Rust 2018

[c410-f3r]

Converts code-base to Rust 2018 and bumps minimum version to 1.31.

Brought to you by rustfix

[cuviper]

error[E0658]: imports can only refer to extern crate names passed with `--extern` on stable channel (see issue #53130)
  --> rayon-core/src/lib.rs:60:9
   |
45 | mod join;
   | --------- not an extern crate passed with `--extern`
...
60 | pub use join::{join, join_context};
   |         ^^^^
   |
note: this import refers to the module defined here
  --> rayon-core/src/lib.rs:45:1
   |
45 | mod join;
   | ^^^^^^^^^

Looks like 1.32 uniform paths -- you should probably use rustfix/cargo fix from 1.31.

We'll need to increase the minor versions of the crates for our minimum rust policy.
This will also unblock #707.

[c410-f3r]

@cuviper Paths fixed

It is not possible to cargo test or cargo build --all with 1.31 partially because docopt requires 1.32.

[cuviper]

LGTM.

However, #711 showed that windows-gnu CI is broken right now. When that's fixed, I'll probably yield to landing this PR first, then I can fix up my own conflicts.

[cuviper]

I know rustfix does this, but I think this use is not actually needed, as rayon should be in the crate prelude. There are a few cases of this, but I won't comment them all. Not a big deal, just something that could be cleaned up.

[cuviper]

I cut back Windows CI with #714, so let's see how this goes...

bors r+

[bors]

Build succeeded

• continuous-integration/appveyor/branch
• continuous-integration/travis-ci/push

[Tom1380]

Any plans to update to Rust 2021?

[cuviper]

@Tom1380 no specific plans, but we try to support versions of Rust for at least a year:
https://github.com/rayon-rs/rfcs/blob/master/accepted/rfc0003-minimum-rustc.md

I'm not aware of any motivating factor to press for that update. Crates are interoperable across editions.