Update rand_core::Error in line with getrandom::Error

[dhardy]

This mirrors the changes in rust-random/getrandom#54 . All changes to rand_core are additive (not breaking).

rand_jitter gets updated to put its error codes within the appropriate range, and also a minor "fix": use of repr(u32) on the enum (which I don't believe is a breaking change, since either way for e: TimerError, e as u32 and e as isize are supported, while u32::from(e) is not).

Open question: should we copy rand_jitter error descriptions into rand_core when cfg(all(feature="getrandom", not(feature="std")))? I'm leaning against doing this, since it increases crate size while benefiting very few people.

Also see #837.

[vks]

So changing the error codes is not considered a breaking change for rand_jitter?

I'm fine with not copying the error descriptions, since I consider rand_jitter to be kind of deprecated.

[newpavlov]

You should use cfg(not(any(feature="getrandom", feature="std"))). Same for Display impl. Maybe use cfg_if to be less error-prone?

[dhardy]

std implies getrandom

[newpavlov]

Maybe write something like this instead?

ifletSome(code) = error.raw_os_error(){
std::io::Error::from_raw_os_error(code)}else{
std::io::Error::new(std::io::ErrorKind::Other, error)}

[newpavlov]

Maybe write it like const ERROR_BASE: u32 = Error::INTERNAL_START + <some const>?

[dhardy]

Is this actually clearer? To me it's not.

[dhardy]

@newpavlov I added your suggestion; sorry about the delay. I think the other points you mentioned can be left?

[newpavlov]

@dhardy Yes, they were just suggestions, so you can merge this PR as-is.

[dhardy]

Failures: cache timeout and Redox failure. Merging.