argon2: example in documentation doesn't compile with default feature flags

[nikhilraojl]

The example mentioned in documentation (https://docs.rs/argon2/0.5.1/argon2/index.html#password-hashing) doesn't compile with default feature flags.

[dependencies]
argon2 = { version = "0.5.1"}

> cargo clean && cargo build
   Compiling version_check v0.9.4
   Compiling typenum v1.16.0
   Compiling subtle v2.5.0
   Compiling rand_core v0.6.4
   Compiling base64ct v1.6.0
   Compiling cpufeatures v0.2.9
   Compiling password-hash v0.5.0
   Compiling generic-array v0.14.7
   Compiling crypto-common v0.1.6
   Compiling block-buffer v0.10.4
   Compiling digest v0.10.7
   Compiling blake2 v0.10.6
   Compiling argon2 v0.5.1
   Compiling tmp v0.1.0 (...\tmp\rust_tmp)
error[E0432]: unresolved import `argon2::password_hash::rand_core::OsRng`
 --> src\main.rs:3:9
  |
3 |         rand_core::OsRng,
  |         ^^^^^^^^^^^^^^^^ no `OsRng` in the root

For more information about this error, try `rustc --explain E0432`.
error: could not compile `tmp` (bin "tmp") due to previous error

It compiles if std flag is set.

[dependencies]
argon2 = { version = "0.5.1", features = ["std"] }

This wasn't very intuitive. Can the example be updated mentioning that the std feature flag needs to be set?

P.S I am a rust beginner and I may have missed an obvious thing 🙇

[tarcieri]

You're right it doesn't mention the specific feature needed here, although it's actually getrandom and not std (though std will activate it transitively)

[nikhilraojl]

Got it. Can we update the example then? Just a simple line saying this requires the feature flag std

[tarcieri]

Yes, however as I noted the correct feature to enable is getrandom

[nikhilraojl]

As there is no getrandom feature flag on argon2, I have added rand_core and it worked

> cargo add rand_core -F getrandom
    Updating crates.io index
      Adding rand_core v0.6.4 to dependencies.
             Features:
             + getrandom
             - alloc
             - serde
             - serde1
             - std

Is this correct?

[tarcieri]

Oh sorry, you're right, there is currently no getrandom feature and only std will activate it.

To add one, it just needs to activate the getrandom feature of password-hash.