puts this same code in a crate and only enable rand it doesn't build.

[apoelstra]

ACK 2732891

Curious that my previous ACK, on this exact commit, no longer counts..