Un-breaking-change Uuid::new_v4

[CAD97]

I'm submitting a(n) refactor

Description

#447 changed from using rand::thread_rng to using getrandom in Uuid::new_v4. This also changed the return type from Uuid to Result<Uuid, getrandom::Error>. This PR reverts the signature to the simpler new_v4() -> Uuid.

Motivation

This signature is much simpler to use, and avoids a breaking change. getrandom is highly unlikely to fail, and previously we used thread_rng here, which also panics if it fails to initialize from the OS entropy source. If getrandom fails, it is highly unlikely that any program creating v4 UUIDs has any reasonable recovery other than to abort, as the system is in a broken state.

If users absolutely need to recover in this situation, they can call getrandom first themselves to make sure that their system is working, or generate the bytes themselves and create the UUID from those bytes.

Additionally, actually wrapping getrandom::Error in uuid::Error comes with its own fun set of problems, described in #502.

Tests

N/A

Related Issue(s)

#475: this undoes the breaking change to Uuid::new_v4, thus making the requested publish a patch update

Closes #502: alternate approach to the same TODO

[KodrAus]

Thanks @CAD97! It looks like we haven't published a release with the dependency on getrandom. I think treating it as infallible like you're doing here is the best approach.

I'm not sure what state our main branch is at the moment so I've also created a 0.8.x branch off 0.8.1 to backport this to.

[KodrAus]

bors r+

[bors]

Build succeeded:

• continuous-integration/travis-ci/push